StatementColumnConvertible

public protocol StatementColumnConvertible

The StatementColumnConvertible protocol grants access to the low-level C interface that extracts values from query results: https://www.sqlite.org/c3ref/column_blob.html. It can bring performance improvements.

To use it, have a value type adopt both StatementColumnConvertible and DatabaseValueConvertible. GRDB will then automatically apply the optimization whenever direct access to SQLite is possible:

let rows = Row.fetchCursor(db, sql: "SELECT ...")
while let row = try rows.next() {
    let int: Int = row[0]                 // there
}
let ints = Int.fetchAll(db, sql: "SELECT ...") // there
struct Player {
    init(row: Row) {
        name = row["name"]                // there
        score = row["score"]              // there
    }
}

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                    init(sqliteStatement:index:)

Initializes a value from a raw SQLite statement pointer, if possible.

For example, here is the how Int64 adopts StatementColumnConvertible:

extension Int64: StatementColumnConvertible {
    init?(sqliteStatement: SQLiteStatement, index: Int32) {
        self = sqlite3_column_int64(sqliteStatement, index)
    }
}

This initializer is never called for NULL database values. Just return nil for failed conversions: GRDB will interpret a nil result as a decoding failure.

See https://www.sqlite.org/c3ref/column_blob.html for more information.

Declaration

Swift

init?(sqliteStatement: SQLiteStatement, index: Int32)

Parameters

`sqliteStatement`	A pointer to an SQLite statement.
`index`	The column index.

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