核心数据:删除实体所有实例的最快方法

Question

我正在使用Core Data在本地持久保存Web服务调用的结果.Web服务返回完整的对象模型,比方说,"汽车" - 可能是大约2000个(我不能让Web服务返回任何小于1或所有汽车.

下次打开我的应用程序时,我想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.

是否有更快的方法来清除托管对象上下文中特定实体的所有实例(例如"CAR"类型的所有实体),或者我是否需要查询它们,然后遍历结果以删除每个实例,然后保存？

理想情况下,我可以说删除所有实体是Blah的地方.

Answer 1

iOS 9及更高版本:

iOS 9添加了一个名为的新类NSBatchDeleteRequest,它允许您轻松删除与谓词匹配的对象,而无需将它们全部加载到内存中.这是你如何使用它:

斯威夫特2

let fetchRequest = NSFetchRequest(entityName: "Car")
let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)

do {
    try myPersistentStoreCoordinator.executeRequest(deleteRequest, withContext: myContext)
} catch let error as NSError {
    // TODO: handle the error
}

Objective-C的

NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Car"];
NSBatchDeleteRequest *delete = [[NSBatchDeleteRequest alloc] initWithFetchRequest:request];

NSError *deleteError = nil;
[myPersistentStoreCoordinator executeRequest:delete withContext:myContext error:&deleteError];

有关批量删除的更多信息可以在WWDC 2015的"核心数据中的新内容"会话中找到(从~14:10开始).

iOS 8及更早版本:

获取所有并删除所有:

NSFetchRequest *allCars = [[NSFetchRequest alloc] init];
[allCars setEntity:[NSEntityDescription entityForName:@"Car" inManagedObjectContext:myContext]];
[allCars setIncludesPropertyValues:NO]; //only fetch the managedObjectID

NSError *error = nil;
NSArray *cars = [myContext executeFetchRequest:allCars error:&error];
[allCars release];
//error handling goes here
for (NSManagedObject *car in cars) {
  [myContext deleteObject:car];
}
NSError *saveError = nil;
[myContext save:&saveError];
//more error handling here

Answer 2

在Swift 3中重置实体:

func resetAllRecords(in entity : String) // entity = Your_Entity_Name
    {

        let context = ( UIApplication.shared.delegate as! AppDelegate ).persistentContainer.viewContext
        let deleteFetch = NSFetchRequest<NSFetchRequestResult>(entityName: entity)
        let deleteRequest = NSBatchDeleteRequest(fetchRequest: deleteFetch)
        do
        {
            try context.execute(deleteRequest)
            try context.save()
        }
        catch
        {
            print ("There was an error")
        }
    }

Answer 3

更清洁和通用:添加此方法:

- (void)deleteAllEntities:(NSString *)nameEntity
{
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:nameEntity];
    [fetchRequest setIncludesPropertyValues:NO]; //only fetch the managedObjectID

    NSError *error;
    NSArray *fetchedObjects = [theContext executeFetchRequest:fetchRequest error:&error];
    for (NSManagedObject *object in fetchedObjects)
    {
        [theContext deleteObject:object];
    }

    error = nil;
    [theContext save:&error];
}

Answer 4

对于Swift 2.0:

class func clearCoreData(entity:String) {
  let fetchRequest = NSFetchRequest()
  fetchRequest.entity = NSEntityDescription.entityForName(entity, inManagedObjectContext: moc!)
  fetchRequest.includesPropertyValues = false
  do {
    if let results = try moc!.executeFetchRequest(fetchRequest) as? [NSManagedObject] {
      for result in results {
        moc!.deleteObject(result)
      }

      try moc!.save()
    }
  } catch {
    LOG.debug("failed to clear core data")
  }
}

Answer 5

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)")
}

Answer 6

这是一个与此处类似的问题,有人建议设置关系删除规则,因此您只需要删除一个对象.因此,如果您拥有或可以创建与汽车具有多对多关系的实体,并在删除较高实体时将删除规则设置为级联,则所有汽车也将被删除.这可以节省一些处理时间,因为您不必执行加载所有汽车所涉及的步骤.在更大的数据集中,这可能是绝对必要的.

Answer 7

已经发布了一个很好的答案,这只是一个推荐!

一个好方法是只添加一个类别NSManagedObject并实现一个像我一样的方法:

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

...你唯一需要的是从app delegate获取managedObjectContext,或者你拥有它的每一个;)

之后你可以像以下一样使用它:

[NSManagedObject deleteAllFromEntity:@"EntityName"];

进一步优化可能是您删除了实体名称的参数,而是从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

用法然后:

[managedObjectContext deleteAllFromEntity:@"EntityName"];

Answer 8

Swift 4，iOS 12和Xcode 10更新

100％工作只是剪切和粘贴

只需将此函数放在相关的类中，
然后在函数或按钮的任何位置或任何位置或任何位置调用此函数self.deleteData()，viewDidLoad()

以便通过单击按钮来删除实体中的所有数据，并将“ myEntity”替换为您在实体中定义的实体核心数据

func deleteData() {

let appDel:AppDelegate = (UIApplication.shared.delegate as! AppDelegate)
let context:NSManagedObjectContext = appDel.persistentContainer.viewContext
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "myEntity")
    fetchRequest.returnsObjectsAsFaults = false

    do
    {
        let results = try context.fetch(fetchRequest)
        for managedObject in results
        {
            let managedObjectData:NSManagedObject = managedObject as! NSManagedObject
            context.delete(managedObjectData)
        }
    } catch let error as NSError {
        print("Deleted all my data in myEntity error : \(error) \(error.userInfo)")
    }
}

Answer 9

Swift 4, iOS 10+
静态函数，可以申请任何实体删除其所有数据

protocol NSManagedObjectHelper {
}
extension NSManagedObject: NSManagedObjectHelper {
}
extension NSManagedObjectHelper where Self: NSManagedObject {
    static func removeAllObjectsInContext(_ managedContext: NSManagedObjectContext) {
        let request: NSFetchRequest = NSFetchRequest(entityName: String(describing: self))
        let deleteRequest = NSBatchDeleteRequest(fetchRequest: request)
        do {
            deleteRequest.resultType = .resultTypeObjectIDs//to clear objects from memory
            let result = try managedContext.execute(deleteRequest) as? NSBatchDeleteResult
            if let objectIDArray = result?.result as? [NSManagedObjectID] {
                let changes = [NSDeletedObjectsKey : objectIDArray]
                /*By calling mergeChangesFromRemoteContextSave, all of the NSManagedObjectContext instances that are referenced will be notified that the list of entities referenced with the NSManagedObjectID array have been deleted and that the objects in memory are stale. This causes the referenced NSManagedObjectContext instances to remove any objects in memory that are loaded which match the NSManagedObjectID instances in the array.*/
                NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [managedContext])
            }
            try managedContext.save()
        } catch let error {
            print(error)
        }
    }
}

“房间”是一个实体

Room.removeAllObjectsInContext(self.persistentContainer.viewContext)

编辑于 20191025：如果我们在同一项目中使用多个目标，“Self.fetchRequest()”指令可能会导致问题。因此替换为 NSFetchRequest(entityName: String(describing: self))

Answer 10

iOS 10 及更高版本

适用于所有版本。传递实体名称并遍历以​​删除所有条目并保存上下文。

func deleteData(entityToFetch: String, completion: @escaping(_ returned: Bool) ->()) {
        let context = NSManagedObjectContext()
        context = your managedObjectContext

        let fetchRequest = NSFetchRequest<NSFetchRequestResult>()
        fetchRequest.entity = NSEntityDescription.entity(forEntityName: entityToFetch, in: context)
        fetchRequest.includesPropertyValues = false
         do {   
            let results = try context.fetch(fetchRequest) as! [NSManagedObject]
            for result in results {
                context.delete(result)
            }
            try context.save()
            completion(true)
        } catch {
            completion(false)
            print("fetch error -\(error.localizedDescription)")
        }
    }

Answer 11

Swift 3.X和Swift 4.X，简便的方法。仅更改YourTable

    let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "YourTable")
    fetchRequest.returnsObjectsAsFaults = false

    do
    {
        let results = try context.fetch(fetchRequest)
        for managedObject in results
        {
            let managedObjectData:NSManagedObject = managedObject as! NSManagedObject
            context.delete(managedObjectData)
        }
    } catch let error as NSError {
        print("Detele all my data in \(entity) error : \(error) \(error.userInfo)")
    }