A toolkit for SQLite databases, with a focus on application development

Latest release: September 8, 2022 • version 5.26.1 • CHANGELOG • Migrating From GRDB 4 to GRDB 5

Requirements: iOS 11.0+ / macOS 10.10+ / tvOS 9.0+ / watchOS 2.0+ • SQLite 3.8.5+ • Swift 5.3+ / Xcode 12+

Contact:

• Release announcements and usage tips: follow @groue on Twitter.
• Report bugs in a Github issue. Make sure you check the existing issues first.
• A question? Looking for advice? Do you wonder how to contribute? Fancy a chat? Go to the GRDB forums, or open a Github issue.

What is this?

GRDB provides raw access to SQL and advanced SQLite features, because one sometimes enjoys a sharp tool. It has robust concurrency primitives, so that multi-threaded applications can efficiently use their databases. It grants your application models with persistence and fetching methods, so that you don’t have to deal with SQL and raw database rows when you don’t want to.

Compared to SQLite.swift or FMDB, GRDB can spare you a lot of glue code. Compared to Core Data or Realm, it can simplify your multi-threaded applications.

It comes with up-to-date documentation, general guides, and it is fast.

See Why Adopt GRDB? if you are looking for your favorite database library.

Features • Usage • Installation • Documentation • FAQ

Features

Programming tools for both database beginners and SQLite experts:

• Access to raw SQL and SQLite
• Records: Fetching and persistence methods for your custom structs and class hierarchies.
• Query Interface: A swift way to avoid the SQL language.
• Associations: Relations and joins between record types.
• WAL Mode Support: Extra performance for multi-threaded applications.
• Migrations: Transform your database as your application evolves.
• Database Observation: Observe database changes and transactions.
• Full-Text Search
• Encryption
• Support for Custom SQLite Builds

In-depth integration with our programming environment:

• Swift Concurrency: try await your database (Xcode 13.3.1+).
• SwiftUI: Access and observe the database from your SwiftUI views.
• Combine: Access and observe the database with Combine publishers.
• RxSwift: Access and observe the database with RxSwift observables.

Usage

Documentation

GRDB runs on top of SQLite: you should get familiar with the SQLite FAQ. For general and detailed information, jump to the SQLite Documentation.

Demo Applications & Frequently Asked Questions

• Demo Applications: Three flavors: vanilla UIKit, Combine + SwiftUI, and Async/Await + SwiftUI.
• FAQ: Opening Connections, Associations, etc.

Reference

• GRDB Reference (generated by Jazzy)

Getting Started

• Installation
• Database Connections: Connect to SQLite databases

SQLite and SQL

• SQLite API: The low-level SQLite API • executing updates • fetch queries • SQL Interpolation

Records and the Query Interface

• Records: Fetching and persistence methods for your custom structs and class hierarchies
• Query Interface: A swift way to generate SQL • table creation • requests • associations between record types

Application Tools

• Migrations: Transform your database as your application evolves.
• Full-Text Search: Perform efficient and customizable full-text searches.
• Joined Queries Support: Consume complex joined queries.
• Database Observation: Observe database changes and transactions.
• Encryption: Encrypt your database with SQLCipher.
• Backup: Dump the content of a database to another.
• Interrupt a Database: Abort any pending database operation.
• Sharing a Database: Recommendations for App Group Containers and sandboxed macOS apps.

Good to Know

• Avoiding SQL Injection
• Error Handling
• Unicode
• Memory Management
• Data Protection
• Concurrency

General Guides & Good Practices

• :bulb: Good Practices for Designing Record Types
• :bulb: Migrating From GRDB 4 to GRDB 5
• :bulb: Issues tagged "best practices”
• :question: Issues tagged “question”
• :blue_book: Why Adopt GRDB?
• :blue_book: How to build an iOS application with SQLite and GRDB.swift
• :blue_book: Four different ways to handle SQLite concurrency
• :blue_book: Unexpected SQLite with Swift

FAQ

Sample Code

Installation

The installation procedures below have GRDB use the version of SQLite that ships with the target operating system.

See Encryption for the installation procedure of GRDB with SQLCipher.

See Custom SQLite builds for the installation procedure of GRDB with a customized build of SQLite.

See Enabling FTS5 Support for the installation procedure of GRDB with support for the FTS5 full-text engine.

CocoaPods

CocoaPods is a dependency manager for Xcode projects. To use GRDB with CocoaPods (version 1.2 or higher), specify in your Podfile:

pod 'GRDB.swift'

GRDB can be installed as a framework, or a static library.

Swift Package Manager

The Swift Package Manager automates the distribution of Swift code. To use GRDB with SPM, add a dependency to https://github.com/groue/GRDB.swift.git

GRDB offers two libraries, GRDB and GRDB-dynamic. Pick only one. When in doubt, prefer GRDB. The GRDB-dynamic library can reveal useful if you are going to link it with multiple targets within your app and only wish to link to a shared, dynamic framework once. See How to link a Swift Package as dynamic for more information.

:point_up: Note: Linux is not currently supported.

:warning: Warning: Due to an Xcode bug, you will get “No such module ‘CSQLite’” errors when you want to embed the GRDB package in other targets than the main application (watch extensions, for example). UI and Unit testing targets are OK, though. See #642 for more information.

Carthage

Carthage is unsupported. For some context about this decision, see #433.

Manually

1. Download a copy of GRDB, or clone its repository and make sure you checkout the latest tagged version.

2. Embed the GRDB.xcodeproj project in your own project.

3. Add the GRDBOSX, GRDBiOS, GRDBtvOS, or GRDBWatchOS target in the Target Dependencies section of the Build Phases tab of your application target (extension target for WatchOS).

4. Add the GRDB.framework from the targeted platform to the Embedded Binaries section of the General tab of your application target (extension target for WatchOS).

:bulb: Tip: see the Demo Applications for examples of such integration.

Database Connections

GRDB provides two classes for accessing SQLite databases: DatabaseQueue and DatabasePool:

import GRDB

// Pick one:
let dbQueue = try DatabaseQueue(path: "/path/to/database.sqlite")
let dbPool = try DatabasePool(path: "/path/to/database.sqlite")

The differences are:

• Database pools allow concurrent database accesses (this can improve the performance of multithreaded applications).
• Database pools open your SQLite database in the WAL mode (unless read-only).
• Database queues support in-memory databases.

If you are not sure, choose DatabaseQueue. You will always be able to switch to DatabasePool later.

• Database Queues
• Database Pools

Database Queues

Open a database queue with the path to a database file:

import GRDB

let dbQueue = try DatabaseQueue(path: "/path/to/database.sqlite")
let inMemoryDBQueue = DatabaseQueue()

SQLite creates the database file if it does not already exist. The connection is closed when the database queue gets deinitialized.

A database queue can be used from any thread. The write and read methods are synchronous, and block the current thread until your database statements are executed in a protected dispatch queue:

// Modify the database:
try dbQueue.write { db in
    try db.create(table: "place") { ... }
    try Place(...).insert(db)
}

// Read values:
try dbQueue.read { db in
    let places = try Place.fetchAll(db)
    let placeCount = try Place.fetchCount(db)
}

Database access methods can return values:

let placeCount = try dbQueue.read { db in
    try Place.fetchCount(db)
}

let newPlaceCount = try dbQueue.write { db -> Int in
    try Place(...).insert(db)
    return try Place.fetchCount(db)
}

See the Concurrency guide for asynchronous database accesses.

A database queue serializes accesses to the database, which means that there is never more than one thread that uses the database.

• When you don’t need to modify the database, prefer the read method. It prevents any modification to the database.

• The write method wraps your database statements in a transaction that commits if and only if no error occurs. On the first unhandled error, all changes are reverted, the whole transaction is rollbacked, and the error is rethrown.

  When precise transaction handling is required, see Transactions and Savepoints.

A database queue needs your application to follow rules in order to deliver its safety guarantees. Please refer to the Concurrency guide.

See Database Configuration for DatabaseQueue options.

:bulb: Tip: see the Demo Applications for sample code.

Database Pools

A database pool allows concurrent database accesses.

import GRDB
let dbPool = try DatabasePool(path: "/path/to/database.sqlite")

SQLite creates the database file if it does not already exist. The connection is closed when the database pool gets deinitialized.

:point_up: Note: unless read-only, a database pool opens your database in the SQLite “WAL mode”. The WAL mode does not fit all situations. Please have a look at https://www.sqlite.org/wal.html.

A database pool can be used from any thread. The write and read methods are synchronous, and block the current thread until your database statements are executed in a protected dispatch queue:

// Modify the database:
try dbPool.write { db in
    try db.create(table: "place") { ... }
    try Place(...).insert(db)
}

// Read values:
try dbPool.read { db in
    let places = try Place.fetchAll(db)
    let placeCount = try Place.fetchCount(db)
}

Database access methods can return values:

let placeCount = try dbPool.read { db in
    try Place.fetchCount(db)
}

let newPlaceCount = try dbPool.write { db -> Int in
    try Place(...).insert(db)
    return try Place.fetchCount(db)
}

See the Concurrency guide for asynchronous database accesses.

Database pools allow several threads to access the database at the same time:

• When you don’t need to modify the database, prefer the read method, because several threads can perform reads in parallel.

  Reads are generally non-blocking, unless the maximum number of concurrent reads has been reached. In this case, a read has to wait for another read to complete. That maximum number can be configured.

• Reads are guaranteed an immutable view of the last committed state of the database, regardless of concurrent writes. This kind of isolation is called snapshot isolation.

• Unlike reads, writes are serialized. There is never more than a single thread that is writing into the database.

• The write method wraps your database statements in a transaction that commits if and only if no error occurs. On the first unhandled error, all changes are reverted, the whole transaction is rollbacked, and the error is rethrown.

  When precise transaction handling is required, see Transactions and Savepoints.

• Database pools can take snapshots of the database.

A database pool needs your application to follow rules in order to deliver its safety guarantees. See the Concurrency guide for more details about database pools, how they differ from database queues, and advanced use cases.

See Database Configuration for DatabasePool options.

:bulb: Tip: see the Demo Applications for sample code.

Database Configuration

var config = Configuration()
config.readonly = true
config.foreignKeysEnabled = true // Default is already true
config.label = "MyDatabase"      // Useful when your app opens multiple databases
config.maximumReaderCount = 10   // (DatabasePool only) The default is 5

let dbQueue = try DatabaseQueue( // or DatabasePool
    path: "/path/to/database.sqlite",
    configuration: config)

In debug builds, you can increase the verbosity of error descriptions and trace events if you opt in for public statement arguments:

#if DEBUG
// Protect sensitive information by enabling verbose debugging in DEBUG builds only
config.publicStatementArguments = true
#endif

let dbQueue = try DatabaseQueue(path: ..., configuration: config)

do {
    try dbQueue.write { db in
        user.name = ...
        user.location = ...
        user.address = ...
        user.phoneNumber = ...
        try user.save(db)
    }
} catch {
    // Prints sensitive information in debug builds only
    print(error)
}

:warning: Warning: It is your responsibility to prevent sensitive information from leaking in unexpected locations, so you should not set the publicStatementArguments flag in release builds (think about GDPR and other privacy-related rules).

:warning: Warning: The SQLite version that ships with old operating systems (prior to OSX 10.12, tvOS 10.0, and watchOS 3.0) outputs statement arguments in the trace events, regardless of the publicStatementArguments flag.

See Configuration for more details and configuration options.

SQLite API

In this section of the documentation, we will talk SQL. Jump to the query interface if SQL is not your cup of tea.

• Executing Updates
• Fetch Queries
  • Fetching Methods
  • Row Queries
  • Value Queries
• Values
  • Data
  • Date and DateComponents
  • NSNumber, NSDecimalNumber, and Decimal
  • Swift enums
  • Custom Value Types
• Transactions and Savepoints
• SQL Interpolation

Advanced topics:

• Prepared Statements
• Custom SQL Functions and Aggregates
• Database Schema Introspection
• Row Adapters
• Raw SQLite Pointers

Executing Updates

Once granted with a database connection, the execute method executes the SQL statements that do not return any database row, such as CREATE TABLE, INSERT, DELETE, ALTER, etc.

For example:

try dbQueue.write { db in
    try db.execute(sql: """
        CREATE TABLE player (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            name TEXT NOT NULL,
            score INT)
        """)

    try db.execute(
        sql: "INSERT INTO player (name, score) VALUES (?, ?)",
        arguments: ["Barbara", 1000])

    try db.execute(
        sql: "UPDATE player SET score = :score WHERE id = :id",
        arguments: ["score": 1000, "id": 1])
    }
}

The ? and colon-prefixed keys like :score in the SQL query are the statements arguments. You pass arguments with arrays or dictionaries, as in the example above. See Values for more information on supported arguments types (Bool, Int, String, Date, Swift enums, etc.), and StatementArguments for a detailed documentation of SQLite arguments.

You can also embed query arguments right into your SQL queries, with the literal argument label, as in the example below. See SQL Interpolation for more details.

try dbQueue.write { db in
    try db.execute(literal: """
        INSERT INTO player (name, score) VALUES (\("O'Brien"), \(550))
        """)
}

Never ever embed values directly in your raw SQL strings. See Avoiding SQL Injection for more information:

// WRONG: don't embed values in raw SQL strings
let id = 123
let name = textField.text
try db.execute(
    sql: "UPDATE player SET name = '\(name)' WHERE id = \(id)")

// CORRECT: use arguments dictionary
try db.execute(
    sql: "UPDATE player SET name = :name WHERE id = :id",
    arguments: ["name": name, "id": id])

// CORRECT: use arguments array
try db.execute(
    sql: "UPDATE player SET name = ? WHERE id = ?",
    arguments: [name, id])

// CORRECT: use SQL Interpolation
try db.execute(
    literal: "UPDATE player SET name = \(name) WHERE id = \(id)")

Join multiple statements with a semicolon:

try db.execute(sql: """
    INSERT INTO player (name, score) VALUES (?, ?);
    INSERT INTO player (name, score) VALUES (?, ?);
    """, arguments: ["Arthur", 750, "Barbara", 1000])

try db.execute(literal: """
    INSERT INTO player (name, score) VALUES (\("Arthur"), \(750));
    INSERT INTO player (name, score) VALUES (\("Barbara"), \(1000));
    """)

When you want to make sure that a single statement is executed, use Prepared Statements.

After an INSERT statement, you can get the row ID of the inserted row:

try db.execute(
    sql: "INSERT INTO player (name, score) VALUES (?, ?)",
    arguments: ["Arthur", 1000])
let playerId = db.lastInsertedRowID

Don’t miss Records, that provide classic persistence methods:

var player = Player(name: "Arthur", score: 1000)
try player.insert(db)
let playerId = player.id

Fetch Queries

Database connections let you fetch database rows, plain values, and custom models aka “records”.

Rows are the raw results of SQL queries:

try dbQueue.read { db in
    if let row = try Row.fetchOne(db, sql: "SELECT * FROM wine WHERE id = ?", arguments: [1]) {
        let name: String = row["name"]
        let color: Color = row["color"]
        print(name, color)
    }
}

Values are the Bool, Int, String, Date, Swift enums, etc. stored in row columns:

try dbQueue.read { db in
    let urls = try URL.fetchCursor(db, sql: "SELECT url FROM wine")
    while let url = try urls.next() {
        print(url)
    }
}

Records are your application objects that can initialize themselves from rows:

let wines = try dbQueue.read { db in
    try Wine.fetchAll(db, sql: "SELECT * FROM wine")
}

• Fetching Methods and Cursors
• Row Queries
• Value Queries
• Records

Fetching Methods

Throughout GRDB, you can always fetch cursors, arrays, sets, or single values of any fetchable type (database row, simple value, or custom record):

try Row.fetchCursor(...) // A Cursor of Row
try Row.fetchAll(...)    // [Row]
try Row.fetchSet(...)    // Set<Row>
try Row.fetchOne(...)    // Row?

• fetchCursor returns a cursor over fetched values:

  let rows = try Row.fetchCursor(db, sql: "SELECT ...") // A Cursor of Row
  

• fetchAll returns an array:

  let players = try Player.fetchAll(db, sql: "SELECT ...") // [Player]
  

• fetchSet returns a set:

  let names = try String.fetchSet(db, sql: "SELECT ...") // Set<String>
  

• fetchOne returns a single optional value, and consumes a single database row (if any).

  let count = try Int.fetchOne(db, sql: "SELECT COUNT(*) ...") // Int?
  

All those fetching methods require an SQL string that contains a single SQL statement. When you want to fetch from multiple statements joined with a semicolon, iterate the multiple prepared statements found in the SQL string:

let statements = try db.allStatements(sql: """
    SELECT ...; 
    SELECT ...; 
    SELECT ...;
    """)
while let statement = try statements.next() {
    let players = try Player.fetchAll(statement)
}

You can join the results of all statements yielded by the allStatements method, like the SQLite sqlite3_exec function:

// A single cursor of all rows from all statements
let rows = try db
    .allStatements(sql: "...")
    .flatMap { statement in try Row.fetchCursor(statement) }

See prepared statements for more information about allStatements().

Cursors

Whenever you consume several rows from the database, you can fetch an Array, a Set, or a Cursor.

The fetchAll() and fetchSet() methods return regular Swift array and sets, that you iterate like all other arrays and sets:

try dbQueue.read { db in
    // [Player]
    let players = try Player.fetchAll(db, sql: "SELECT ...")
    for player in players {
        // use player
    }
}

Unlike arrays and sets, cursors returned by fetchCursor() load their results step after step:

try dbQueue.read { db in
    // Cursor of Player
    let players = try Player.fetchCursor(db, sql: "SELECT ...")
    while let player = try players.next() {
        // use player
    }
}

• Cursors can not be used on any thread: you must consume a cursor on the dispatch queue it was created in. Particularly, don’t extract a cursor out of a database access method:

  // Wrong
  let cursor = try dbQueue.read { db in
      try Player.fetchCursor(db, ...)
  }
  while let player = try cursor.next() { ... }
  

  Conversely, arrays and sets may be consumed on any thread:

  // OK
  let array = try dbQueue.read { db in
      try Player.fetchAll(db, ...)
  }
  for player in array { ... }
  

• Cursors can be iterated only one time. Arrays and sets can be iterated many times.

• Cursors iterate database results in a lazy fashion, and don’t consume much memory. Arrays and sets contain copies of database values, and may take a lot of memory when there are many fetched results.

• Cursors are granted with direct access to SQLite, unlike arrays and sets that have to take the time to copy database values. If you look after extra performance, you may prefer cursors.

• Cursors can feed Swift collections.

  You will most of the time use fetchAll or fetchSet when you want an array or a set. For more specific needs, you may prefer one of the initializers below. All of them accept an extra optional minimumCapacity argument which helps optimizing your app when you have an idea of the number of elements in a cursor (the built-in fetchAll and fetchSet do not perform such an optimization).

  Arrays and all types conforming to RangeReplaceableCollection:

  // [String]
  let cursor = try String.fetchCursor(db, ...)
  let array = try Array(cursor)
  

  Sets:

  // Set<Int>
  let cursor = try Int.fetchCursor(db, ...)
  let set = try Set(cursor)
  

  Dictionaries:

  // [Int64: [Player]]
  let cursor = try Player.fetchCursor(db)
  let dictionary = try Dictionary(grouping: cursor, by: { $0.teamID })
  
  // [Int64: Player]
  let cursor = try Player.fetchCursor(db).map { ($0.id, $0) }
  let dictionary = try Dictionary(uniqueKeysWithValues: cursor)
  

• Cursors adopt the Cursor protocol, which looks a lot like standard lazy sequences of Swift. As such, cursors come with many convenience methods: compactMap, contains, dropFirst, dropLast, drop(while:), enumerated, filter, first, flatMap, forEach, joined, joined(separator:), max, max(by:), min, min(by:), map, prefix, prefix(while:), reduce, reduce(into:), suffix:

  // Prints all Github links
  try URL
      .fetchCursor(db, sql: "SELECT url FROM link")
      .filter { url in url.host == "github.com" }
      .forEach { url in print(url) }
  
  // An efficient cursor of coordinates:
  let locations = try Row.
      .fetchCursor(db, sql: "SELECT latitude, longitude FROM place")
      .map { row in
          CLLocationCoordinate2D(latitude: row[0], longitude: row[1])
      }
  

• Cursors are not Swift sequences. That’s because Swift sequences can’t handle iteration errors, when reading SQLite results may fail at any time.

• Cursors require a little care:

  • Don’t modify the results during a cursor iteration:

    // Undefined behavior
    while let player = try players.next() {
        try db.execute(sql: "DELETE ...")
    }
    

  • Don’t turn a cursor of Row into an array or a set. You would not get the distinct rows you expect. To get a array of rows, use Row.fetchAll(...). To get a set of rows, use Row.fetchSet(...). Generally speaking, make sure you copy a row whenever you extract it from a cursor for later use: row.copy().

If you don’t see, or don’t care about the difference, use arrays. If you care about memory and performance, use cursors when appropriate.

Row Queries

• Fetching Rows
• Column Values
• DatabaseValue
• Rows as Dictionaries

Fetching Rows

Fetch cursors of rows, arrays, sets, or single rows (see fetching methods):

try dbQueue.read { db in
    try Row.fetchCursor(db, sql: "SELECT ...", arguments: ...) // A Cursor of Row
    try Row.fetchAll(db, sql: "SELECT ...", arguments: ...)    // [Row]
    try Row.fetchSet(db, sql: "SELECT ...", arguments: ...)    // Set<Row>
    try Row.fetchOne(db, sql: "SELECT ...", arguments: ...)    // Row?

    let rows = try Row.fetchCursor(db, sql: "SELECT * FROM wine")
    while let row = try rows.next() {
        let name: String = row["name"]
        let color: Color = row["color"]
        print(name, color)
    }
}

let rows = try dbQueue.read { db in
    try Row.fetchAll(db, sql: "SELECT * FROM player")
}

Arguments are optional arrays or dictionaries that fill the positional ? and colon-prefixed keys like :name in the query:

let rows = try Row.fetchAll(db,
    sql: "SELECT * FROM player WHERE name = ?",
    arguments: ["Arthur"])

let rows = try Row.fetchAll(db,
    sql: "SELECT * FROM player WHERE name = :name",
    arguments: ["name": "Arthur"])

See Values for more information on supported arguments types (Bool, Int, String, Date, Swift enums, etc.), and StatementArguments for a detailed documentation of SQLite arguments.

Unlike row arrays that contain copies of the database rows, row cursors are close to the SQLite metal, and require a little care:

:point_up: Don’t turn a cursor of Row into an array or a set. You would not get the distinct rows you expect. To get a array of rows, use Row.fetchAll(...). To get a set of rows, use Row.fetchSet(...). Generally speaking, make sure you copy a row whenever you extract it from a cursor for later use: row.copy().

Column Values

Read column values by index or column name:

let name: String = row[0]      // 0 is the leftmost column
let name: String = row["name"] // Leftmost matching column - lookup is case-insensitive
let name: String = row[Column("name")] // Using query interface's Column

Make sure to ask for an optional when the value may be NULL:

let name: String? = row["name"]

The row[] subscript returns the type you ask for. See Values for more information on supported value types:

let bookCount: Int     = row["bookCount"]
let bookCount64: Int64 = row["bookCount"]
let hasBooks: Bool     = row["bookCount"] // false when 0

let string: String     = row["date"]      // "2015-09-11 18:14:15.123"
let date: Date         = row["date"]      // Date
self.date = row["date"] // Depends on the type of the property.

You can also use the as type casting operator:

row[...] as Int
row[...] as Int?

:warning: Warning: avoid the as! and as? operators:

if let int = row[...] as? Int { ... } // BAD - doesn't work
if let int = row[...] as Int? { ... } // GOOD

Generally speaking, you can extract the type you need, provided it can be converted from the underlying SQLite value:

• Successful conversions include:

  • All numeric SQLite values to all numeric Swift types, and Bool (zero is the only false boolean).
  • Text SQLite values to Swift String.
  • Blob SQLite values to Foundation Data.

  See Values for more information on supported types (Bool, Int, String, Date, Swift enums, etc.)

• NULL returns nil.

  let row = try Row.fetchOne(db, sql: "SELECT NULL")!
  row[0] as Int? // nil
  row[0] as Int  // fatal error: could not convert NULL to Int.
  

  There is one exception, though: the DatabaseValue type:

  row[0] as DatabaseValue // DatabaseValue.null
  

• Missing columns return nil.

  let row = try Row.fetchOne(db, sql: "SELECT 'foo' AS foo")!
  row["missing"] as String? // nil
  row["missing"] as String  // fatal error: no such column: missing
  

  You can explicitly check for a column presence with the hasColumn method.

• Invalid conversions throw a fatal error.

  let row = try Row.fetchOne(db, sql: "SELECT 'Mom’s birthday'")!
  row[0] as String // "Mom’s birthday"
  row[0] as Date?  // fatal error: could not convert "Mom’s birthday" to Date.
  row[0] as Date   // fatal error: could not convert "Mom’s birthday" to Date.
  
  let row = try Row.fetchOne(db, sql: "SELECT 256")!
  row[0] as Int    // 256
  row[0] as UInt8? // fatal error: could not convert 256 to UInt8.
  row[0] as UInt8  // fatal error: could not convert 256 to UInt8.
  

  Those conversion fatal errors can be avoided with the DatabaseValue type:

  let row = try Row.fetchOne(db, sql: "SELECT 'Mom’s birthday'")!
  let dbValue: DatabaseValue = row[0]
  if dbValue.isNull {
      // Handle NULL
  } else if let date = Date.fromDatabaseValue(dbValue) {
      // Handle valid date
  } else {
      // Handle invalid date
  }
  

  This extra verbosity is the consequence of having to deal with an untrusted database: you may consider fixing the content of your database instead. See Fatal Errors for more information.

• SQLite has a weak type system, and provides convenience conversions that can turn String to Int, Double to Blob, etc.

  GRDB will sometimes let those conversions go through:

  let rows = try Row.fetchCursor(db, sql: "SELECT '20 small cigars'")
  while let row = try rows.next() {
      row[0] as Int   // 20
  }
  

  Don’t freak out: those conversions did not prevent SQLite from becoming the immensely successful database engine you want to use. And GRDB adds safety checks described just above. You can also prevent those convenience conversions altogether by using the DatabaseValue type.

DatabaseValue

DatabaseValue is an intermediate type between SQLite and your values, which gives information about the raw value stored in the database.

You get DatabaseValue just like other value types:

let dbValue: DatabaseValue = row[0]
let dbValue: DatabaseValue? = row["name"] // nil if and only if column does not exist

// Check for NULL:
dbValue.isNull // Bool

// The stored value:
dbValue.storage.value // Int64, Double, String, Data, or nil

// All the five storage classes supported by SQLite:
switch dbValue.storage {
case .null:                 print("NULL")
case .int64(let int64):     print("Int64: \(int64)")
case .double(let double):   print("Double: \(double)")
case .string(let string):   print("String: \(string)")
case .blob(let data):       print("Data: \(data)")
}

You can extract regular values (Bool, Int, String, Date, Swift enums, etc.) from DatabaseValue with the DatabaseValueConvertible.fromDatabaseValue() method:

let dbValue: DatabaseValue = row["bookCount"]
let bookCount   = Int.fromDatabaseValue(dbValue)   // Int?
let bookCount64 = Int64.fromDatabaseValue(dbValue) // Int64?
let hasBooks    = Bool.fromDatabaseValue(dbValue)  // Bool?, false when 0

let dbValue: DatabaseValue = row["date"]
let string = String.fromDatabaseValue(dbValue)     // "2015-09-11 18:14:15.123"
let date   = Date.fromDatabaseValue(dbValue)       // Date?

fromDatabaseValue returns nil for invalid conversions:

let row = try Row.fetchOne(db, sql: "SELECT 'Mom’s birthday'")!
let dbValue: DatabaseValue = row[0]
let string = String.fromDatabaseValue(dbValue) // "Mom’s birthday"
let int    = Int.fromDatabaseValue(dbValue)    // nil
let date   = Date.fromDatabaseValue(dbValue)   // nil

Rows as Dictionaries

Row adopts the standard RandomAccessCollection protocol, and can be seen as a dictionary of DatabaseValue:

// All the (columnName, dbValue) tuples, from left to right:
for (columnName, dbValue) in row {
    ...
}

You can build rows from dictionaries (standard Swift dictionaries and NSDictionary). See Values for more information on supported types:

let row: Row = ["name": "foo", "date": nil]
let row = Row(["name": "foo", "date": nil])
let row = Row(/* [AnyHashable: Any] */) // nil if invalid dictionary

Yet rows are not real dictionaries: they may contain duplicate columns:

let row = try Row.fetchOne(db, sql: "SELECT 1 AS foo, 2 AS foo")!
row.columnNames    // ["foo", "foo"]
row.databaseValues // [1, 2]
row["foo"]         // 1 (leftmost matching column)
for (columnName, dbValue) in row { ... } // ("foo", 1), ("foo", 2)

When you build a dictionary from a row, you have to disambiguate identical columns, and choose how to present database values. For example:

• A [String: DatabaseValue] dictionary that keeps leftmost value in case of duplicated column name:

  let dict = Dictionary(row, uniquingKeysWith: { (left, _) in left })
  

• A [String: AnyObject] dictionary which keeps rightmost value in case of duplicated column name. This dictionary is identical to FMResultSet’s resultDictionary from FMDB. It contains NSNull values for null columns, and can be shared with Objective-C:

  let dict = Dictionary(
      row.map { (column, dbValue) in
          (column, dbValue.storage.value as AnyObject)
      },
      uniquingKeysWith: { (_, right) in right })
  

• A [String: Any] dictionary that can feed, for example, JSONSerialization:

  let dict = Dictionary(
      row.map { (column, dbValue) in
          (column, dbValue.storage.value)
      },
      uniquingKeysWith: { (left, _) in left })
  

See the documentation of Dictionary.init(_:uniquingKeysWith:) for more information.

Value Queries

Instead of rows, you can directly fetch values. Like rows, fetch them as cursors, arrays, sets, or single values (see fetching methods). Values are extracted from the leftmost column of the SQL queries:

try dbQueue.read { db in
    try Int.fetchCursor(db, sql: "SELECT ...", arguments: ...) // A Cursor of Int
    try Int.fetchAll(db, sql: "SELECT ...", arguments: ...)    // [Int]
    try Int.fetchSet(db, sql: "SELECT ...", arguments: ...)    // Set<Int>
    try Int.fetchOne(db, sql: "SELECT ...", arguments: ...)    // Int?

    // When database may contain NULL:
    try Optional<Int>.fetchCursor(db, sql: "SELECT ...", arguments: ...) // A Cursor of Int?
    try Optional<Int>.fetchAll(db, sql: "SELECT ...", arguments: ...)    // [Int?]
    try Optional<Int>.fetchSet(db, sql: "SELECT ...", arguments: ...)    // Set<Int?>
}

let playerCount = try dbQueue.read { db in
    try Int.fetchOne(db, sql: "SELECT COUNT(*) FROM player")!
}

fetchOne returns an optional value which is nil in two cases: either the SELECT statement yielded no row, or one row with a NULL value.

There are many supported value types (Bool, Int, String, Date, Swift enums, etc.). See Values for more information:

let count = try Int.fetchOne(db, sql: "SELECT COUNT(*) FROM player")! // Int
let urls = try URL.fetchAll(db, sql: "SELECT url FROM link")          // [URL]

Values

GRDB ships with built-in support for the following value types:

• Swift Standard Library: Bool, Double, Float, all signed and unsigned integer types, String, Swift enums.

• Foundation: Data, Date, DateComponents, Decimal, NSNull, NSNumber, NSString, URL, UUID.

• CoreGraphics: CGFloat.

• DatabaseValue, the type which gives information about the raw value stored in the database.

• Full-Text Patterns: FTS3Pattern and FTS5Pattern.

• Generally speaking, all types that adopt the DatabaseValueConvertible protocol.

Values can be used as statement arguments:

let url: URL = ...
let verified: Bool = ...
try db.execute(
    sql: "INSERT INTO link (url, verified) VALUES (?, ?)",
    arguments: [url, verified])

Values can be extracted from rows:

let rows = try Row.fetchCursor(db, sql: "SELECT * FROM link")
while let row = try rows.next() {
    let url: URL = row["url"]
    let verified: Bool = row["verified"]
}

Values can be directly fetched:

let urls = try URL.fetchAll(db, sql: "SELECT url FROM link")  // [URL]

Use values in Records:

struct Link: FetchableRecord {
    var url: URL
    var isVerified: Bool

    init(row: Row) {
        url = row["url"]
        isVerified = row["verified"]
    }
}

Use values in the query interface:

let url: URL = ...
let link = try Link.filter(Column("url") == url).fetchOne(db)

Data (and Memory Savings)

Data suits the BLOB SQLite columns. It can be stored and fetched from the database just like other values:

let rows = try Row.fetchCursor(db, sql: "SELECT data, ...")
while let row = try rows.next() {
    let data: Data = row["data"]
}

At each step of the request iteration, the row[] subscript creates two copies of the database bytes: one fetched by SQLite, and another, stored in the Swift Data value.

You have the opportunity to save memory by not copying the data fetched by SQLite:

while let row = try rows.next() {
    let data = row.dataNoCopy(named: "data") // Data?
}

The non-copied data does not live longer than the iteration step: make sure that you do not use it past this point.

Date and DateComponents

Date and DateComponents can be stored and fetched from the database.

Here is how GRDB supports the various date formats supported by SQLite:

¹ Missing components are assumed to be zero. Dates are stored and read in the UTC time zone, unless the format is followed by a timezone indicator ⁽²⁾.

² This format may be optionally followed by a timezone indicator of the form [+-]HH:MM or just Z.

³ GRDB 2+ interprets numerical values as timestamps that fuel Date(timeIntervalSince1970:). Previous GRDB versions used to interpret numbers as julian days. Julian days are still supported, with the Date(julianDay:) initializer.

:warning: Warning: the range of valid years in the SQLite date formats is 0000-9999. You will need to pick another date format when your application needs to process years outside of this range. See the following chapters.

Date

Date can be stored and fetched from the database just like other values:

try db.execute(
    sql: "INSERT INTO player (creationDate, ...) VALUES (?, ...)",
    arguments: [Date(), ...])

let row = try Row.fetchOne(db, ...)!
let creationDate: Date = row["creationDate"]

Dates are stored using the format “YYYY-MM-DD HH:MM:SS.SSS” in the UTC time zone. It is precise to the millisecond.

:point_up: Note: this format was chosen because it is the only format that is:

• Comparable (ORDER BY date works)
• Comparable with the SQLite keyword CURRENT_TIMESTAMP (WHERE date > CURRENT_TIMESTAMP works)
• Able to feed SQLite date & time functions
• Precise enough

:warning: Warning: the range of valid years in the SQLite date format is 0000-9999. You will experience problems with years outside of this range, such as decoding errors, or invalid date computations with SQLite date & time functions.

Some applications may prefer another date format:

• Some may prefer ISO-8601, with a T separator.
• Some may prefer ISO-8601, with a time zone.
• Some may need to store years beyond the 0000-9999 range.
• Some may need sub-millisecond precision.
• Some may need exact Date roundtrip.
• Etc.

You should think twice before choosing a different date format:

• ISO-8601 is about exchange and communication, when SQLite is about storage and data manipulation. Sharing the same representation in your database and in JSON files only provides a superficial convenience, and should be the least of your priorities. Don’t store dates as ISO-8601 without understanding what you lose. For example, ISO-8601 time zones forbid database-level date comparison.
• Sub-millisecond precision and exact Date roundtrip are not as obvious needs as it seems at first sight. Dates generally don’t precisely roundtrip as soon as they leave your application anyway, because the other systems your app communicates with use their own date representation (the Android version of your app, the server your application is talking to, etc.) On top of that, Date comparison is at least as hard and nasty as floating point comparison.

The customization of date format is explicit. For example:

let date = Date()
let timeInterval = date.timeIntervalSinceReferenceDate
try db.execute(
    sql: "INSERT INTO player (creationDate, ...) VALUES (?, ...)",
    arguments: [timeInterval, ...])

if let row = try Row.fetchOne(db, ...) {
    let timeInterval: TimeInterval = row["creationDate"]
    let creationDate = Date(timeIntervalSinceReferenceDate: timeInterval)
}

See also Codable Records for more date customization options, and DatabaseValueConvertible if you want to define a Date-wrapping type with customized database representation.

DateComponents

DateComponents is indirectly supported, through the DatabaseDateComponents helper type.

DatabaseDateComponents reads date components from all date formats supported by SQLite, and stores them in the format of your choice, from HH:MM to YYYY-MM-DD HH:MM:SS.SSS.

:warning: Warning: the range of valid years is 0000-9999. You will experience problems with years outside of this range, such as decoding errors, or invalid date computations with SQLite date & time functions. See Date for more information.

DatabaseDateComponents can be stored and fetched from the database just like other values:

let components = DateComponents()
components.year = 1973
components.month = 9
components.day = 18

// Store "1973-09-18"
let dbComponents = DatabaseDateComponents(components, format: .YMD)
try db.execute(
    sql: "INSERT INTO player (birthDate, ...) VALUES (?, ...)",
    arguments: [dbComponents, ...])

// Read "1973-09-18"
let row = try Row.fetchOne(db, sql: "SELECT birthDate ...")!
let dbComponents: DatabaseDateComponents = row["birthDate"]
dbComponents.format         // .YMD (the actual format found in the database)
dbComponents.dateComponents // DateComponents

NSNumber, NSDecimalNumber, and Decimal

NSNumber and Decimal can be stored and fetched from the database just like other values.

Here is how GRDB supports the various data types supported by SQLite:

• All three types can decode database integers and doubles:

  let number = try NSNumber.fetchOne(db, sql: "SELECT 10")            // NSNumber
  let number = try NSDecimalNumber.fetchOne(db, sql: "SELECT 1.23")   // NSDecimalNumber
  let number = try Decimal.fetchOne(db, sql: "SELECT -100")           // Decimal
  

• All three types decode database strings as decimal numbers:

  let number = try NSNumber.fetchOne(db, sql: "SELECT '10'")          // NSDecimalNumber (sic)
  let number = try NSDecimalNumber.fetchOne(db, sql: "SELECT '1.23'") // NSDecimalNumber
  let number = try Decimal.fetchOne(db, sql: "SELECT '-100'")         // Decimal
  

• NSNumber and NSDecimalNumber send 64-bit signed integers and doubles in the database:

  // INSERT INTO transfer VALUES (10)
  try db.execute(sql: "INSERT INTO transfer VALUES (?)", arguments: [NSNumber(value: 10)])
  
  // INSERT INTO transfer VALUES (10.0)
  try db.execute(sql: "INSERT INTO transfer VALUES (?)", arguments: [NSNumber(value: 10.0)])
  
  // INSERT INTO transfer VALUES (10)
  try db.execute(sql: "INSERT INTO transfer VALUES (?)", arguments: [NSDecimalNumber(string: "10.0")])
  
  // INSERT INTO transfer VALUES (10.5)
  try db.execute(sql: "INSERT INTO transfer VALUES (?)", arguments: [NSDecimalNumber(string: "10.5")])
  

  :warning: Warning: since SQLite does not support decimal numbers, sending a non-integer NSDecimalNumber can result in a loss of precision during the conversion to double.

  Instead of sending non-integer NSDecimalNumber to the database, you may prefer:

  • Send Decimal instead (those store decimal strings in the database).
  • Send integers instead (for example, store amounts of cents instead of amounts of Euros).

• Decimal sends decimal strings in the database:

  // INSERT INTO transfer VALUES ('10')
  try db.execute(sql: "INSERT INTO transfer VALUES (?)", arguments: [Decimal(10)])
  
  // INSERT INTO transfer VALUES ('10.5')
  try db.execute(sql: "INSERT INTO transfer VALUES (?)", arguments: [Decimal(string: "10.5")!])
  

UUID

UUID can be stored and fetched from the database just like other values.

GRDB stores uuids as 16-bytes data blobs, and decodes them from both 16-bytes data blobs and strings such as “E621E1F8-C36C-495A-93FC-0C247A3E6E5F”.

Swift Enums

Swift enums and generally all types that adopt the RawRepresentable protocol can be stored and fetched from the database just like their raw values:

enum Color : Int {
    case red, white, rose
}

enum Grape : String {
    case chardonnay, merlot, riesling
}

// Declare empty DatabaseValueConvertible adoption
extension Color : DatabaseValueConvertible { }
extension Grape : DatabaseValueConvertible { }

// Store
try db.execute(
    sql: "INSERT INTO wine (grape, color) VALUES (?, ?)",
    arguments: [Grape.merlot, Color.red])

// Read
let rows = try Row.fetchCursor(db, sql: "SELECT * FROM wine")
while let row = try rows.next() {
    let grape: Grape = row["grape"]
    let color: Color = row["color"]
}

When a database value does not match any enum case, you get a fatal error. This fatal error can be avoided with the DatabaseValue type:

let row = try Row.fetchOne(db, sql: "SELECT 'syrah'")!

row[0] as String  // "syrah"
row[0] as Grape?  // fatal error: could not convert "syrah" to Grape.
row[0] as Grape   // fatal error: could not convert "syrah" to Grape.

let dbValue: DatabaseValue = row[0]
if dbValue.isNull {
    // Handle NULL
} else if let grape = Grape.fromDatabaseValue(dbValue) {
    // Handle valid grape
} else {
    // Handle unknown grape
}

Custom Value Types

Conversion to and from the database is based on the DatabaseValueConvertible protocol:

protocol DatabaseValueConvertible {
    /// Returns a value that can be stored in the database.
    var databaseValue: DatabaseValue { get }

    /// Returns a value initialized from dbValue, if possible.
    static func fromDatabaseValue(_ dbValue: DatabaseValue) -> Self?
}

All types that adopt this protocol can be used like all other values (Bool, Int, String, Date, Swift enums, etc.)

The databaseValue property returns DatabaseValue, a type that wraps the five values supported by SQLite: NULL, Int64, Double, String and Data. Since DatabaseValue has no public initializer, use DatabaseValue.null, or another type that already adopts the protocol: 1.databaseValue, "foo".databaseValue, etc. Conversion to DatabaseValue must not fail.

The fromDatabaseValue() factory method returns an instance of your custom type if the database value contains a suitable value. If the database value does not contain a suitable value, such as “foo” for Date, fromDatabaseValue must return nil (GRDB will interpret this nil result as a conversion error, and react accordingly).

Value types that adopt both DatabaseValueConvertible and an archival protocol (Codable, Encodable or Decodable) are automatically coded and decoded from JSON arrays and objects:

// Encoded as a JSON object in the database:
struct Color: Codable, DatabaseValueConvertible {
    var r: Double
    var g: Double
    var b: Double
}

For such codable value types, GRDB uses the standard JSONDecoder and JSONEncoder from Foundation. By default, Data values are handled with the .base64 strategy, Date with the .millisecondsSince1970 strategy, and non conforming floats with the .throw strategy.

In order to customize the JSON format, provide a custom implementation of the DatabaseValueConvertible requirements.

:point_up: Note: standard sequences such as Array, Set, or Dictionary do not conform to DatabaseValueConvertible, even conditionally. You won’t be able to directly fetch or store arrays, sets, or dictionaries as JSON database values. You can get free JSON support from these standard types when they are embedded as properties of Codable Records, though.

Transactions and Savepoints

• Transactions and Safety
• Explicit Transactions
• Savepoints
• Transaction Kinds

Transactions and Safety

A transaction is a fundamental tool of SQLite that guarantees data consistency as well as proper isolation between application threads and database connections.

GRDB generally opens transactions for you, as a way to enforce its concurrency guarantees, and provide maximal security for both your application data and application logic:

// BEGIN TRANSACTION
// INSERT INTO credit ...
// INSERT INTO debit ...
// COMMIT
try dbQueue.write { db in
    try Credit(destinationAccount, amount).insert(db)
    try Debit(sourceAccount, amount).insert(db)
}

// BEGIN TRANSACTION
// INSERT INTO credit ...
// INSERT INTO debit ...
// COMMIT
try dbPool.write { db in
    try Credit(destinationAccount, amount).insert(db)
    try Debit(sourceAccount, amount).insert(db)
}

Yet you may need to exactly control when transactions take place:

Explicit Transactions

DatabaseQueue.inDatabase() and DatabasePool.writeWithoutTransaction() execute your database statements outside of any transaction:

// INSERT INTO credit ...
// INSERT INTO debit ...
try dbQueue.inDatabase { db in
    try Credit(destinationAccount, amount).insert(db)
    try Debit(sourceAccount, amount).insert(db)
}

// INSERT INTO credit ...
// INSERT INTO debit ...
try dbPool.writeWithoutTransaction { db in
    try Credit(destinationAccount, amount).insert(db)
    try Debit(sourceAccount, amount).insert(db)
}

Writing outside of any transaction is dangerous, for two reasons:

• In our credit/debit example, you may successfully insert a credit, but fail inserting the debit, and end up with unbalanced accounts (oops).

  // UNSAFE DATABASE INTEGRITY
  try dbQueue.inDatabase { db in // or dbPool.writeWithoutTransaction
      try Credit(destinationAccount, amount).insert(db) // may succeed
      try Debit(sourceAccount, amount).insert(db)      // may fail
  }
  

  Transactions avoid this kind of bug.

• Database pool concurrent reads can see an inconsistent state of the database:

  // UNSAFE CONCURRENCY
  try dbPool.writeWithoutTransaction { db in
      try Credit(destinationAccount, amount).insert(db)
      // <- Concurrent dbPool.read sees a partial db update here
      try Debit(sourceAccount, amount).insert(db)
  }
  

  Transactions avoid this kind of bug, too.

To open explicit transactions, use one of the Database.inTransaction, DatabaseQueue.inTransaction, or DatabasePool.writeInTransaction methods:

// BEGIN TRANSACTION
// INSERT INTO credit ...
// INSERT INTO debit ...
// COMMIT
try dbQueue.inDatabase { db in  // or dbPool.writeWithoutTransaction
    try db.inTransaction {
        try Credit(destinationAccount, amount).insert(db)
        try Debit(sourceAccount, amount).insert(db)
        return .commit
    }
}

// BEGIN TRANSACTION
// INSERT INTO credit ...
// INSERT INTO debit ...
// COMMIT
try dbQueue.inTransaction { db in  // or dbPool.writeInTransaction
    try Credit(destinationAccount, amount).insert(db)
    try Debit(sourceAccount, amount).insert(db)
    return .commit
}

If an error is thrown from the transaction block, the transaction is rollbacked and the error is rethrown by the inTransaction method. If you return .rollback instead of .commit, the transaction is also rollbacked, but no error is thrown.

You can also perform manual transaction management:

try dbQueue.inDatabase { db in  // or dbPool.writeWithoutTransaction
    try db.beginTransaction()
    ...
    try db.commit()

    try db.execute(sql: "BEGIN TRANSACTION")
    ...
    try db.execute(sql: "ROLLBACK")
}

Transactions can’t be left opened unless you set the allowsUnsafeTransactions configuration flag:

// fatal error: A transaction has been left opened at the end of a database access
try dbQueue.inDatabase { db in
    try db.execute(sql: "BEGIN TRANSACTION")
    // <- no commit or rollback
}

You can ask if a transaction is currently opened:

func myCriticalMethod(_ db: Database) throws {
    precondition(db.isInsideTransaction, "This method requires a transaction")
    try ...
}

Yet, you have a better option than checking for transactions: critical database sections should use savepoints, described below:

func myCriticalMethod(_ db: Database) throws {
    try db.inSavepoint {
        // Here the database is guaranteed to be inside a transaction.
        try ...
    }
}

Savepoints

Statements grouped in a savepoint can be rollbacked without invalidating a whole transaction:

try dbQueue.write { db in
    // Makes sure both inserts succeed, or none:
    try db.inSavepoint {
        try Credit(destinationAccount, amount).insert(db)
        try Debit(sourceAccount, amount).insert(db)
        return .commit
    }

    // Other savepoints, etc...
}

If an error is thrown from the savepoint block, the savepoint is rollbacked and the error is rethrown by the inSavepoint method. If you return .rollback instead of .commit, the savepoint is also rollbacked, but no error is thrown.

Unlike transactions, savepoints can be nested. They implicitly open a transaction if no one was opened when the savepoint begins. As such, they behave just like nested transactions. Yet the database changes are only written to disk when the outermost transaction is committed:

try dbQueue.inDatabase { db in
    try db.inSavepoint {
        ...
        try db.inSavepoint {
            ...
            return .commit
        }
        ...
        return .commit  // writes changes to disk
    }
}

SQLite savepoints are more than nested transactions, though. For advanced uses, use SQLite savepoint documentation.

Transaction Kinds

SQLite supports three kinds of transactions: deferred (the default), immediate, and exclusive.

The transaction kind can be changed in the database configuration, or for each transaction:

// 1) Default configuration:
let dbQueue = try DatabaseQueue(path: "...")

// BEGIN DEFERRED TRANSACTION ...
dbQueue.write { db in ... }

// BEGIN EXCLUSIVE TRANSACTION ...
dbQueue.inTransaction(.exclusive) { db in ... }

// 2) Customized default transaction kind:
var config = Configuration()
config.defaultTransactionKind = .immediate
let dbQueue = try DatabaseQueue(path: "...", configuration: config)

// BEGIN IMMEDIATE TRANSACTION ...
dbQueue.write { db in ... }

// BEGIN EXCLUSIVE TRANSACTION ...
dbQueue.inTransaction(.exclusive) { db in ... }

Prepared Statements

Prepared Statements let you prepare an SQL query and execute it later, several times if you need, with different arguments.

try dbQueue.write { db in
    let insertSQL = "INSERT INTO player (name, score) VALUES (:name, :score)"
    let insertStatement = try db.makeStatement(sql: insertSQL)

    let selectSQL = "SELECT * FROM player WHERE name = ?"
    let selectStatement = try db.makeStatement(sql: selectSQL)
}

The ? and colon-prefixed keys like :name in the SQL query are the statement arguments. You set them with arrays or dictionaries (arguments are actually of type StatementArguments, which happens to adopt the ExpressibleByArrayLiteral and ExpressibleByDictionaryLiteral protocols).

insertStatement.arguments = ["name": "Arthur", "score": 1000]
selectStatement.arguments = ["Arthur"]

Alternatively, you can create a prepared statement with SQL Interpolation:

let insertStatement = try db.makeStatement(literal: "INSERT ...")
let selectStatement = try db.makeStatement(literal: "SELECT ...")
//                                         ~~~~~~~

Statements can be executed:

try insertStatement.execute()

Statements can be used wherever a raw SQL query string would fit (see fetch queries):

let rows = try Row.fetchCursor(selectStatement)    // A Cursor of Row
let players = try Player.fetchAll(selectStatement) // [Player]
let players = try Player.fetchSet(selectStatement) // Set<Player>
let player = try Player.fetchOne(selectStatement)  // Player?

You can set the arguments at the moment of the statement execution:

try insertStatement.execute(arguments: ["name": "Arthur", "score": 1000])
let player = try Player.fetchOne(selectStatement, arguments: ["Arthur"])

When you want to build multiple statements joined with a semicolon, use the allStatements method:

let statements = try db.allStatements(sql: """
    INSERT INTO player (name, score) VALUES (?, ?);
    INSERT INTO player (name, score) VALUES (?, ?);
    """, arguments: ["Arthur", 100, "O'Brien", 1000])
while let statement = try statements.next() {
    try statement.execute()
}

allStatements also supports SQL Interpolation:

let statements = try db.allStatements(literal: """
    INSERT INTO player (name, score) VALUES (\("Arthur"), \(100));
    INSERT INTO player (name, score) VALUES (\("O'Brien"), \(1000));
    """)
while let statement = try statements.next() {
    try statement.execute()
}

You can turn the cursor returned from allStatements into a regular Swift array, but in this case make sure all individual statements can compile even if the previous ones were not run:

// OK: Array of statements
let statements = try Array(db.allStatements(sql: """
    INSERT ...; 
    UPDATE ...; 
    SELECT ...;
    """))

// FAILURE: Can't build an array of statements since 
// the INSERT won't compile until CREATE TABLE is run.
let statements = try Array(db.allStatements(sql: """
    CREATE TABLE player ...; 
    INSERT INTO player ...;
    """))

See also Database.execute(sql:) in the Executing Updates chapter.

:point_up: Note: it is a programmer error to reuse a prepared statement that has failed: GRDB may crash if you do so.

For more information about prepared statements, see the Statement reference.

Prepared Statements Cache

When the same query will be used several times in the lifetime of your application, you may feel a natural desire to cache prepared statements.

Don’t cache statements yourself.

:point_up: Note: This is because you don’t have the necessary tools. Statements are tied to specific SQLite connections and dispatch queues which you don’t manage yourself, especially when you use database pools. A change in the database schema may, or may not invalidate a statement.

Instead, use the cachedStatement method. GRDB does all the hard caching and memory management stuff for you:

let statement = try db.cachedStatement(sql: sql)

Cached statements also support SQL Interpolation:

let statement = try db.cachedStatement(literal: "INSERT ...")
//                                     ~~~~~~~

:warning: Warning: Should a cached prepared statement throw an error, don’t reuse it (it is a programmer error). Instead, reload one from the cache.

Custom SQL Functions and Aggregates

SQLite lets you define SQL functions and aggregates.

A custom SQL function or aggregate extends SQLite:

SELECT reverse(name) FROM player;   -- custom function
SELECT maxLength(name) FROM player; -- custom aggregate

• Custom SQL Functions
• Custom Aggregates

Custom SQL Functions

A function argument takes an array of DatabaseValue, and returns any valid value (Bool, Int, String, Date, Swift enums, etc.) The number of database values is guaranteed to be argumentCount.

SQLite has the opportunity to perform additional optimizations when functions are “pure”, which means that their result only depends on their arguments. So make sure to set the pure argument to true when possible.

let reverse = DatabaseFunction("reverse", argumentCount: 1, pure: true) { (values: [DatabaseValue]) in
    // Extract string value, if any...
    guard let string = String.fromDatabaseValue(values[0]) else {
        return nil
    }
    // ... and return reversed string:
    return String(string.reversed())
}

You make a function available to a database connection through its configuration:

var config = Configuration()
config.prepareDatabase { db in
    db.add(function: reverse)
}
let dbQueue = try DatabaseQueue(path: dbPath, configuration: config)

try dbQueue.read { db in
    // "oof"
    try String.fetchOne(db, sql: "SELECT reverse('foo')")!
}

Functions can take a variable number of arguments:

When you don’t provide any explicit argumentCount, the function can take any number of arguments:

let averageOf = DatabaseFunction("averageOf", pure: true) { (values: [DatabaseValue]) in
    let doubles = values.compactMap { Double.fromDatabaseValue($0) }
    return doubles.reduce(0, +) / Double(doubles.count)
}
db.add(function: averageOf)

// 2.0
try Double.fetchOne(db, sql: "SELECT averageOf(1, 2, 3)")!

Functions can throw:

let sqrt = DatabaseFunction("sqrt", argumentCount: 1, pure: true) { (values: [DatabaseValue]) in
    guard let double = Double.fromDatabaseValue(values[0]) else {
        return nil
    }
    guard double >= 0 else {
        throw DatabaseError(message: "invalid negative number")
    }
    return sqrt(double)
}
db.add(function: sqrt)

// SQLite error 1 with statement `SELECT sqrt(-1)`: invalid negative number
try Double.fetchOne(db, sql: "SELECT sqrt(-1)")!

Use custom functions in the query interface:

// SELECT reverseString("name") FROM player
Player.select(reverseString(nameColumn))

GRDB ships with built-in SQL functions that perform unicode-aware string transformations. See Unicode.

Custom Aggregates

Before registering a custom aggregate, you need to define a type that adopts the DatabaseAggregate protocol:

protocol DatabaseAggregate {
    // Initializes an aggregate
    init()

    // Called at each step of the aggregation
    mutating func step(_ dbValues: [DatabaseValue]) throws

    // Returns the final result
    func finalize() throws -> DatabaseValueConvertible?
}

For example:

struct MaxLength : DatabaseAggregate {
    var maxLength: Int = 0

    mutating func step(_ dbValues: [DatabaseValue]) {
        // At each step, extract string value, if any...
        guard let string = String.fromDatabaseValue(dbValues[0]) else {
            return
        }
        // ... and update the result
        let length = string.count
        if length > maxLength {
            maxLength = length
        }
    }

    func finalize() -> DatabaseValueConvertible? {
        maxLength
    }
}

let maxLength = DatabaseFunction(
    "maxLength",
    argumentCount: 1,
    pure: true,
    aggregate: MaxLength.self)

Like custom SQL Functions, you make an aggregate function available to a database connection through its configuration:

var config = Configuration()
config.prepareDatabase { db in
    db.add(function: maxLength)
}
let dbQueue = try DatabaseQueue(path: dbPath, configuration: config)

try dbQueue.read { db in
    // Some Int
    try Int.fetchOne(db, sql: "SELECT maxLength(name) FROM player")!
}

The step method of the aggregate takes an array of DatabaseValue. This array contains as many values as the argumentCount parameter (or any number of values, when argumentCount is omitted).

The finalize method of the aggregate returns the final aggregated value (Bool, Int, String, Date, Swift enums, etc.).

SQLite has the opportunity to perform additional optimizations when aggregates are “pure”, which means that their result only depends on their inputs. So make sure to set the pure argument to true when possible.

Use custom aggregates in the query interface:

// SELECT maxLength("name") FROM player
let request = Player.select(maxLength.apply(nameColumn))
try Int.fetchOne(db, request) // Int?

Database Schema Introspection

GRDB comes with a set of schema introspection methods:

try dbQueue.read { db in
    // Bool, true if the table exists
    try db.tableExists("player")

    // [ColumnInfo], the columns in the table
    try db.columns(in: "player")

    // PrimaryKeyInfo
    try db.primaryKey("player")

    // [ForeignKeyInfo], the foreign keys defined on the table
    try db.foreignKeys(on: "player")

    // [IndexInfo], the indexes defined on the table
    try db.indexes(on: "player")

    // Bool, true if column(s) is a unique key (primary key or unique index)
    try db.table("player", hasUniqueKey: ["email"])
}

// Bool, true if argument is the name of an internal SQLite table
Database.isSQLiteInternalTable(...)

// Bool, true if argument is the name of an internal GRDB table
Database.isGRDBInternalTable(...)

Row Adapters

Row adapters let you present database rows in the way expected by the row consumers.

They basically help two incompatible row interfaces to work together. For example, a row consumer expects a column named “consumed”, but the produced row has a column named “produced”.

In this case, the ColumnMapping row adapter comes in handy:

// Turn the 'produced' column into 'consumed':
let adapter = ColumnMapping(["consumed": "produced"])
let row = try Row.fetchOne(db, sql: "SELECT 'Hello' AS produced", adapter: adapter)!

// [consumed:"Hello"]
print(row)

// "Hello"
print(row["consumed"])

// ▿ [consumed:"Hello"]
//   unadapted: [produced:"Hello"]
print(row.debugDescription)

// [produced:"Hello"]
print(row.unadapted)

Record types are typical row consumers that expect database rows to have a specific layout so that they can decode them:

struct MyRecord: Decodable, FetchableRecord {
    var consumed: String
}
let record = try MyRecord.fetchOne(db, sql: "SELECT 'Hello' AS produced", adapter: adapter)!
print(record.consumed) // "Hello"

There are several situations where row adapters are useful:

• They help disambiguate columns with identical names, which may happen when you select columns from several tables. See Joined Queries Support for an example.

• They help when SQLite outputs unexpected column names, which may happen with some subqueries. See RenameColumnAdapter for an example.

Available row adapters are described below.

• ColumnMapping
• EmptyRowAdapter
• RangeRowAdapter
• RenameColumnAdapter
• ScopeAdapter
• SuffixRowAdapter

ColumnMapping

ColumnMapping renames columns. Build one with a dictionary whose keys are adapted column names, and values the column names in the raw row:

// [newA:0, newB:1]
let adapter = ColumnMapping(["newA": "a", "newB": "b"])
let row = try Row.fetchOne(db, sql: "SELECT 0 AS a, 1 AS b, 2 AS c", adapter: adapter)!

Note that columns that are not present in the dictionary are not present in the resulting adapted row.

EmptyRowAdapter

EmptyRowAdapter hides all columns.

let adapter = EmptyRowAdapter()
let row = try Row.fetchOne(db, sql: "SELECT 0 AS a, 1 AS b, 2 AS c", adapter: adapter)!
row.isEmpty // true

This limit adapter may turn out useful in some narrow use cases. You’ll be happy to find it when you need it.

RangeRowAdapter

RangeRowAdapter only exposes a range of columns.

// [b:1]
let adapter = RangeRowAdapter(1..<2)
let row = try Row.fetchOne(db, sql: "SELECT 0 AS a, 1 AS b, 2 AS c", adapter: adapter)!

RenameColumnAdapter

RenameColumnAdapter lets you transform column names with a function:

// [arrr:0, brrr:1, crrr:2]
let adapter = RenameColumnAdapter { column in column + "rrr" }
let row = try Row.fetchOne(db, sql: "SELECT 0 AS a, 1 AS b, 2 AS c", adapter: adapter)!

This adapter may turn out useful, for example, when subqueries contain duplicated column names:

let sql = "SELECT * FROM (SELECT 1 AS id, 2 AS id)"

// Prints ["id", "id:1"]
// Note the "id:1" column, generated by SQLite.
let row = try Row.fetchOne(db, sql: sql)!
print(Array(row.columnNames))

// Drop the `:...` suffix, and prints ["id", "id"]
let adapter = RenameColumnAdapter { String($0.prefix(while: { $0 != ":" })) }
let adaptedRow = try Row.fetchOne(db, sql: sql, adapter: adapter)!
print(Array(adaptedRow.columnNames))

ScopeAdapter

ScopeAdapter defines row scopes:

let adapter = ScopeAdapter([
    "left": RangeRowAdapter(0..<2),
    "right": RangeRowAdapter(2..<4)])
let row = try Row.fetchOne(db, sql: "SELECT 0 AS a, 1 AS b, 2 AS c, 3 AS d", adapter: adapter)!

ScopeAdapter does not change the columns and values of the fetched row. Instead, it defines scopes, which you access through the Row.scopes property:

row                   // [a:0 b:1 c:2 d:3]
row.scopes["left"]    // [a:0 b:1]
row.scopes["right"]   // [c:2 d:3]
row.scopes["missing"] // nil

Scopes can be nested:

let adapter = ScopeAdapter([
    "left": ScopeAdapter([
        "left": RangeRowAdapter(0..<1),
        "right": RangeRowAdapter(1..<2)]),
    "right": ScopeAdapter([
        "left": RangeRowAdapter(2..<3),
        "right": RangeRowAdapter(3..<4)])
    ])
let row = try Row.fetchOne(db, sql: "SELECT 0 AS a, 1 AS b, 2 AS c, 3 AS d", adapter: adapter)!

let leftRow = row.scopes["left"]!
leftRow.scopes["left"]  // [a:0]
leftRow.scopes["right"] // [b:1]

let rightRow = row.scopes["right"]!
rightRow.scopes["left"]  // [c:2]
rightRow.scopes["right"] // [d:3]

Any adapter can be extended with scopes:

let baseAdapter = RangeRowAdapter(0..<2)
let adapter = ScopeAdapter(base: baseAdapter, scopes: [
    "remainder": SuffixRowAdapter(fromIndex: 2)])
let row = try Row.fetchOne(db, sql: "SELECT 0 AS a, 1 AS b, 2 AS c, 3 AS d", adapter: adapter)!

row // [a:0 b:1]
row.scopes["remainder"] // [c:2 d:3]

To see how ScopeAdapter can be used, see Joined Queries Support.

SuffixRowAdapter

SuffixRowAdapter hides the first columns in a row:

// [b:1 c:2]
let adapter = SuffixRowAdapter(fromIndex: 1)
let row = try Row.fetchOne(db, sql: "SELECT 0 AS a, 1 AS b, 2 AS c", adapter: adapter)!

Raw SQLite Pointers

If not all SQLite APIs are exposed in GRDB, you can still use the SQLite C Interface and call SQLite C functions.

Those functions are embedded right into the GRDB module, regardless of the underlying SQLite implementation (system SQLite, SQLCipher, or custom SQLite build):

import GRDB

let sqliteVersion = String(cString: sqlite3_libversion())

Raw pointers to database connections and statements are available through the Database.sqliteConnection and Statement.sqliteStatement properties:

try dbQueue.read { db in
    // The raw pointer to a database connection:
    let sqliteConnection = db.sqliteConnection

    // The raw pointer to a statement:
    let statement = try db.makeStatement(sql: "SELECT ...")
    let sqliteStatement = statement.sqliteStatement
}

:point_up: Notes

• Those pointers are owned by GRDB: don’t close connections or finalize statements created by GRDB.
• GRDB opens SQLite connections in the “multi-thread mode”, which (oddly) means that they are not thread-safe. Make sure you touch raw databases and statements inside their dedicated dispatch queues.
• Use the raw SQLite C Interface at your own risk. GRDB won’t prevent you from shooting yourself in the foot.

Records

On top of the SQLite API, GRDB provides protocols and a class that help manipulating database rows as regular objects named “records”:

try dbQueue.write { db in
    if var place = try Place.fetchOne(db, id: 1) {
        place.isFavorite = true
        try place.update(db)
    }
}

Of course, you need to open a database connection, and create database tables first.

To define your custom records, you subclass the ready-made Record class, or you extend your structs and classes with protocols that come with focused sets of features: fetching methods, persistence methods, record comparison…

Extending structs with record protocols is more “swifty”. Subclassing the Record class is more “classic”. You can choose either way. See some examples of record definitions, and the list of record methods for an overview.

:point_up: Note: if you are familiar with Core Data’s NSManagedObject or Realm’s Object, you may experience a cultural shock: GRDB records are not uniqued, do not auto-update, and do not lazy-load. This is both a purpose, and a consequence of protocol-oriented programming. You should read How to build an iOS application with SQLite and GRDB.swift for a general introduction.

:bulb: Tip: after you have read this chapter, check the Good Practices for Designing Record Types Guide.

:bulb: Tip: see the Demo Applications for sample apps that uses records.

Overview

• Inserting Records
• Fetching Records
• Updating Records
• Deleting Records
• Counting Records

Protocols and the Record Class

• Record Protocols Overview
• FetchableRecord Protocol
• TableRecord Protocol
• PersistableRecord Protocol
  • Persistence Methods
  • Customizing the Persistence Methods
• Identifiable Records
• Codable Records
• Record Class
• Record Comparison
• Record Customization Options

Records in a Glance

• Examples of Record Definitions
• List of Record Methods

Inserting Records

To insert a record in the database, call the insert method:

let player = Player(name: "Arthur", email: "arthur@example.com")
try player.insert(db)

:point_right: insert is available for subclasses of the Record class, and types that adopt the PersistableRecord protocol.

Fetching Records

To fetch records from the database, call a fetching method:

let arthur = try Player.fetchOne(db,            // Player?
    sql: "SELECT * FROM players WHERE name = ?",
    arguments: ["Arthur"])

let bestPlayers = try Player                    // [Player]
    .order(Column("score").desc)
    .limit(10)
    .fetchAll(db)

let spain = try Country.fetchOne(db, id: "ES")  // Country?

:point_right: Fetching from raw SQL is available for subclasses of the Record class, and types that adopt the FetchableRecord protocol.

:point_right: Fetching without SQL, using the query interface, is available for subclasses of the Record class, and types that adopt both FetchableRecord and TableRecord protocol.

Updating Records

To update a record in the database, call the update method:

var player: Player = ...
player.score = 1000
try player.update(db)

It is possible to avoid useless updates:

// does not hit the database if score has not changed
try player.updateChanges(db) {
    $0.score = 1000
}

See the query interface for batch updates:

try Player
    .filter(Column("team") == "red")
    .updateAll(db, Column("score") += 1)

:point_right: update methods are available for subclasses of the Record class, and types that adopt the PersistableRecord protocol. Batch updates are available on the TableRecord protocol.

Deleting Records

To delete a record in the database, call the delete method:

let player: Player = ...
try player.delete(db)

You can also delete by primary key, unique key, or perform batch deletes (see Delete Requests):

try Player.deleteOne(db, id: 1)
try Player.deleteOne(db, key: ["email": "arthur@example.com"])
try Country.deleteAll(db, ids: ["FR", "US"])
try Player
    .filter(Column("email") == nil)
    .deleteAll(db)

:point_right: delete methods are available for subclasses of the Record class, and types that adopt the PersistableRecord protocol. Batch deletes are available on the TableRecord protocol.

Counting Records

To count records, call the fetchCount method:

let playerCount: Int = try Player.fetchCount(db)

let playerWithEmailCount: Int = try Player
    .filter(Column("email") == nil)
    .fetchCount(db)

:point_right: fetchCount is available for subclasses of the Record class, and types that adopt the TableRecord protocol.

Details follow:

• Record Protocols Overview
• FetchableRecord Protocol
• TableRecord Protocol
• PersistableRecord Protocol
• Identifiable Records
• Codable Records
• Record Class
• Record Comparison
• Record Customization Options
• Examples of Record Definitions
• List of Record Methods

Record Protocols Overview

GRDB ships with three record protocols. Your own types will adopt one or several of them, according to the abilities you want to extend your types with.

• FetchableRecord is able to decode database rows.

  struct Place: FetchableRecord { ... }
  let places = try dbQueue.read { db in
      try Place.fetchAll(db, sql: "SELECT * FROM place")
  }
  

  :bulb: Tip: FetchableRecord can derive its implementation from the standard Decodable protocol. See Codable Records for more information.

  FetchableRecord can decode database rows, but it is not able to build SQL requests for you. For that, you also need TableRecord:

• TableRecord is able to generate SQL queries:

  struct Place: TableRecord { ... }
  let placeCount = try dbQueue.read { db in
      // Generates and runs `SELECT COUNT(*) FROM place`
      try Place.fetchCount(db)
  }
  

  When a type adopts both TableRecord and FetchableRecord, it can load from those requests:

  struct Place: TableRecord, FetchableRecord { ... }
  try dbQueue.read { db in
      let places = try Place.order(Column("title")).fetchAll(db)
      let paris = try Place.fetchOne(id: 1)
  }
  

• PersistableRecord is able to write: it can create, update, and delete rows in the database:

  struct Place : PersistableRecord { ... }
  try dbQueue.write { db in
      try Place.delete(db, id: 1)
      try Place(...).insert(db)
  }
  

  A persistable record can also compare itself against other records, and avoid useless database updates.

  :bulb: Tip: PersistableRecord can derive its implementation from the standard Encodable protocol. See Codable Records for more information.

FetchableRecord Protocol

The FetchableRecord protocol grants fetching methods to any type that can be built from a database row:

protocol FetchableRecord {
    /// Row initializer
    init(row: Row)
}

To use FetchableRecord, subclass the Record class, or adopt it explicitly. For example:

struct Place {
    var id: Int64?
    var title: String
    var coordinate: CLLocationCoordinate2D
}

extension Place : FetchableRecord {
    init(row: Row) {
        id = row["id"]
        title = row["title"]
        coordinate = CLLocationCoordinate2D(
            latitude: row["latitude"],
            longitude: row["longitude"])
    }
}

Rows also accept column enums:

extension Place : FetchableRecord {
    enum Columns: String, ColumnExpression {
        case id, title, latitude, longitude
    }

    init(row: Row) {
        id = row[Columns.id]
        title = row[Columns.title]
        coordinate = CLLocationCoordinate2D(
            latitude: row[Columns.latitude],
            longitude: row[Columns.longitude])
    }
}

See column values for more information about the row[] subscript.

When your record type adopts the standard Decodable protocol, you don’t have to provide the implementation for init(row:). See Codable Records for more information:

// That's all
struct Player: Decodable, FetchableRecord {
    var id: Int64
    var name: String
    var score: Int
}

FetchableRecord allows adopting types to be fetched from SQL queries:

try Place.fetchCursor(db, sql: "SELECT ...", arguments:...) // A Cursor of Place
try Place.fetchAll(db, sql: "SELECT ...", arguments:...)    // [Place]
try Place.fetchSet(db, sql: "SELECT ...", arguments:...)    // Set<Place>
try Place.fetchOne(db, sql: "SELECT ...", arguments:...)    // Place?

See fetching methods for information about the fetchCursor, fetchAll, fetchSet and fetchOne methods. See StatementArguments for more information about the query arguments.

:point_up: Note: for performance reasons, the same row argument to init(row:) is reused during the iteration of a fetch query. If you want to keep the row for later use, make sure to store a copy: self.row = row.copy().

:point_up: Note: The FetchableRecord.init(row:) initializer fits the needs of most applications. But some application are more demanding than others. When FetchableRecord does not exactly provide the support you need, have a look at the Beyond FetchableRecord chapter.

TableRecord Protocol

The TableRecord protocol generates SQL for you. To use TableRecord, subclass the Record class, or adopt it explicitly:

protocol TableRecord {
    static var databaseTableName: String { get }
    static var databaseSelection: [SQLSelectable] { get }
}

The databaseSelection type property is optional, and documented in the Columns Selected by a Request chapter.

The databaseTableName type property is the name of a database table. By default, it is derived from the type name:

struct Place: TableRecord { }
print(Place.databaseTableName) // prints "place"

For example:

• Place: place
• Country: country
• PostalAddress: postalAddress
• HTTPRequest: httpRequest
• TOEFL: toefl

You can still provide a custom table name:

struct Place: TableRecord {
    static let databaseTableName = "location"
}
print(Place.databaseTableName) // prints "location"

Subclasses of the Record class must always override their superclass’s databaseTableName property:

class Place: Record {
    override class var databaseTableName: String { "place" }
}
print(Place.databaseTableName) // prints "place"

When a type adopts both TableRecord and FetchableRecord, it can be fetched using the query interface:

// SELECT * FROM place WHERE name = 'Paris'
let paris = try Place.filter(nameColumn == "Paris").fetchOne(db)

TableRecord can also fetch deal with primary and unique keys: see Fetching by Key and Testing for Record Existence.

PersistableRecord Protocol

GRDB record types can create, update, and delete rows in the database.

Those abilities are granted by three protocols:

// Defines how a record encodes itself into the database
protocol EncodableRecord {
    /// Defines the values persisted in the database
    func encode(to container: inout PersistenceContainer)
}

// Adds persistence methods
protocol MutablePersistableRecord: TableRecord, EncodableRecord {
    /// Optional method that lets your adopting type store its rowID upon
    /// successful insertion. Don't call it directly: it is called for you.
    mutating func didInsert(with rowID: Int64, for column: String?)
}

// Adds immutability
protocol PersistableRecord: MutablePersistableRecord {
    /// Non-mutating version of the optional didInsert(with:for:)
    func didInsert(with rowID: Int64, for column: String?)
}

Yes, three protocols instead of one. Here is how you pick one or the other:

• If your type is a class, choose PersistableRecord. On top of that, implement didInsert(with:for:) if the database table has an auto-incremented primary key.

• If your type is a struct, and the database table has an auto-incremented primary key, choose MutablePersistableRecord, and implement didInsert(with:for:).

• Otherwise, choose PersistableRecord, and ignore didInsert(with:for:).

The encode(to:) method defines which values (Bool, Int, String, Date, Swift enums, etc.) are assigned to database columns.

The optional didInsert method lets the adopting type store its rowID after successful insertion, and is only useful for tables that have an auto-incremented primary key. It is called from a protected dispatch queue, and serialized with all database updates.

To use the persistable protocols, subclass the Record class, or adopt one of them explicitly. For example:

extension Place : MutablePersistableRecord {
    /// The values persisted in the database
    func encode(to container: inout PersistenceContainer) {
        container["id"] = id
        container["title"] = title
        container["latitude"] = coordinate.latitude
        container["longitude"] = coordinate.longitude
    }

    // Update auto-incremented id upon successful insertion
    mutating func didInsert(with rowID: Int64, for column: String?) {
        id = rowID
    }
}

var paris = Place(
    id: nil,
    title: "Paris",
    coordinate: CLLocationCoordinate2D(latitude: 48.8534100, longitude: 2.3488000))

try paris.insert(db)
paris.id   // some value

Persistence containers also accept column enums:

extension Place : MutablePersistableRecord {
    enum Columns: String, ColumnExpression {
        case id, title, latitude, longitude
    }

    func encode(to container: inout PersistenceContainer) {
        container[Columns.id] = id
        container[Columns.title] = title
        container[Columns.latitude] = coordinate.latitude
        container[Columns.longitude] = coordinate.longitude
    }
}