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
这段代码适用于iOS 9及以下版本
class func deleteAllRecords(in entity : String) // entity = Your_Entity_Name
{
let context = CoreDataStack.getContext() // Note:- Replace your context here with CoreDataStack.getContext()
let deleteFetch = NSFetchRequest<NSFetchRequestResult>(entityName: entity)
if #available(iOS 9, *)
{
let deleteRequest = NSBatchDeleteRequest(fetchRequest: deleteFetch)
do
{
try context.execute(deleteRequest)
try context.save()
}
catch
{
print("There was an error:\(error)")
}
}
else
{
do{
let deleteRequest = try context.fetch(deleteFetch)
for anItem in deleteRequest {
context.delete(anItem as! NSManagedObject)
}
}
catch
{
print("There was an error:\(error)")
}
}
CoreDataStack.saveContext() // Note:- Replace your savecontext here with CoreDataStack.saveContext()
}
其他回答
OOP方式，没有任何字符串作为实体名称 Swift 3+， Xcode 10+
func batchDelete<T>(in context: NSManagedObjectContext, fetchRequest: NSFetchRequest<T>) throws {
guard let request = fetchRequest as? NSFetchRequest<NSFetchRequestResult> else {
throw ErrorService.defaultError
}
let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: request)
do {
try context.execute(batchDeleteRequest)
} catch {
throw error
}
}
然后调用do/catch块
let fetchRequest: NSFetchRequest<YourEntity> = YourEntity.fetchRequest()
do {
let data = try context.fetch(fetchRequest)
if data.count > 0 {
try self.batchDelete(in: context, fetchRequest: fetchRequest)
}
} catch {
// throw error
}
这是一个类似的问题，有人建议设置一个关系删除规则，这样你只需要删除一个对象。因此，如果您已经或可以创建一个与汽车具有多对关系的实体，并将删除规则设置为级联，当您删除更高的实体时，所有的汽车也将被删除。这可以节省一些处理时间，因为您不必执行加载所有汽车的步骤。在更大的数据集中，这可能是绝对必要的。
一个很好的答案已经贴出来了，这只是一个推荐!
一个好方法是添加一个类别到NSManagedObject和实现一个方法，就像我做的:
头文件(例如NSManagedObject+Ext.h)
@interface NSManagedObject (Logic)
+ (void) deleteAllFromEntity:(NSString*) entityName;
@end
代码文件:(例如NSManagedObject+Ext.m)
@implementation NSManagedObject (Logic)
+ (void) deleteAllFromEntity:(NSString *)entityName {
NSManagedObjectContext *managedObjectContext = [AppDelegate managedObjectContext];
NSFetchRequest * allRecords = [[NSFetchRequest alloc] init];
[allRecords setEntity:[NSEntityDescription entityForName:entityName inManagedObjectContext:managedObjectContext]];
[allRecords setIncludesPropertyValues:NO];
NSError * error = nil;
NSArray * result = [managedObjectContext executeFetchRequest:allRecords error:&error];
for (NSManagedObject * profile in result) {
[managedObjectContext deleteObject:profile];
}
NSError *saveError = nil;
[managedObjectContext save:&saveError];
}
@end
．.． 你唯一要做的就是从应用程序委托获取managedObjectContext，或者你在哪里都有它;)
之后你可以这样使用它:
[NSManagedObject deleteAllFromEntity:@"EntityName"];
进一步的优化可以是删除entityname的参数，而从clazzname获取名称。这将导致使用:
[ClazzName deleteAllFromEntity];
一个更干净的impl(作为NSManagedObjectContext的类别):
@implementation NSManagedObjectContext (Logic)
- (void) deleteAllFromEntity:(NSString *)entityName {
NSFetchRequest * allRecords = [[NSFetchRequest alloc] init];
[allRecords setEntity:[NSEntityDescription entityForName:entityName inManagedObjectContext:self]];
[allRecords setIncludesPropertyValues:NO];
NSError * error = nil;
NSArray * result = [self executeFetchRequest:allRecords error:&error];
for (NSManagedObject * profile in result) {
[self deleteObject:profile];
}
NSError *saveError = nil;
[self save:&saveError];
}
@end
那时的用法:
[managedObjectContext deleteAllFromEntity:@"EntityName"];
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")
}
}
这段代码适用于iOS 9及以下版本
class func deleteAllRecords(in entity : String) // entity = Your_Entity_Name
{
let context = CoreDataStack.getContext() // Note:- Replace your context here with CoreDataStack.getContext()
let deleteFetch = NSFetchRequest<NSFetchRequestResult>(entityName: entity)
if #available(iOS 9, *)
{
let deleteRequest = NSBatchDeleteRequest(fetchRequest: deleteFetch)
do
{
try context.execute(deleteRequest)
try context.save()
}
catch
{
print("There was an error:\(error)")
}
}
else
{
do{
let deleteRequest = try context.fetch(deleteFetch)
for anItem in deleteRequest {
context.delete(anItem as! NSManagedObject)
}
}
catch
{
print("There was an error:\(error)")
}
}
CoreDataStack.saveContext() // Note:- Replace your savecontext here with CoreDataStack.saveContext()
}
