我正在为我的Core Data模型设计一个数据管理器,我想创建一个通用函数来获取类的亲戚。
我创建了一个允许为每种数据类型构建管理器的协议。在这个协议中,我已经定义了两个相关的类型T和K以及几个简单的函数。现在我坚持使用类亲戚提取方法 - 我需要以某种方式表明T有K亲戚。我试图通过相互属性创建一些指示这种关系的协议是徒劳的,所以这两个类都可以符合这个协议。任何想法,甚至可能吗?
import Foundation
import CoreData
protocol DataManager {
associatedtype T: NSManagedObject, NSFetchRequestResult
associatedtype K: NSManagedObject, NSFetchRequestResult // Relative
static var sharedInstance: Self { get }
static func getAll(sorted: [NSSortDescriptor]?, context: NSManagedObjectContext) -> [T]?
static func insert(item: T)
static func update(item: T)
static func clean()
static func deleteById(id: String)
// Relatives
static func getRelatives(by: T) -> [K]?
static func get(byRelative: K) -> [T]?
}
extension DataManager {
static func getAll(sorted: [NSSortDescriptor]?, context: NSManagedObjectContext) -> [T]? {
guard let fetchRequest: NSFetchRequest<T> = T.fetchRequest() as? NSFetchRequest<T> else { return nil }
fetchRequest.sortDescriptors = sorted
var results: [T]? = nil
do {
results = try context.fetch(fetchRequest)
} catch {
assert(false, error.localizedDescription)
} //TODO: Handle Errors
return results
}
}
protocol Identifiable {
typealias Identity = String
var id: Identity? { get }
}
extension DataManager where Self.T: Identifiable {
static func get(by id: T.Identity, context: NSManagedObjectContext) -> T? {
guard let fetchRequest: NSFetchRequest<T> = T.fetchRequest() as? NSFetchRequest<T> else { return nil }
fetchRequest.predicate = NSPredicate(format: "%K == %@", "id", id)
var rawResults: [T]? = nil
do {
rawResults = try context.fetch(fetchRequest)
} catch {
assert(false, error.localizedDescription)
} //TODO: Handle Errors
if let result = rawResults?.first {
return result }
else { return nil }
}
}
答案 0 :(得分:0)
好吧,我已经创建了一个解决方案。 我们可以识别与特定班级的所有关系:
let relationships = T.entity().relationships(forDestination: K.entity())
它允许我们为每个关系找到项目的所有ID(我们可以为同一个相对实体建立多个关系):
let relativesIDs = item.objectIDs(forRelationshipNamed: relationship.name)
因此,我们可以使用这些ID从另一个类中获取记录。
static func getRelatives(of item: T, context:NSManagedObjectContext) -> [K]? {
guard let fetchRequest: NSFetchRequest<K> = K.fetchRequest() as? NSFetchRequest<K> else { return nil }
fetchRequest.fetchBatchSize = 100
var results: [K]? = nil
var resultSet: Set<K> = [] // doesn't allow duplicates
let relationships = T.entity().relationships(forDestination: K.entity())
for relationship in relationships {
let relativesIDs = item.objectIDs(forRelationshipNamed: relationship.name)
let predicate = NSPredicate(format: "self IN %@", relativesIDs)
fetchRequest.predicate = predicate
var batchResults: [K] = []
do {
batchResults = try context.fetch(fetchRequest)
} catch {
assert(false, error.localizedDescription)
} //TODO: Handle Errors
if batchResults.count > 0 { resultSet = resultSet.union(Set(batchResults)) }
}
if resultSet.count > 0 { results = Array(resultSet) }
return results
}
我不确定这是最优雅的解决方案,但它有效: - )