455 lines
14 KiB
Swift
455 lines
14 KiB
Swift
//
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// DatabaseLookupTable.swift
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// RSDatabase
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//
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// Created by Brent Simmons on 8/5/17.
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// Copyright © 2017 Ranchero Software, LLC. All rights reserved.
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//
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import Foundation
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// Implement a lookup table for a many-to-many relationship.
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// Example: CREATE TABLE if not EXISTS authorLookup (authorID TEXT NOT NULL, articleID TEXT NOT NULL, PRIMARY KEY(authorID, articleID));
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// articleID is objectID; authorID is relatedObjectID.
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public final class DatabaseLookupTable {
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private let name: String
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private let objectIDKey: String
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private let relatedObjectIDKey: String
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private let relationshipName: String
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private let relatedTable: DatabaseRelatedObjectsTable
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private let cache: DatabaseLookupTableCache
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private var objectIDsWithNoRelatedObjects = Set<String>()
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public init(name: String, objectIDKey: String, relatedObjectIDKey: String, relatedTable: DatabaseRelatedObjectsTable, relationshipName: String) {
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self.name = name
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self.objectIDKey = objectIDKey
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self.relatedObjectIDKey = relatedObjectIDKey
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self.relatedTable = relatedTable
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self.relationshipName = relationshipName
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self.cache = DatabaseLookupTableCache(relationshipName)
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}
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public func fetchRelatedObjects(for objectIDs: Set<String>, in database: FMDatabase) -> RelatedObjectsMap? {
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let objectIDsThatMayHaveRelatedObjects = objectIDs.subtracting(objectIDsWithNoRelatedObjects)
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if objectIDsThatMayHaveRelatedObjects.isEmpty {
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return nil
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}
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guard let lookupTable = fetchLookupTable(objectIDsThatMayHaveRelatedObjects, database) else {
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objectIDsWithNoRelatedObjects.formUnion(objectIDsThatMayHaveRelatedObjects)
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return nil
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}
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if let relatedObjects = fetchRelatedObjectsReferencedByLookupTable(LookupTable, database) {
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let relatedObjectsDictionary = relatedObjectsDictionary(lookupTable, relatedObjects)
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let objectIDsWithNoFetchedRelatedObjects = objectIDsThatMayHaveRelatedObjects.subtracting(Set(relatedObjectsDictionary.keys))
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objectIDsWithNoRelatedObjects.formUnion(objectIDsWithNoFetchedRelatedObjects)
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return relatedObjectsDictionary
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}
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return nil
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}
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public func attachRelatedObjects(to objects: [DatabaseObject], in database: FMDatabase) {
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let objectsThatMayHaveRelatedObjects = cache.objectsThatMayHaveRelatedObjects(objects)
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if objectsThatMayHaveRelatedObjects.isEmpty {
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return
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}
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attachRelatedObjectsUsingCache(objectsThatMayHaveRelatedObjects, database)
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let objectsNeedingFetching = objectsThatMayHaveRelatedObjects.filter { (object) -> Bool in
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return object.relatedObjectsWithName(self.relationshipName) == nil
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}
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if objectsNeedingFetching.isEmpty {
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return
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}
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if let lookupTable = fetchLookupTable(objectsNeedingFetching.databaseIDs(), database) {
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attachRelatedObjectsUsingLookupTable(objectsNeedingFetching, lookupTable, database)
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}
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cache.update(with: objectsNeedingFetching)
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}
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public func saveRelatedObjects(for objects: [DatabaseObject], in database: FMDatabase) {
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var objectsWithNoRelationships = [DatabaseObject]()
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var objectsWithRelationships = [DatabaseObject]()
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for object in objects {
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if let relatedObjects = object.relatedObjectsWithName(relationshipName), !relatedObjects.isEmpty {
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objectsWithRelationships += [object]
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}
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else {
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objectsWithNoRelationships += [object]
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}
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}
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removeRelationships(for: objectsWithNoRelationships, database)
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updateRelationships(for: objectsWithRelationships, database)
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cache.update(with: objects)
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}
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}
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// MARK: - Private
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private extension DatabaseLookupTable {
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// MARK: Removing
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func removeRelationships(for objects: [DatabaseObject], _ database: FMDatabase) {
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let objectIDs = objects.databaseIDs()
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let objectIDsToRemove = objectIDs.subtracting(cache.objectIDsWithNoRelationship)
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if objectIDsToRemove.isEmpty {
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return
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}
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database.rs_deleteRowsWhereKey(objectIDKey, inValues: Array(objectIDsToRemove), tableName: name)
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}
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func deleteLookups(for objectID: String, _ relatedObjectIDs: Set<String>, _ database: FMDatabase) {
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guard !relatedObjectIDs.isEmpty else {
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assertionFailure("deleteLookups: expected non-empty relatedObjectIDs")
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return
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}
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// delete from authorLookup where articleID=? and authorID in (?,?,?)
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let placeholders = NSString.rs_SQLValueList(withPlaceholders: UInt(relatedObjectIDs.count))!
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let sql = "delete from \(name) where \(objectIDKey)=? and \(relatedObjectIDKey) in \(placeholders)"
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let parameters: [Any] = [objectID] + Array(relatedObjectIDs)
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let _ = database.executeUpdate(sql, withArgumentsIn: parameters)
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}
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// MARK: Saving/Updating
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func updateRelationships(for objects: [DatabaseObject], _ database: FMDatabase) {
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let objectsNeedingUpdate = objects.filter { !relatedObjectIDsMatchesCache($0) }
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if objectsNeedingUpdate.isEmpty {
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return
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}
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if let lookupTable = fetchLookupTable(objectsNeedingUpdate.databaseIDs(), database) {
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for object in objectsNeedingUpdate {
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syncRelatedObjectsAndLookupTable(object, lookupTable, database)
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}
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}
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// Save the actual related objects.
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let relatedObjectsToSave = uniqueArrayOfRelatedObjects(with: objectsNeedingUpdate)
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if relatedObjectsToSave.isEmpty {
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assertionFailure("updateRelationships: expected relatedObjectsToSave would not be empty. This should be unreachable.")
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return
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}
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relatedTable.save(relatedObjectsToSave, in: database)
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}
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func uniqueArrayOfRelatedObjects(with objects: [DatabaseObject]) -> [DatabaseObject] {
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// Can’t create a Set, because we can’t make a Set<DatabaseObject>, because protocol-conforming objects can’t be made Hashable or even Equatable.
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// We still want the array to include only one copy of each object, but we have to do it the slow way. Instruments will tell us if this is a performance problem.
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var relatedObjectsUniqueArray = [DatabaseObject]()
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for object in objects {
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guard let relatedObjects = object.relatedObjectsWithName(relationshipName) else {
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assertionFailure("uniqueArrayOfRelatedObjects: expected every object to have related objects.")
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continue
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}
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for relatedObject in relatedObjects {
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if !relatedObjectsUniqueArray.includesObjectWithDatabaseID(relatedObject.databaseID) {
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relatedObjectsUniqueArray += [relatedObject]
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}
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}
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}
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return relatedObjectsUniqueArray
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}
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func relatedObjectIDsMatchesCache(_ object: DatabaseObject) -> Bool {
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let relatedObjects = object.relatedObjectsWithName(relationshipName) ?? [DatabaseObject]()
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let cachedRelationshipIDs = cache[object.databaseID] ?? Set<String>()
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return relatedObjects.databaseIDs() == cachedRelationshipIDs
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}
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func syncRelatedObjectsAndLookupTable(_ object: DatabaseObject, _ lookupTable: LookupTable, _ database: FMDatabase) {
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guard let relatedObjects = object.relatedObjectsWithName(relationshipName) else {
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assertionFailure("syncRelatedObjectsAndLookupTable should be called only on objects with related objects.")
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return
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}
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let relatedObjectIDs = relatedObjects.databaseIDs()
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let lookupTableRelatedObjectIDs = lookupTable[object.databaseID] ?? Set<String>()
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let relatedObjectIDsToDelete = lookupTableRelatedObjectIDs.subtracting(relatedObjectIDs)
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if !relatedObjectIDsToDelete.isEmpty {
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deleteLookups(for: object.databaseID, relatedObjectIDsToDelete, database)
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}
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let relatedObjectIDsToSave = relatedObjectIDs.subtracting(lookupTableRelatedObjectIDs)
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if !relatedObjectIDsToSave.isEmpty {
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saveLookups(for: object.databaseID, relatedObjectIDsToSave, database)
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}
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}
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func saveLookups(for objectID: String, _ relatedObjectIDs: Set<String>, _ database: FMDatabase) {
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for relatedObjectID in relatedObjectIDs {
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let d: [NSObject: Any] = [(objectIDKey as NSString): objectID, (relatedObjectIDKey as NSString): relatedObjectID]
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let _ = database.rs_insertRow(with: d, insertType: .orIgnore, tableName: name)
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}
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}
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// MARK: Attaching
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func attachRelatedObjectsUsingCache(_ objects: [DatabaseObject], _ database: FMDatabase) {
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let lookupTable = cache.lookupTableForObjectIDs(objects.databaseIDs())
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attachRelatedObjectsUsingLookupTable(objects, lookupTable, database)
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}
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func fetchRelatedObjectsReferencedByLookupTable(_ lookupTable: LookupTable, _ database: FMDatabase) -> [DatabaseObject]? {
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let relatedObjectIDs = lookupTable.relatedObjectIDs()
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if (relatedObjectIDs.isEmpty) {
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return nil
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}
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return fetchRelatedObjectsWithIDs(relatedObjectIDs)
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}
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func attachRelatedObjectsUsingLookupTable(_ objects: [DatabaseObject], _ lookupTable: LookupTable, _ database: FMDatabase) {
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let relatedObjectIDs = lookupTable.relatedObjectIDs()
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if (relatedObjectIDs.isEmpty) {
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return
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}
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guard let relatedObjects = fetchRelatedObjectsWithIDs(relatedObjectIDs, database) else {
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return
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}
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let relatedObjectsDictionary = relatedObjects.dictionary()
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for object in objects {
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attachRelatedObjectsToObjectUsingLookupTable(object, relatedObjectsDictionary, lookupTable)
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}
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}
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func attachRelatedObjectsToObjectUsingLookupTable(_ object: DatabaseObject, _ relatedObjectsDictionary: [String: DatabaseObject], _ lookupTable: LookupTable) {
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let identifier = object.databaseID
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guard let relatedObjectIDs = lookupTable[identifier], !relatedObjectIDs.isEmpty else {
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return
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}
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let relatedObjects = relatedObjectIDs.flatMap { relatedObjectsDictionary[$0] }
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if !relatedObjects.isEmpty {
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object.setRelatedObjects(relatedObjects, name: relationshipName)
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}
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}
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// MARK: Fetching
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func fetchRelatedObjectsWithIDs(_ relatedObjectIDs: Set<String>, _ database: FMDatabase) -> [DatabaseObject]? {
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let relatedObjects = relatedTable.fetchObjectsWithIDs(relatedObjectIDs, in: database)
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if relatedObjects.isEmpty {
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return nil
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}
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return relatedObjects
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}
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func fetchLookupTable(_ objectIDs: Set<String>, _ database: FMDatabase) -> LookupTable? {
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guard let lookupValues = fetchLookupValues(objectIDs, database) else {
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return nil
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}
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return LookupTable(lookupValues: lookupValues)
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}
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func fetchLookupValues(_ objectIDs: Set<String>, _ database: FMDatabase) -> Set<LookupValue>? {
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guard !objectIDs.isEmpty, let resultSet = database.rs_selectRowsWhereKey(objectIDKey, inValues: Array(objectIDs), tableName: name) else {
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return nil
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}
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return lookupValuesWithResultSet(resultSet)
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}
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func lookupValuesWithResultSet(_ resultSet: FMResultSet) -> Set<LookupValue> {
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return resultSet.mapToSet(lookupValueWithRow)
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}
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func lookupValueWithRow(_ row: FMResultSet) -> LookupValue? {
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guard let objectID = row.string(forColumn: objectIDKey) else {
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return nil
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}
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guard let relatedObjectID = row.string(forColumn: relatedObjectIDKey) else {
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return nil
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}
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return LookupValue(objectID: objectID, relatedObjectID: relatedObjectID)
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}
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func relatedObjectsDictionary(_ lookupTable: LookupTable, relatedObjects: [DatabaseObject]) -> RelatedObjectsDictionary? {
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var relatedObjectsDictionary = RelatedObjectsDictionary()
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let d = relatedObjects.dictionary()
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return relatedObjectsDictionary.isEmpty ? nil : relatedObjectsDictionary
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}
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}
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// MARK: -
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private struct LookupTable {
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private let dictionary: [String: Set<String>] // objectID: Set<relatedObjectID>
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init(dictionary: [String: Set<String>]) {
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self.dictionary = dictionary
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}
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init(lookupValues: Set<LookupValue>) {
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var d = [String: Set<String>]()
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for lookupValue in lookupValues {
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let objectID = lookupValue.objectID
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let relatedObjectID: String = lookupValue.relatedObjectID
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if d[objectID] == nil {
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d[objectID] = Set([relatedObjectID])
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}
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else {
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d[objectID]!.insert(relatedObjectID)
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}
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}
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self.init(dictionary: d)
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}
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func objectIDs() -> Set<String> {
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return Set(dictionary.keys)
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}
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func relatedObjectIDs() -> Set<String> {
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var ids = Set<String>()
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for (_, relatedObjectIDs) in dictionary {
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ids.formUnion(relatedObjectIDs)
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}
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return ids
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}
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subscript(_ objectID: String) -> Set<String>? {
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get {
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return dictionary[objectID]
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}
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}
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}
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private struct LookupValue: Hashable {
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let objectID: String
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let relatedObjectID: String
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let hashValue: Int
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init(objectID: String, relatedObjectID: String) {
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self.objectID = objectID
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self.relatedObjectID = relatedObjectID
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self.hashValue = (objectID + relatedObjectID).hashValue
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}
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static public func ==(lhs: LookupValue, rhs: LookupValue) -> Bool {
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return lhs.objectID == rhs.objectID && lhs.relatedObjectID == rhs.relatedObjectID
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}
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}
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private final class DatabaseLookupTableCache {
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var objectIDsWithNoRelationship = Set<String>()
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private let relationshipName: String
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private var cachedLookups = [String: Set<String>]() // objectID: Set<relatedObjectID>
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init(_ relationshipName: String) {
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self.relationshipName = relationshipName
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}
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func update(with objects: [DatabaseObject]) {
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var idsWithRelationships = Set<String>()
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var idsWithNoRelationships = Set<String>()
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for object in objects {
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let objectID = object.databaseID
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if let relatedObjects = object.relatedObjectsWithName(relationshipName), !relatedObjects.isEmpty {
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idsWithRelationships.insert(objectID)
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self[objectID] = relatedObjects.databaseIDs()
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}
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else {
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idsWithNoRelationships.insert(objectID)
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self[objectID] = nil
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}
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}
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objectIDsWithNoRelationship.subtract(idsWithRelationships)
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objectIDsWithNoRelationship.formUnion(idsWithNoRelationships)
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}
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subscript(_ objectID: String) -> Set<String>? {
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get {
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return cachedLookups[objectID]
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}
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set {
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cachedLookups[objectID] = newValue
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}
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}
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func objectIDsThatMayHaveRelatedObjects(_ objectIDs: Set<String>) -> Set<String> {
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// Filter out objects that are known to have no related objects
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return Set(objectIDs.filter{ !objectIDsWithNoRelationship.contains($0) })
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}
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// func objectsThatMayHaveRelatedObjects(_ objects: [DatabaseObject]) -> [DatabaseObject] {
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//
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// // Filter out objects that are known to have no related objects
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// return objects.filter{ !objectIDsWithNoRelationship.contains($0.databaseID) }
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// }
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func lookupTableForObjectIDs(_ objectIDs: Set<String>) -> LookupTable {
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var d = [String: Set<String>]()
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for objectID in objectIDs {
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if let relatedObjectIDs = self[objectID] {
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d[objectID] = relatedObjectIDs
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}
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}
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return LookupTable(dictionary: d)
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}
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}
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