zeus
472 lines
17 KiB
Swift
472 lines
17 KiB
Swift
/// An observable region of the database.
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///
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/// A `DatabaseRegion` is the union of any number of "table regions", which can
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/// cover a full table, or the combination of columns and rows identified by
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/// their rowids:
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///
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/// |Table1 | |Table2 | |Table3 | |Table4 | |Table5 |
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/// |-------| |-------| |-------| |-------| |-------|
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/// |x|x|x|x| |x| | | | |x|x|x|x| |x|x| |x| | | | | |
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/// |x|x|x|x| |x| | | | | | | | | | | | | | | |x| | |
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/// |x|x|x|x| |x| | | | | | | | | |x|x| |x| | | | | |
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/// |x|x|x|x| |x| | | | | | | | | | | | | | | | | | |
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///
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/// It is dedicated to help ``TransactionObserver`` types detect impactful
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/// database changes.
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///
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/// You get `DatabaseRegion` instances from a ``DatabaseRegionConvertible``
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/// value, a prepared ``Statement``, or from the initializers described below.
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///
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/// ## Topics
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///
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/// ### Creating Regions
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///
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/// - ``fullDatabase-3ir3p``
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/// - ``init()``
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///
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/// ### Instance Properties
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///
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/// - ``isEmpty``
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/// - ``isFullDatabase``
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///
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/// ### Combining Regions
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///
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/// - ``formUnion(_:)``
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/// - ``union(_:)``
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///
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/// ### Detecting Database Changes
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///
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/// Use those methods from ``TransactionObserver`` methods.
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///
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/// - ``isModified(byEventsOfKind:)``
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/// - ``isModified(by:)``
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public struct DatabaseRegion: Sendable {
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private let tableRegions: [CaseInsensitiveIdentifier: TableRegion]?
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private init(tableRegions: [CaseInsensitiveIdentifier: TableRegion]?) {
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self.tableRegions = tableRegions
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}
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/// Returns whether the region is empty.
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public var isEmpty: Bool {
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guard let tableRegions else {
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// full database
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return false
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}
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return tableRegions.isEmpty
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}
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/// Returns whether the region covers the full database.
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public var isFullDatabase: Bool {
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tableRegions == nil
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}
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/// The region that covers the full database.
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public static let fullDatabase = DatabaseRegion(tableRegions: nil)
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/// The empty database region.
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public init() {
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self.init(tableRegions: [:])
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}
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/// Creates a region that spans all rows and columns of a database table.
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///
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/// - parameter table: A table name.
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init(table: String) {
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let table = CaseInsensitiveIdentifier(rawValue: table)
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self.init(tableRegions: [table: TableRegion(columns: nil, rowIds: nil)])
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}
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/// Full columns in a table: (some columns in a table) × (all rows)
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init(table: String, columns: Set<String>) {
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let table = CaseInsensitiveIdentifier(rawValue: table)
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let columns = Set(columns.map(CaseInsensitiveIdentifier.init))
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self.init(tableRegions: [table: TableRegion(columns: columns, rowIds: nil)])
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}
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/// Full rows in a table: (all columns in a table) × (some rows)
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init(table: String, rowIds: Set<Int64>) {
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let table = CaseInsensitiveIdentifier(rawValue: table)
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self.init(tableRegions: [table: TableRegion(columns: nil, rowIds: rowIds)])
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}
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/// Returns the intersection of this region and the given one.
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///
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/// This method is not public because there is no known public use case for
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/// this intersection. It is currently only used as support for
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/// the isModified(byEventsOfKind:) method.
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func intersection(_ other: DatabaseRegion) -> DatabaseRegion {
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guard let tableRegions else { return other }
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guard let otherTableRegions = other.tableRegions else { return self }
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var tableRegionsIntersection: [CaseInsensitiveIdentifier: TableRegion] = [:]
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for (table, tableRegion) in tableRegions {
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guard let otherTableRegion = otherTableRegions
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.first(where: { (otherTable, _) in otherTable == table })?
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.value else { continue }
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let tableRegionIntersection = tableRegion.intersection(otherTableRegion)
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guard !tableRegionIntersection.isEmpty else { continue }
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tableRegionsIntersection[table] = tableRegionIntersection
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}
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return DatabaseRegion(tableRegions: tableRegionsIntersection)
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}
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/// Only keeps those rowIds in the given table
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func tableIntersection(_ table: String, rowIds: Set<Int64>) -> DatabaseRegion {
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guard var tableRegions else {
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return DatabaseRegion(table: table, rowIds: rowIds)
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}
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let table = CaseInsensitiveIdentifier(rawValue: table)
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guard let tableRegion = tableRegions[table] else {
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return self
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}
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let intersection = tableRegion.intersection(TableRegion(columns: nil, rowIds: rowIds))
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if intersection.isEmpty {
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tableRegions.removeValue(forKey: table)
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} else {
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tableRegions[table] = intersection
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}
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return DatabaseRegion(tableRegions: tableRegions)
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}
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/// Returns the union of this region and the given one.
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public func union(_ other: DatabaseRegion) -> DatabaseRegion {
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guard let tableRegions else { return .fullDatabase }
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guard let otherTableRegions = other.tableRegions else { return .fullDatabase }
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var tableRegionsUnion: [CaseInsensitiveIdentifier: TableRegion] = [:]
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let tableNames = Set(tableRegions.keys).union(Set(otherTableRegions.keys))
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for table in tableNames {
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let tableRegion = tableRegions[table]
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let otherTableRegion = otherTableRegions[table]
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let tableRegionUnion: TableRegion
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switch (tableRegion, otherTableRegion) {
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case (nil, nil):
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preconditionFailure()
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case let (nil, tableRegion?), let (tableRegion?, nil):
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tableRegionUnion = tableRegion
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case let (tableRegion?, otherTableRegion?):
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tableRegionUnion = tableRegion.union(otherTableRegion)
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}
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tableRegionsUnion[table] = tableRegionUnion
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}
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return DatabaseRegion(tableRegions: tableRegionsUnion)
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}
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/// Inserts the given region into this region
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public mutating func formUnion(_ other: DatabaseRegion) {
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self = union(other)
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}
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/// Returns a region suitable for database observation
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func observableRegion(_ db: Database) throws -> DatabaseRegion {
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// SQLite does not expose schema changes to the
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// TransactionObserver protocol. By removing internal SQLite tables from
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// the observed region, we optimize database observation.
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//
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// And by canonicalizing table names, we remove views, and help the
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// `isModified` methods. (TODO: is this comment still accurate?
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// Isn't it about providing TransactionObserver.observes() with
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// real tables names, instead?)
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try ignoringInternalSQLiteTables().canonicalTables(db)
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}
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/// Returns a region only made of actual tables with their canonical names.
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///
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/// This method removes views.
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func canonicalTables(_ db: Database) throws -> DatabaseRegion {
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guard let tableRegions else { return .fullDatabase }
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var region = DatabaseRegion()
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for (table, tableRegion) in tableRegions {
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if let canonicalTableName = try db.canonicalTableName(table.rawValue) {
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let table = CaseInsensitiveIdentifier(rawValue: canonicalTableName)
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region.formUnion(DatabaseRegion(tableRegions: [table: tableRegion]))
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}
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}
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return region
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}
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/// Returns a region which doesn't contain any SQLite internal table.
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private func ignoringInternalSQLiteTables() -> DatabaseRegion {
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guard let tableRegions else { return .fullDatabase }
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let filteredRegions = tableRegions.filter {
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!Database.isSQLiteInternalTable($0.key.rawValue)
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}
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return DatabaseRegion(tableRegions: filteredRegions)
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}
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}
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extension DatabaseRegion {
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// MARK: - Database Events
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/// Returns whether the content in the region would be impacted if the
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/// database were modified by an event of this kind.
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public func isModified(byEventsOfKind eventKind: DatabaseEventKind) -> Bool {
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intersection(eventKind.modifiedRegion).isEmpty == false
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}
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/// Returns whether the content in the region is impacted by this event.
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///
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/// - precondition: event has been filtered by the same region
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/// in the TransactionObserver.observes(eventsOfKind:) method, by calling
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/// region.isModified(byEventsOfKind:)
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public func isModified(by event: DatabaseEvent) -> Bool {
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guard let tableRegions else {
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// Full database: all changes are impactful
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return true
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}
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guard let tableRegion = tableRegions[CaseInsensitiveIdentifier(rawValue: event.tableName)] else {
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// FTS4 (and maybe other virtual tables) perform unadvertised
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// changes. For example, an "INSERT INTO document ..." statement
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// advertises an insertion in the `document` table, but the
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// actual change events happen in the `document_content` shadow
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// table. When such a non-advertised event happens, assume that
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// the region is modified.
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// See https://github.com/groue/GRDB.swift/issues/620
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return true
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}
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return tableRegion.contains(rowID: event.rowID)
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}
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/// Returns an array of all event kinds that can impact this region.
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///
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/// - precondition: the region is canonical.
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func impactfulEventKinds(_ db: Database) throws -> [DatabaseEventKind] {
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if let tableRegions {
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return try tableRegions.flatMap { (table, tableRegion) -> [DatabaseEventKind] in
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let tableName = table.rawValue // canonical table name
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let columnNames: Set<String>
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if let columns = tableRegion.columns {
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columnNames = Set(columns.map(\.rawValue))
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} else {
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columnNames = try Set(db.columns(in: tableName).map(\.name))
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}
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return [
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DatabaseEventKind.delete(tableName: tableName),
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DatabaseEventKind.insert(tableName: tableName),
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DatabaseEventKind.update(tableName: tableName, columnNames: columnNames),
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]
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}
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} else {
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// full database
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return try db.schemaIdentifiers().flatMap { schemaIdentifier in
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let schema = try db.schema(schemaIdentifier)
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return try schema.objects
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.filter { $0.type == .table }
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.flatMap { table in
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let columnNames = try Set(db.columns(in: table.name).map(\.name))
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return [
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DatabaseEventKind.delete(tableName: table.name),
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DatabaseEventKind.insert(tableName: table.name),
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DatabaseEventKind.update(tableName: table.name, columnNames: columnNames),
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]
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}
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}
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}
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}
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}
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extension DatabaseRegion: Equatable {
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public static func == (lhs: DatabaseRegion, rhs: DatabaseRegion) -> Bool {
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switch (lhs.tableRegions, rhs.tableRegions) {
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case (nil, nil):
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return true
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case let (ltableRegions?, rtableRegions?):
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let ltableNames = Set(ltableRegions.keys)
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let rtableNames = Set(rtableRegions.keys)
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guard ltableNames == rtableNames else {
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return false
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}
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for tableName in ltableNames where ltableRegions[tableName]! != rtableRegions[tableName]! {
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return false
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}
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return true
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default:
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return false
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}
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}
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}
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extension DatabaseRegion: CustomStringConvertible {
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public var description: String {
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guard let tableRegions else {
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return "full database"
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}
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if tableRegions.isEmpty {
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return "empty"
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}
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return tableRegions
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.sorted(by: { (l, r) in l.key.rawValue < r.key.rawValue })
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.map { (table, tableRegion) in
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var desc = table.rawValue
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if let columns = tableRegion.columns {
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desc += "(" + columns.map(\.rawValue).sorted().joined(separator: ",") + ")"
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} else {
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desc += "(*)"
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}
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if let rowIds = tableRegion.rowIds {
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desc += "[" + rowIds.sorted().map { "\($0)" }.joined(separator: ",") + "]"
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}
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return desc
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}
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.joined(separator: ",")
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}
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}
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private struct TableRegion: Equatable {
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var columns: Set<CaseInsensitiveIdentifier>? // nil means "all columns"
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var rowIds: Set<Int64>? // nil means "all rowids"
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var isEmpty: Bool {
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if let columns, columns.isEmpty { return true }
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if let rowIds, rowIds.isEmpty { return true }
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return false
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}
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func intersection(_ other: TableRegion) -> TableRegion {
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let columnsIntersection: Set<CaseInsensitiveIdentifier>?
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switch (self.columns, other.columns) {
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case let (nil, columns), let (columns, nil):
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columnsIntersection = columns
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case let (columns?, other?):
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columnsIntersection = columns.intersection(other)
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}
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let rowIdsIntersection: Set<Int64>?
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switch (self.rowIds, other.rowIds) {
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case let (nil, rowIds), let (rowIds, nil):
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rowIdsIntersection = rowIds
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case let (rowIds?, other?):
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rowIdsIntersection = rowIds.intersection(other)
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}
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return TableRegion(columns: columnsIntersection, rowIds: rowIdsIntersection)
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}
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func union(_ other: TableRegion) -> TableRegion {
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let columnsUnion: Set<CaseInsensitiveIdentifier>?
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switch (self.columns, other.columns) {
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case (nil, _), (_, nil):
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columnsUnion = nil
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case let (columns?, other?):
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columnsUnion = columns.union(other)
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}
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let rowIdsUnion: Set<Int64>?
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switch (self.rowIds, other.rowIds) {
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case (nil, _), (_, nil):
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rowIdsUnion = nil
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case let (rowIds?, other?):
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rowIdsUnion = rowIds.union(other)
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}
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return TableRegion(columns: columnsUnion, rowIds: rowIdsUnion)
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}
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func contains(rowID: Int64) -> Bool {
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guard let rowIds else {
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return true
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}
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return rowIds.contains(rowID)
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}
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}
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// MARK: - DatabaseRegionConvertible
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/// A type that operates on a specific ``DatabaseRegion``.
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///
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/// A `DatabaseRegionConvertible` instance feeds database observation tools such
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/// as ``DatabaseRegionObservation`` and ``ValueObservation``:
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///
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/// ```swift
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/// // An observation triggered by all changes to the database
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/// DatabaseRegionObservation(tracking: .fullDatabase)
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///
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/// // An observation triggered by all changes to the 'player' table
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/// DatabaseRegionObservation(tracking: Table("player"))
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///
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/// // An observation triggered by all changes to the row
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/// // with rowid 1 in the 'player' table
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/// DatabaseRegionObservation(tracking: Player.filter(id: 1))
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///
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/// // An observation triggered by all changes to the 'score' column
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/// // of the 'player' table
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/// DatabaseRegionObservation(tracking: SQLRequest("SELECT score FROM player"))
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/// ```
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///
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/// Specifying a region from a ``FetchRequest`` does not execute the request.
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/// In the above example, `Player.filter(id: 1)` and `SELECT score FROM player`
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/// are only compiled by SQLite, so that GRDB can understand the tables, rows,
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/// and columns that constitute the database region.
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///
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/// ## Topics
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///
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/// ### Creating a DatabaseRegion
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///
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/// - ``fullDatabase``
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/// - ``databaseRegion(_:)``
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///
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/// ### Supporting Types
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///
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/// - ``AnyDatabaseRegionConvertible``
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public protocol DatabaseRegionConvertible {
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/// Returns a database region.
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///
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/// - parameter db: A database connection.
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func databaseRegion(_ db: Database) throws -> DatabaseRegion
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}
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extension DatabaseRegionConvertible where Self == DatabaseRegion {
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/// The region that covers the full database: all columns and all rows
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/// from all tables.
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public static var fullDatabase: Self { DatabaseRegion.fullDatabase }
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}
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extension DatabaseRegion: DatabaseRegionConvertible {
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public func databaseRegion(_ db: Database) throws -> DatabaseRegion {
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self
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}
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}
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/// A type-erased DatabaseRegionConvertible
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public struct AnyDatabaseRegionConvertible: DatabaseRegionConvertible {
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let _region: (Database) throws -> DatabaseRegion
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public init(_ region: @escaping (Database) throws -> DatabaseRegion) {
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_region = region
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}
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public init(_ region: some DatabaseRegionConvertible) {
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_region = region.databaseRegion
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}
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public func databaseRegion(_ db: Database) throws -> DatabaseRegion {
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try _region(db)
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}
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}
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// MARK: - Utils
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extension DatabaseRegion {
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static func union(_ regions: DatabaseRegion...) -> DatabaseRegion {
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regions.reduce(into: DatabaseRegion()) { union, region in
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union.formUnion(region)
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}
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}
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static func union(_ regions: [any DatabaseRegionConvertible]) -> (Database) throws -> DatabaseRegion {
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return { db in
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try regions.reduce(into: DatabaseRegion()) { union, region in
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try union.formUnion(region.databaseRegion(db))
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}
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}
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}
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}
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