zeus
127 lines
3.2 KiB
Swift
127 lines
3.2 KiB
Swift
/// A type that represents a column in a database table.
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///
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/// ## Topics
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///
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/// ### Standard Columns
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///
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/// - ``rowID``
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///
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/// ### Deriving SQL Expressions
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///
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/// - ``detached``
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/// - ``match(_:)-727nk``
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/// - ``match(_:)-1vvo8``
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///
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/// ### Creating Column Assignments
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///
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/// - ``noOverwrite``
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/// - ``set(to:)``
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public protocol ColumnExpression: SQLSpecificExpressible {
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/// The column name.
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///
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/// The column name is never qualified with a table name.
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///
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/// For example, the name of a column can be `"score"`, but
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/// not `"player.score"`.
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var name: String { get }
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}
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extension ColumnExpression {
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/// Returns an SQL column.
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public var sqlExpression: SQLExpression {
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.column(name)
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}
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/// An SQL expression that refers to an aliased column
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/// (`expression AS alias`).
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///
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/// Once detached, a column is never qualified with any table name in the
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/// SQL generated by the query interface.
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///
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/// For example, see how `Column("total").detached` makes it possible to
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/// sort this query, when a raw `Column("total")` could not:
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///
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/// ```swift
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/// // SELECT player.*,
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/// // (player.score + player.bonus) AS total,
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/// // team.*
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/// // FROM player
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/// // JOIN team ON team.id = player.teamID
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/// // ORDER BY total, player.name
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/// // ~~~~~
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/// let request = Player
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/// .annotated(with: (Column("score") + Column("bonus")).forKey("total"))
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/// .including(required: Player.team)
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/// .order(Column("total").detached, Column("name"))
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/// ```
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public var detached: SQLExpression {
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SQL(sql: name.quotedDatabaseIdentifier).sqlExpression
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}
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}
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extension ColumnExpression where Self == Column {
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/// The hidden rowID column.
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public static var rowID: Self { Column.rowID }
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}
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/// A column in a database table.
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///
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/// For example:
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///
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/// ```swift
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/// struct Player: TableRecord {
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/// var score: Int
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/// }
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///
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/// let maximumScore = try dbQueue.read { db in
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/// // SELECT MAX(score) FROM player
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/// try Player
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/// .select(max(Column("score")), as: Int.self)
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/// .fetchOne(db)
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/// }
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/// ```
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///
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/// ## Topics
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///
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/// ### Standard Columns
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///
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/// - ``rowID-3bn70``
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/// - ``rank``
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///
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/// ### Creating A Column
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///
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/// - ``init(_:)-5grmu``
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/// - ``init(_:)-7xc4z``
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public struct Column: Sendable {
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/// The hidden rowID column.
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public static let rowID = Column("rowid")
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public var name: String
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/// Creates a `Column` given its name.
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///
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/// The name should be unqualified, such as `"score"`. Qualified name such
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/// as `"player.score"` are unsupported.
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public init(_ name: String) {
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self.name = name
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}
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/// Creates a `Column` given a `CodingKey`.
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public init(_ codingKey: some CodingKey) {
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self.name = codingKey.stringValue
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}
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}
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extension Column: ColumnExpression { }
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/// Support for column enums:
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///
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/// struct Player {
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/// enum Columns: String, ColumnExpression {
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/// case id, name, score
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/// }
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/// }
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extension ColumnExpression where Self: RawRepresentable, Self.RawValue == String {
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public var name: String { rawValue }
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}
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