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17 changes: 14 additions & 3 deletions
17
Documentation/DemoApps/GRDBCombineDemo/GRDBCombineDemo/GRDBCombineDemoApp.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,12 +1,23 @@ | ||
| import GRDB | ||
| import SwiftUI | ||
|
|
||
| @main | ||
| struct GRDBCombineDemoApp: App { | ||
| let appDatabase = AppDatabase.shared | ||
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| var body: some Scene { | ||
| WindowGroup { | ||
| PlayerList(viewModel: PlayerListViewModel(database: appDatabase)) | ||
| AppView().environment(\.appDatabase, AppDatabase.shared) | ||
| } | ||
| } | ||
| } | ||
|
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| // Let SwiftUI views access the database through the SwiftUI environment | ||
| private struct AppDatabaseKey: EnvironmentKey { | ||
| static let defaultValue: AppDatabase? = nil | ||
| } | ||
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| extension EnvironmentValues { | ||
| var appDatabase: AppDatabase? { | ||
| get { self[AppDatabaseKey.self] } | ||
| set { self[AppDatabaseKey.self] = newValue } | ||
| } | ||
| } |
23 changes: 23 additions & 0 deletions
23
Documentation/DemoApps/GRDBCombineDemo/GRDBCombineDemo/PlayerRequest.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,23 @@ | ||
| import GRDB | ||
|
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| /// A player request defines how to feed the player list | ||
| struct PlayerRequest { | ||
| enum Ordering { | ||
| case byScore | ||
| case byName | ||
| } | ||
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| var ordering: Ordering | ||
| } | ||
|
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| /// Make `PlayerRequest` able to be used with the `@Query` property wrapper. | ||
| extension PlayerRequest: Queryable { | ||
| static var defaultValue: [Player] { [] } | ||
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| func fetchValue(_ db: Database) throws -> [Player] { | ||
| switch ordering { | ||
| case .byScore: return try Player.all().orderedByScore().fetchAll(db) | ||
| case .byName: return try Player.all().orderedByName().fetchAll(db) | ||
| } | ||
| } | ||
| } |
109 changes: 109 additions & 0 deletions
109
Documentation/DemoApps/GRDBCombineDemo/GRDBCombineDemo/Query.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,109 @@ | ||
| // | ||
| // Query.swift | ||
| // | ||
| // A property wrapper inspired from | ||
| // https://davedelong.com/blog/2021/04/03/core-data-and-swiftui/ | ||
| // | ||
|
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| import Combine | ||
| import GRDB | ||
| import SwiftUI | ||
|
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| /// The protocol that feeds the `@Query` property wrapper. | ||
| protocol Queryable: Equatable { | ||
| /// The type of the fetched value | ||
| associatedtype Value | ||
|
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| /// The default value, used whenever the database is not available | ||
| static var defaultValue: Value { get } | ||
|
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| /// Fetches the database value | ||
| func fetchValue(_ db: Database) throws -> Value | ||
| } | ||
|
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| /// The property wrapper that observes a database query | ||
| @propertyWrapper | ||
| struct Query<Query: Queryable>: DynamicProperty { | ||
| /// The database reader that makes it possible to observe the database | ||
| @Environment(\.appDatabase?.databaseReader) private var databaseReader: DatabaseReader? | ||
| @StateObject private var core = Core() | ||
| private var baseQuery: Query | ||
|
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| /// The fetched value | ||
| var wrappedValue: Query.Value { | ||
| core.value ?? Query.defaultValue | ||
| } | ||
|
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| /// A binding to the query, that lets your views modify it. | ||
| /// | ||
| /// This is how the demo app changes the player ordering. | ||
| var projectedValue: Binding<Query> { | ||
| Binding( | ||
| get: { core.query ?? baseQuery }, | ||
| set: { core.query = $0 }) | ||
| } | ||
|
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| init(_ query: Query) { | ||
| baseQuery = query | ||
| } | ||
|
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| func update() { | ||
| guard let databaseReader = databaseReader else { | ||
| fatalError("Attempting to use @Query without any database in the environment") | ||
| } | ||
| // Feed core with necessary information, and make sure tracking has started | ||
| if core.query == nil { core.query = baseQuery } | ||
| core.startTrackingIfNecessary(in: databaseReader) | ||
| } | ||
|
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| private class Core: ObservableObject { | ||
| private(set) var value: Query.Value? | ||
| var databaseReader: DatabaseReader? | ||
| var query: Query? { | ||
| willSet { | ||
| if query != newValue { | ||
| // Stop tracking, and tell SwiftUI about the update | ||
| objectWillChange.send() | ||
| cancellable = nil | ||
| } | ||
| } | ||
| } | ||
| private var cancellable: AnyCancellable? | ||
|
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| init() { } | ||
|
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| func startTrackingIfNecessary(in databaseReader: DatabaseReader) { | ||
| if databaseReader !== self.databaseReader { | ||
| // Database has changed. Stop tracking. | ||
| self.databaseReader = databaseReader | ||
| cancellable = nil | ||
| } | ||
|
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| guard let query = query else { | ||
| // No query set | ||
| return | ||
| } | ||
|
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| guard cancellable == nil else { | ||
| // Already tracking | ||
| return | ||
| } | ||
|
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| cancellable = ValueObservation | ||
| .tracking(query.fetchValue) | ||
| .publisher( | ||
| in: databaseReader, | ||
| scheduling: .immediate) | ||
| .sink( | ||
| receiveCompletion: { _ in | ||
| // Ignore errors | ||
| }, | ||
| receiveValue: { [weak self] value in | ||
| guard let self = self else { return } | ||
| // Tell SwiftUI about the new value | ||
| self.objectWillChange.send() | ||
| self.value = value | ||
| }) | ||
| } | ||
| } | ||
| } |
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