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))

迅捷用户界面

从实体中获取实例，然后循环删除每个实例。

@Environment(\.managedObjectContext) var moc
    
@FetchRequest(sortDescriptors: []) var wizards: FetchedResults<Wizard>

var body: some View {
    VStack {
        List() { }

        Button("Delete all") {
            for wizard in wizards {
                moc.delete(wizard)
            }
            
            if moc.hasChanges {
                try? moc.save()
            }
        }
    }
}

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)。

    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)
    }
}

iOS 10及以上版本

适用于所有版本。传递实体名称并遍历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)")
        }
    }

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
    }