我使用Core Data在本地持久化Web服务调用的结果。web服务返回完整的对象模型，比如说，“Cars”——可能有2000辆车(我不能让web服务返回小于1辆或ALL辆的任何东西。
下次打开应用程序时，我希望通过再次调用所有汽车的Web服务来刷新Core Data持久化副本，但是为了防止重复，我需要首先清除本地缓存中的所有数据。
是否有一种更快的方法来清除管理对象上下文中特定实体的所有实例(例如，类型为“CAR”的所有实体)，或者我需要查询它们调用，然后遍历结果删除每个，然后保存?
理想情况下，我可以说删除实体所在的所有地方等等。
当前回答
Dave Delongs的Swift 2.0回答让我崩溃了(在iOS 9中)
但这个方法奏效了:
let fetchRequest = NSFetchRequest(entityName: "Car")
let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
do {
try managedObjectContext.executeRequest(deleteRequest)
try managedObjectContext.save()
}
catch let error as NSError {
// Handle error
}
其他回答
迅速:
let fetchRequest = NSFetchRequest()
fetchRequest.entity = NSEntityDescription.entityForName(entityName, inManagedObjectContext: context)
fetchRequest.includesPropertyValues = false
var error:NSError?
if let results = context.executeFetchRequest(fetchRequest, error: &error) as? [NSManagedObject] {
for result in results {
context.deleteObject(result)
}
var error:NSError?
if context.save(&error) {
// do something after save
} else if let error = error {
println(error.userInfo)
}
} else if let error = error {
println("error: \(error)")
}
在Swift 3.0中
func deleteAllRecords() {
//delete all data
let context = appDelegate.persistentContainer.viewContext
let deleteFetch = NSFetchRequest<NSFetchRequestResult>(entityName: "YourClassName")
let deleteRequest = NSBatchDeleteRequest(fetchRequest: deleteFetch)
do {
try context.execute(deleteRequest)
try context.save()
} catch {
print ("There was an error")
}
}
iOS 9.0及以上版本:
NSBatchDeleteRequest用于删除核心数据中的记录。它的工作速度非常快，从一个实体删除所有记录所需的时间更少。它需要NSFetchRequest作为参数。如果你想从一个实体删除所有记录，你可以使用它，它为我工作。
let manageObject:NSManagedObjectContext = appDelegateObject.managedObjectContext
let fetchRequest = NSFetchRequest(entityName: “EnityName”)
let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
let persistCor:NSPersistentStoreCoordinator = appDelegateObject.persistentObject
do {
try persistCor.executeRequest(deleteRequest, withContext: manageObject)
try manageObject.save()
} catch {
print(error?.localizedDescription)
}
如果实体包含很多条目，最好的方法是这样，因为它节省内存
- (void)deleteAll:(NSManagedObjectContext *)managedObjectContext entityName:(NSString *)entityName
{
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[managedObjectContext setUndoManager:nil];
NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setIncludesPropertyValues:NO];
[fetchRequest setFetchLimit:100]; // you can change this number if you want
NSError *error;
NSArray *items = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
while ([items count] > 0) {
@autoreleasepool {
for (NSManagedObject *item in items) {
[managedObjectContext deleteObject:item];
}
if (![managedObjectContext save:&error]) {
NSLog(@"Error deleting %@ - error:%@",self.entityName, error);
}
}
items = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
}
}
func deleteAll(entityName: String) {
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: entityName)
let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
deleteRequest.resultType = .resultTypeObjectIDs
guard let context = self.container?.viewContext
else { print("error in deleteAll")
return }
do {
let result = try context.execute(deleteRequest) as? NSBatchDeleteResult
let objectIDArray = result?.result as? [NSManagedObjectID]
let changes: [AnyHashable : Any] = [NSDeletedObjectsKey : objectIDArray as Any]
NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [context])
} catch {
print(error.localizedDescription)
}
}
