快速清除DB中的所有对象:

func purgeAllData() {
    let uniqueNames = persistentContainer.managedObjectModel.entities.compactMap({ $0.name })

    uniqueNames.forEach { (name) in
      let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: name)
       let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
         do {
        try persistentContainer.viewContext.execute(batchDeleteRequest)
      } catch {
        let nserror = error as NSError
        fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
      }
   }
 }

NSBatchDeleteRequest Swift 5.5和Xcode 13.2

删除SQLite持久存储中的对象，而不加载到内存中。在持久存储上执行的更改不会反映在当前内存中的对象中。

执行批量删除之后，从持久存储中删除内存中的所有对象。

下面是执行batchDeleteRequest的一些方便的扩展方法

extension NSManagedObject {
    
    private static var entityName: String {
        return String(describing: self)
    }
    
    static func fetchRequest<Self>(
        with predicate: NSPredicate? = nil,
        configureBlock: ((NSFetchRequest<Self>) -> Void)? = nil
    ) -> NSFetchRequest<Self> where Self: NSFetchRequestResult {
        let request = NSFetchRequest<Self>(entityName: entityName)
        request.predicate = predicate
        configureBlock?(request)
        return request
    }
    
    static func batchDelete(with fetchRequest: NSFetchRequest<NSFetchRequestResult>,
                            in context: NSManagedObjectContext) {
        let batchDeteleRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
        batchDeteleRequest.resultType = .resultTypeObjectIDs
        do {
            if let fetchResult = try context.execute(batchDeteleRequest) as? NSBatchDeleteResult,
               let deletedManagedObjectIds = fetchResult.result as? [NSManagedObjectID], !deletedManagedObjectIds.isEmpty {
                let changes = [NSDeletedObjectsKey: deletedManagedObjectIds]
                NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [context])
            }
        } catch {
            print("Error while executing batchDeleteRequest: \(error.localizedDescription)")
        }
    }
}

示例:我们可以通过传递fetchRequest调用batchDelete静态方法批量删除实体

class Entity: NSManagedObject {
    @NSManaged var name: String?
    @NSManaged var value: String?
}

extension Entity {
    
    static func executeBatchDelete(in context: NSManagedObjectContext) {
        let predicate = NSPredicate(format: "\(#keyPath(Entity.value)) == %@)", "abc")
        let deleteRequest: NSFetchRequest<NSFetchRequestResult> = Entity.fetchRequest(with: predicate)
        Entity.batchDelete(with: deleteRequest, in: context)
    }
}

为什么不将接收到的数据与现有缓存一起折叠呢?否则它就不是真正的“刷新”，而是“重新开始”，你也可以删除SQLLite文件并重新开始(假设你没有持久化其他数据)。

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)
    }

斯威夫特3。X和Swift 4。X，简单。只改变你的表格

    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)")
    }

Swift 4, iOS 10+ 静态函数，可以应用于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)

在20191025编辑:如果我们在同一个项目中使用多个目标，"Self.fetchRequest()"指令可能会导致问题。所以替换为NSFetchRequest(entityName: String(description: self))