add swiftUI code

iOS-SwiftUI-Code/GRDB.swift-6.29.3/GRDB/JSON/JSONColumn.swift

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+/// A JSON column in a database table.
+///
+/// ## Overview
+///
+/// `JSONColumn` has benefits over ``Column`` for database columns that
+/// contain JSON strings.
+///
+/// It behaves like a regular `Column`, with all extra conveniences and
+/// behaviors of ``SQLJSONExpressible``.
+///
+/// For example, the sample code below directly accesses the "countryCode"
+/// key of the "address" JSON column:
+///
+/// ```swift
+/// struct Player: Codable {
+///     var id: Int64
+///     var name: String
+///     var address: Address
+/// }
+///
+/// struct Address: Codable {
+///     var street: String
+///     var city: String
+///     var countryCode: String
+/// }
+///
+/// extension Player: FetchableRecord, PersistableRecord {
+///     enum Columns {
+///         static let id = Column(CodingKeys.id)
+///         static let name = Column(CodingKeys.name)
+///         static let address = JSONColumn(CodingKeys.address) // JSONColumn!
+///     }
+/// }
+///
+/// try dbQueue.write { db in
+///     // In a real app, table creation should happen in a migration.
+///     try db.create(table: "player") { t in
+///         t.autoIncrementedPrimaryKey("id")
+///         t.column("name", .text).notNull()
+///         t.column("address", .jsonText).notNull()
+///     }
+///
+///     // Fetch all country codes
+///     // SELECT DISTINCT address ->> 'countryCode' FROM player
+///     let countryCodes: [String] = try Player
+///         .select(Player.Columns.address["countryCode"], as: String.self)
+///         .distinct()
+///         .fetchAll(db)
+/// }
+/// ```
+///
+/// > Tip: When you can not create a `JSONColumn`, you'll get the same
+/// > convenient access to JSON subcomponents
+/// > with ``SQLSpecificExpressible/asJSON``.
+/// >
+/// > For example, the above sample can be adapted as below:
+/// >
+/// > ```swift
+/// > extension Player: FetchableRecord, PersistableRecord {
+/// >     // That's another valid way to define columns.
+/// >     // But we don't have any JSONColumn this time.
+/// >     enum Columns: String, ColumnExpression {
+/// >         case id, name, address
+/// >     }
+/// > }
+/// >
+/// > try dbQueue.write { db in
+/// >     // Fetch all country codes
+/// >     // SELECT DISTINCT address ->> 'countryCode' FROM player
+/// >     let countryCodes: [String] = try Player
+/// >         .select(Player.Columns.address.asJSON["countryCode"], as: String.self)
+/// >         .distinct()
+/// >         .fetchAll(db)
+/// > }
+/// > ```
+public struct JSONColumn: ColumnExpression, SQLJSONExpressible, Sendable {
+    public var name: String
+    
+    /// Creates a `JSONColumn` given its name.
+    ///
+    /// The name should be unqualified, such as `"score"`. Qualified name such
+    /// as `"player.score"` are unsupported.
+    public init(_ name: String) {
+        self.name = name
+    }
+    
+    /// Creates a `JSONColumn` given a `CodingKey`.
+    public init(_ codingKey: some CodingKey) {
+        self.name = codingKey.stringValue
+    }
+}