zeus
765 lines
28 KiB
Swift
765 lines
28 KiB
Swift
#if canImport(Combine)
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import Combine
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#endif
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import Dispatch
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/// A type that reads from an SQLite database.
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///
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/// Do not declare new conformances to `DatabaseReader`. Only the built-in
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/// conforming types are valid.
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///
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/// The protocol comes with isolation guarantees that describe the behavior of
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/// conforming types in a multithreaded application. See <doc:Concurrency> for
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/// more information.
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///
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/// ## Topics
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///
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/// ### Database Information
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///
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/// - ``configuration``
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/// - ``path``
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///
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/// ### Reading from the Database
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///
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/// - ``read(_:)-3806d``
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/// - ``read(_:)-4w6gy``
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/// - ``readPublisher(receiveOn:value:)``
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/// - ``asyncRead(_:)``
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///
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/// ### Unsafe Methods
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///
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/// - ``unsafeRead(_:)-5i7tf``
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/// - ``unsafeRead(_:)-11mk0``
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/// - ``unsafeReentrantRead(_:)``
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/// - ``asyncUnsafeRead(_:)``
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///
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/// ### Printing Database Content
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///
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/// - ``dumpContent(format:to:)``
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/// - ``dumpRequest(_:format:to:)``
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/// - ``dumpSchema(to:)``
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/// - ``dumpSQL(_:format:to:)``
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/// - ``dumpTables(_:format:tableHeader:stableOrder:to:)``
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/// - ``DumpFormat``
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/// - ``DumpTableHeaderOptions``
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///
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/// ### Other Database Operations
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///
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/// - ``backup(to:pagesPerStep:progress:)``
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/// - ``close()``
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/// - ``interrupt()``
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///
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/// ### Supporting Types
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///
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/// - ``AnyDatabaseReader``
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public protocol DatabaseReader: AnyObject, Sendable {
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/// The database configuration.
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var configuration: Configuration { get }
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/// The path to the database file.
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///
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/// In-memory databases also have a path:
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/// see [In-Memory Databases](https://www.sqlite.org/inmemorydb.html).
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var path: String { get }
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/// Closes the database connection.
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///
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/// - note: You do not have to call this method, and you should not call
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/// it unless the correct execution of your program depends on precise
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/// database closing. Database connections are automatically closed when
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/// they are deinitialized, and this is sufficient for most applications.
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///
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/// If this method does not throw, then the database is properly closed, and
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/// every future database access will throw a ``DatabaseError`` of
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/// code `SQLITE_MISUSE`.
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///
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/// Otherwise, there exists concurrent database accesses or living prepared
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/// statements that prevent the database from closing, and this method
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/// throws a ``DatabaseError`` of code `SQLITE_BUSY`.
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/// See <https://www.sqlite.org/c3ref/close.html> for more information.
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///
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/// After an error has been thrown, the database may still be opened, and
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/// you can keep on accessing it. It may also remain in a "zombie" state,
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/// in which case it will throw `SQLITE_MISUSE` for all future
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/// database accesses.
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///
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/// - throws: A ``DatabaseError`` whenever an SQLite error occurs.
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func close() throws
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// MARK: - Interrupting Database Operations
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/// Causes any pending database operation to abort and return at its
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/// earliest opportunity.
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///
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/// This method can be called from any thread.
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///
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/// A call to `interrupt()` that occurs when there are no running SQL
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/// statements is a no-op and has no effect on SQL statements that are
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/// started after `interrupt()` returns.
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///
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/// A database operation that is interrupted will throw a ``DatabaseError``
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/// with code `SQLITE_INTERRUPT`. If the interrupted SQL operation is an
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/// `INSERT`, `UPDATE`, or `DELETE` that is inside an explicit transaction,
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/// then the entire transaction will be rolled back automatically. If the
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/// rolled back transaction was started by a transaction-wrapping method
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/// such as ``DatabaseWriter/write(_:)-76inz`` or
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/// ``Database/inTransaction(_:_:)``, then all database accesses will throw
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/// a ``DatabaseError`` with code `SQLITE_ABORT` until the wrapping
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/// method returns.
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///
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/// For example:
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///
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/// ```swift
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/// try dbQueue.write { db in
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/// // interrupted:
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/// try Player(...).insert(db) // throws SQLITE_INTERRUPT
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/// // not executed:
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/// try Player(...).insert(db)
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/// } // throws SQLITE_INTERRUPT
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///
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/// try dbQueue.write { db in
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/// do {
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/// // interrupted:
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/// try Player(...).insert(db) // throws SQLITE_INTERRUPT
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/// } catch { }
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/// try Player(...).insert(db) // throws SQLITE_ABORT
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/// } // throws SQLITE_ABORT
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///
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/// try dbQueue.write { db in
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/// do {
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/// // interrupted:
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/// try Player(...).insert(db) // throws SQLITE_INTERRUPT
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/// } catch { }
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/// } // throws SQLITE_ABORT
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/// ```
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///
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/// Beware: when an application opens a transaction without a
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/// transaction-wrapping method, no `SQLITE_ABORT` error warns of
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/// aborted transactions:
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///
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/// ```swift
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/// try dbQueue.inDatabase { db in // or dbPool.writeWithoutTransaction
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/// try db.beginTransaction()
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/// do {
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/// // interrupted:
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/// try Player(...).insert(db) // throws SQLITE_INTERRUPT
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/// } catch { }
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/// try Player(...).insert(db) // success
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/// try db.commit() // throws SQLITE_ERROR "cannot commit - no transaction is active"
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/// }
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/// ```
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///
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/// Both `SQLITE_ABORT` and `SQLITE_INTERRUPT` errors can be checked with the
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/// ``DatabaseError/isInterruptionError`` property.
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func interrupt()
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// MARK: - Read From Database
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/// Executes read-only database operations, and returns their result after
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/// they have finished executing.
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///
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/// For example:
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///
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/// ```swift
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/// let count = try reader.read { db in
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/// try Player.fetchCount(db)
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/// }
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/// ```
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///
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/// Database operations are isolated in a transaction: they do not see
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/// changes performed by eventual concurrent writes (even writes performed
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/// by other processes).
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///
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/// The database connection is read-only: attempts to write throw a
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/// ``DatabaseError`` with resultCode `SQLITE_READONLY`.
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///
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/// The ``Database`` argument to `value` is valid only during the execution
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/// of the closure. Do not store or return the database connection for
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/// later use.
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///
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/// It is a programmer error to call this method from another database
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/// access method. Doing so raises a "Database methods are not reentrant"
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/// fatal error at runtime.
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///
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/// - parameter value: A closure which accesses the database.
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/// - throws: The error thrown by `value`, or any ``DatabaseError`` that
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/// would happen while establishing the database access.
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@_disfavoredOverload // SR-15150 Async overloading in protocol implementation fails
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func read<T>(_ value: (Database) throws -> T) throws -> T
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/// Schedules read-only database operations for execution, and
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/// returns immediately.
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///
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/// For example:
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///
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/// ```swift
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/// try reader.asyncRead { dbResult in
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/// do {
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/// let db = try dbResult.get()
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/// let count = try Player.fetchCount(db)
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/// } catch {
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/// // Handle error
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/// }
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/// }
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/// ```
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///
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/// Database operations are isolated in a transaction: they do not see
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/// changes performed by eventual concurrent writes (even writes performed
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/// by other processes).
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///
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/// The database connection is read-only: attempts to write throw a
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/// ``DatabaseError`` with resultCode `SQLITE_READONLY`.
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///
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/// - parameter value: A closure which accesses the database. Its argument
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/// is a `Result` that provides the database connection, or the failure
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/// that would prevent establishing the read access to the database.
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func asyncRead(_ value: @escaping (Result<Database, Error>) -> Void)
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/// Executes database operations, and returns their result after they have
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/// finished executing.
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///
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/// This method is "unsafe" because the database reader does nothing more
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/// than providing a database connection. When you use this method, you
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/// become responsible for the thread-safety of your application, and
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/// responsible for database accesses performed by other processes. See
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/// <doc:Concurrency#Safe-and-Unsafe-Database-Accesses> for
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/// more information.
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///
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/// For example:
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///
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/// ```swift
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/// let count = try reader.unsafeRead { db in
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/// try Player.fetchCount(db)
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/// }
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/// ```
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///
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/// The ``Database`` argument to `value` is valid only during the execution
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/// of the closure. Do not store or return the database connection for
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/// later use.
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///
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/// It is a programmer error to call this method from another database
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/// access method. Doing so raises a "Database methods are not reentrant"
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/// fatal error at runtime.
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///
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/// - warning: Database operations may not be wrapped in a transaction. They
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/// may see changes performed by concurrent writes or writes performed by
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/// other processes: two identical requests performed by the `value`
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/// closure may not return the same value.
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/// - warning: Attempts to write in the database may succeed.
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///
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/// - parameter value: A closure which accesses the database.
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/// - throws: The error thrown by `value`, or any ``DatabaseError`` that
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/// would happen while establishing the database access.
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@_disfavoredOverload // SR-15150 Async overloading in protocol implementation fails
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func unsafeRead<T>(_ value: (Database) throws -> T) throws -> T
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/// Schedules database operations for execution, and returns immediately.
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///
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/// This method is "unsafe" because the database reader does nothing more
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/// than providing a database connection. When you use this method, you
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/// become responsible for the thread-safety of your application, and
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/// responsible for database accesses performed by other processes. See
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/// <doc:Concurrency#Safe-and-Unsafe-Database-Accesses> for
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/// more information.
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///
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/// For example:
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///
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/// ```swift
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/// reader.asyncUnsafeRead { dbResult in
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/// do {
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/// let db = try dbResult.get()
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/// let count = try Player.fetchCount(db)
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/// } catch {
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/// // handle error
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/// }
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/// }
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/// ```
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///
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/// - warning: Database operations may not be wrapped in a transaction. They
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/// may see changes performed by concurrent writes or writes performed by
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/// other processes: two identical requests performed by the `value`
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/// closure may not return the same value.
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/// - warning: Attempts to write in the database may succeed.
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///
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/// - parameter value: A closure which accesses the database. Its argument
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/// is a `Result` that provides the database connection, or the failure
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/// that would prevent establishing the read access to the database.
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func asyncUnsafeRead(_ value: @escaping (Result<Database, Error>) -> Void)
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/// Executes database operations, and returns their result after they have
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/// finished executing.
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///
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/// This method is "unsafe" because the database reader does nothing more
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/// than providing a database connection. When you use this method, you
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/// become responsible for the thread-safety of your application, and
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/// responsible for database accesses performed by other processes. See
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/// <doc:Concurrency#Safe-and-Unsafe-Database-Accesses> for
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/// more information.
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///
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/// This method can be called from other database access methods. If called
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/// from the dispatch queue of a current database access (read or write),
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/// the `Database` argument to `value` is the same as the current
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/// database access.
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///
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/// Reentrant database accesses are discouraged because they muddle
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/// transaction boundaries
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/// (see <doc:Concurrency#Rule-2:-Mind-your-transactions> for
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/// more information).
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///
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/// For example:
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///
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/// ```swift
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/// let count = try reader.unsafeReentrantRead { db in
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/// try Player.fetchCount(db)
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/// }
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/// ```
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///
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/// The ``Database`` argument to `value` is valid only during the execution
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/// of the closure. Do not store or return the database connection for
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/// later use.
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///
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/// - warning: Database operations may not be wrapped in a transaction. They
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/// may see changes performed by concurrent writes or writes performed by
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/// other processes: two identical requests performed by the `value`
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/// closure may not return the same value.
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/// - warning: Attempts to write in the database may succeed.
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///
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/// - parameter value: A closure which accesses the database.
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/// - throws: The error thrown by `value`, or any ``DatabaseError`` that
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/// would happen while establishing the database access.
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func unsafeReentrantRead<T>(_ value: (Database) throws -> T) throws -> T
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// MARK: - Value Observation
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/// Starts a value observation.
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///
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/// Use the ``ValueObservation/start(in:scheduling:onError:onChange:)``
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/// method instead.
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///
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/// - parameter observation: a ValueObservation.
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/// - returns: A DatabaseCancellable that can stop the observation.
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func _add<Reducer: ValueReducer>(
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observation: ValueObservation<Reducer>,
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scheduling scheduler: some ValueObservationScheduler,
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onChange: @escaping (Reducer.Value) -> Void)
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-> AnyDatabaseCancellable
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}
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extension DatabaseReader {
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// MARK: - Backup
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/// Copies the database contents into another database.
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///
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/// The `backup` method blocks the current thread until the destination
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/// database contains the same contents as the source database.
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///
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/// When the source is a DatabasePool, concurrent writes can happen during
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/// the backup. Those writes may, or may not, be reflected in the backup,
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/// but they won't trigger any error.
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///
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/// Usage:
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///
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/// ```swift
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/// let source: DatabaseQueue = ...
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/// let destination: DatabaseQueue = ...
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/// try source.backup(to: destination)
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/// ```
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///
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/// When you're after progress reporting during backup, you'll want to
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/// perform the backup in several steps. Each step copies the number of
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/// _database pages_ you specify. See <https://www.sqlite.org/c3ref/backup_finish.html>
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/// for more information:
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///
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/// ```swift
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/// // Backup with progress reporting
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/// try source.backup(to: destination, pagesPerStep: ...) { progress in
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/// print("Database backup progress:", progress)
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/// }
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/// ```
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///
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/// The `progress` callback will be called at least once—when
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/// `backupProgress.isCompleted == true`. If the callback throws
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/// when `backupProgress.isCompleted == false`, the backup is aborted
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/// and the error is rethrown. If the callback throws when
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/// `backupProgress.isCompleted == true`, backup completion is
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/// unaffected and the error is silently ignored.
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///
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/// See also ``Database/backup(to:pagesPerStep:progress:)``
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///
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/// - parameters:
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/// - writer: The destination database.
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/// - pagesPerStep: The number of database pages copied on each backup
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/// step. By default, all pages are copied in one single step.
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/// - progress: An optional function that is notified of the backup
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/// progress.
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/// - throws: A ``DatabaseError`` whenever an SQLite error occurs, or the
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/// error thrown by `progress`.
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public func backup(
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to writer: some DatabaseWriter,
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pagesPerStep: CInt = -1,
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progress: ((DatabaseBackupProgress) throws -> Void)? = nil)
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throws
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{
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try writer.writeWithoutTransaction { destDb in
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try backup(
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to: destDb,
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pagesPerStep: pagesPerStep,
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afterBackupStep: progress)
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}
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}
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func backup(
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to destDb: Database,
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pagesPerStep: CInt = -1,
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afterBackupInit: (() -> Void)? = nil,
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afterBackupStep: ((DatabaseBackupProgress) throws -> Void)? = nil)
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throws
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{
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try read { dbFrom in
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try dbFrom.backupInternal(
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to: destDb,
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pagesPerStep: pagesPerStep,
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afterBackupInit: afterBackupInit,
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afterBackupStep: afterBackupStep)
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}
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}
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}
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extension DatabaseReader {
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// MARK: - Asynchronous Database Access
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/// Executes read-only database operations, and returns their result after
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/// they have finished executing.
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///
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/// - note: [**🔥 EXPERIMENTAL**](https://github.com/groue/GRDB.swift/blob/master/README.md#what-are-experimental-features)
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///
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/// For example:
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///
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/// ```swift
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/// let count = try await reader.read { db in
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/// try Player.fetchCount(db)
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/// }
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/// ```
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///
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/// Database operations are isolated in a transaction: they do not see
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/// changes performed by eventual concurrent writes (even writes performed
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/// by other processes).
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///
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/// The database connection is read-only: attempts to write throw a
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/// ``DatabaseError`` with resultCode `SQLITE_READONLY`.
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///
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/// The ``Database`` argument to `value` is valid only during the execution
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/// of the closure. Do not store or return the database connection for
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/// later use.
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///
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/// - parameter value: A closure which accesses the database.
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/// - throws: The error thrown by `value`, or any ``DatabaseError`` that
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/// would happen while establishing the database access.
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@available(iOS 13, macOS 10.15, tvOS 13, watchOS 6, *)
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public func read<T>(_ value: @Sendable @escaping (Database) throws -> T) async throws -> T {
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try await withUnsafeThrowingContinuation { continuation in
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asyncRead { result in
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do {
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try continuation.resume(returning: value(result.get()))
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} catch {
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continuation.resume(throwing: error)
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}
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}
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}
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}
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/// Executes database operations, and returns their result after they have
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/// finished executing.
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///
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/// - note: [**🔥 EXPERIMENTAL**](https://github.com/groue/GRDB.swift/blob/master/README.md#what-are-experimental-features)
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///
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/// This method is "unsafe" because the database reader does nothing more
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/// than providing a database connection. When you use this method, you
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/// become responsible for the thread-safety of your application, and
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/// responsible for database accesses performed by other processes. See
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/// <doc:Concurrency#Safe-and-Unsafe-Database-Accesses> for
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/// more information.
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///
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|
/// For example:
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///
|
|
/// ```swift
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/// let count = try await reader.unsafeRead { db in
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/// try Player.fetchCount(db)
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/// }
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/// ```
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///
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/// The ``Database`` argument to `value` is valid only during the execution
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/// of the closure. Do not store or return the database connection for
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/// later use.
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///
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/// - warning: Database operations may not be wrapped in a transaction. They
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/// may see changes performed by concurrent writes or writes performed by
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/// other processes: two identical requests performed by the `value`
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/// closure may not return the same value.
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/// - warning: Attempts to write in the database may succeed.
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///
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/// - parameter value: A closure which accesses the database.
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/// - throws: The error thrown by `value`, or any ``DatabaseError`` that
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/// would happen while establishing the database access.
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@available(iOS 13, macOS 10.15, tvOS 13, watchOS 6, *)
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|
public func unsafeRead<T>(_ value: @Sendable @escaping (Database) throws -> T) async throws -> T {
|
|
try await withUnsafeThrowingContinuation { continuation in
|
|
asyncUnsafeRead { result in
|
|
do {
|
|
try continuation.resume(returning: value(result.get()))
|
|
} catch {
|
|
continuation.resume(throwing: error)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
#if canImport(Combine)
|
|
extension DatabaseReader {
|
|
// MARK: - Publishing Database Values
|
|
|
|
/// Returns a publisher that publishes one value and completes.
|
|
///
|
|
/// The database is not accessed until subscription. Value and completion
|
|
/// are published on `scheduler` (the main dispatch queue by default).
|
|
///
|
|
/// For example:
|
|
///
|
|
/// ```swift
|
|
/// // DatabasePublishers.Read<Int>
|
|
/// let countPublisher = reader.readPublisher { db in
|
|
/// try Player.fetchCount(db)
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// Database operations are isolated in a transaction: they do not see
|
|
/// changes performed by eventual concurrent writes (even writes performed
|
|
/// by other processes).
|
|
///
|
|
/// The database connection is read-only: attempts to write throw a
|
|
/// ``DatabaseError`` with resultCode `SQLITE_READONLY`.
|
|
///
|
|
/// The ``Database`` argument to `value` is valid only during the execution
|
|
/// of the closure. Do not store or return the database connection for
|
|
/// later use.
|
|
///
|
|
/// - parameter scheduler: A Combine Scheduler.
|
|
/// - parameter value: A closure which accesses the database.
|
|
@available(iOS 13, macOS 10.15, tvOS 13, watchOS 6, *)
|
|
public func readPublisher<Output>(
|
|
receiveOn scheduler: some Combine.Scheduler = DispatchQueue.main,
|
|
value: @escaping (Database) throws -> Output)
|
|
-> DatabasePublishers.Read<Output>
|
|
{
|
|
Deferred {
|
|
Future { fulfill in
|
|
self.asyncRead { dbResult in
|
|
fulfill(dbResult.flatMap { db in Result { try value(db) } })
|
|
}
|
|
}
|
|
}
|
|
.receiveValues(on: scheduler)
|
|
.eraseToReadPublisher()
|
|
}
|
|
}
|
|
|
|
@available(iOS 13, macOS 10.15, tvOS 13, watchOS 6, *)
|
|
extension DatabasePublishers {
|
|
/// A publisher that reads from the database.
|
|
///
|
|
/// `Read` publishes exactly one element, or an error.
|
|
///
|
|
/// You build such a publisher from ``DatabaseReader``.
|
|
public struct Read<Output>: Publisher {
|
|
public typealias Output = Output
|
|
public typealias Failure = Error
|
|
|
|
fileprivate let upstream: AnyPublisher<Output, Error>
|
|
|
|
public func receive<S>(subscriber: S) where S: Subscriber, Self.Failure == S.Failure, Self.Output == S.Input {
|
|
upstream.receive(subscriber: subscriber)
|
|
}
|
|
}
|
|
}
|
|
|
|
@available(iOS 13, macOS 10.15, tvOS 13, watchOS 6, *)
|
|
extension Publisher where Failure == Error {
|
|
fileprivate func eraseToReadPublisher() -> DatabasePublishers.Read<Output> {
|
|
.init(upstream: eraseToAnyPublisher())
|
|
}
|
|
}
|
|
#endif
|
|
|
|
extension DatabaseReader {
|
|
// MARK: - Value Observation Support
|
|
|
|
/// Adding an observation in a read-only database emits only the
|
|
/// initial value.
|
|
func _addReadOnly<Reducer: ValueReducer>(
|
|
observation: ValueObservation<Reducer>,
|
|
scheduling scheduler: some ValueObservationScheduler,
|
|
onChange: @escaping (Reducer.Value) -> Void)
|
|
-> AnyDatabaseCancellable
|
|
{
|
|
if scheduler.immediateInitialValue() {
|
|
do {
|
|
// Perform a reentrant read, in case the observation would be
|
|
// started from a database access.
|
|
let value = try unsafeReentrantRead { db in
|
|
try db.isolated(readOnly: true) {
|
|
try observation.fetchInitialValue(db)
|
|
}
|
|
}
|
|
onChange(value)
|
|
} catch {
|
|
observation.events.didFail?(error)
|
|
}
|
|
return AnyDatabaseCancellable(cancel: { /* nothing to cancel */ })
|
|
} else {
|
|
var isCancelled = false
|
|
asyncRead { dbResult in
|
|
guard !isCancelled else { return }
|
|
|
|
let result = dbResult.flatMap { db in
|
|
Result { try observation.fetchInitialValue(db) }
|
|
}
|
|
|
|
scheduler.schedule {
|
|
guard !isCancelled else { return }
|
|
do {
|
|
try onChange(result.get())
|
|
} catch {
|
|
observation.events.didFail?(error)
|
|
}
|
|
}
|
|
}
|
|
return AnyDatabaseCancellable(cancel: { isCancelled = true })
|
|
}
|
|
}
|
|
}
|
|
|
|
/// A type-erased database reader.
|
|
///
|
|
/// An instance of `AnyDatabaseReader` forwards its operations to an underlying
|
|
/// base database reader.
|
|
public final class AnyDatabaseReader {
|
|
private let base: any DatabaseReader
|
|
|
|
/// Creates a new database reader that wraps and forwards operations
|
|
/// to `base`.
|
|
public init(_ base: some DatabaseReader) {
|
|
self.base = base
|
|
}
|
|
}
|
|
|
|
extension AnyDatabaseReader: DatabaseReader {
|
|
public var configuration: Configuration {
|
|
base.configuration
|
|
}
|
|
|
|
public var path: String {
|
|
base.path
|
|
}
|
|
|
|
public func close() throws {
|
|
try base.close()
|
|
}
|
|
|
|
public func interrupt() {
|
|
base.interrupt()
|
|
}
|
|
|
|
@_disfavoredOverload // SR-15150 Async overloading in protocol implementation fails
|
|
public func read<T>(_ value: (Database) throws -> T) throws -> T {
|
|
try base.read(value)
|
|
}
|
|
|
|
public func asyncRead(_ value: @escaping (Result<Database, Error>) -> Void) {
|
|
base.asyncRead(value)
|
|
}
|
|
|
|
@_disfavoredOverload // SR-15150 Async overloading in protocol implementation fails
|
|
public func unsafeRead<T>(_ value: (Database) throws -> T) throws -> T {
|
|
try base.unsafeRead(value)
|
|
}
|
|
|
|
public func asyncUnsafeRead(_ value: @escaping (Result<Database, Error>) -> Void) {
|
|
base.asyncUnsafeRead(value)
|
|
}
|
|
|
|
public func unsafeReentrantRead<T>(_ value: (Database) throws -> T) throws -> T {
|
|
try base.unsafeReentrantRead(value)
|
|
}
|
|
|
|
public func _add<Reducer: ValueReducer>(
|
|
observation: ValueObservation<Reducer>,
|
|
scheduling scheduler: some ValueObservationScheduler,
|
|
onChange: @escaping (Reducer.Value) -> Void)
|
|
-> AnyDatabaseCancellable
|
|
{
|
|
base._add(
|
|
observation: observation,
|
|
scheduling: scheduler,
|
|
onChange: onChange)
|
|
}
|
|
}
|
|
|
|
/// A type that sees an unchanging database content.
|
|
///
|
|
/// Do not declare new conformances to `DatabaseSnapshotReader`. Only the
|
|
/// built-in conforming types are valid.
|
|
///
|
|
/// The protocol comes with the same features and guarantees as
|
|
/// ``DatabaseReader``. On top of them, a `DatabaseSnapshotReader` always sees
|
|
/// the same state of the database.
|
|
///
|
|
/// ## Topics
|
|
///
|
|
/// ### Reading from the Database
|
|
///
|
|
/// - ``reentrantRead(_:)``
|
|
public protocol DatabaseSnapshotReader: DatabaseReader { }
|
|
|
|
extension DatabaseSnapshotReader {
|
|
/// Executes database operations, and returns their result after they have
|
|
/// finished executing.
|
|
///
|
|
/// This method can be called from other database access methods. If called
|
|
/// from the dispatch queue of a current database access, the `Database`
|
|
/// argument to `value` is the same as the current database access.
|
|
///
|
|
/// For example:
|
|
///
|
|
/// ```swift
|
|
/// let count = try snapshot.reentrantRead { db in
|
|
/// try Player.fetchCount(db)
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// The ``Database`` argument to `value` is valid only during the execution
|
|
/// of the closure. Do not store or return the database connection for
|
|
/// later use.
|
|
///
|
|
/// - parameter value: A closure which accesses the database.
|
|
/// - throws: The error thrown by `value`, or any ``DatabaseError`` that
|
|
/// would happen while establishing the database access.
|
|
public func reentrantRead<T>(_ value: (Database) throws -> T) throws -> T {
|
|
// Reentrant reads are safe in a snapshot
|
|
try unsafeReentrantRead(value)
|
|
}
|
|
|
|
// There is no such thing as an unsafe access to a snapshot.
|
|
public func unsafeRead<T>(_ value: (Database) throws -> T) throws -> T {
|
|
try read(value)
|
|
}
|
|
|
|
// There is no such thing as an unsafe access to a snapshot.
|
|
public func asyncUnsafeRead(_ value: @escaping (Result<Database, Error>) -> Void) {
|
|
asyncRead(value)
|
|
}
|
|
}
|