谓词未应用于Core Data中的fetchRequest

Question

我正在core data使用swift 3.0。在我的核心数据中，我有一个实体＆＃39;用户＆＃39;有三个属性＆＃39; name＆＃39; ，age和＆＃39;地址＆＃39;定义为String。

我想在core data entity中检查用户名是否已存在。我的代码是

func checkUserAlreadyExists(name:String) -> Bool
    {

        let appDelegate = UIApplication.shared.delegate as? AppDelegate
        let managedContext = appDelegate?.persistentContainer.viewContext
        let fetchRequest = NSFetchRequest<UserModel>(entityName: "User")
        fetchRequest.predicate = NSPredicate(format: "name = %@",name)
//I have also tried this 
//fetchRequest.predicate = NSPredicate(format: "name == %@",name)

        do {
            let arrUsers:[UserModel] = try managedContext!.fetch(fetchRequest)
            print(arrUsers.count)
            if(arrUsers.count>0)
            {
               return true
            }
            else
            {
                return false
            }
        } catch let error as NSError {
            print("Could not fetch. \(error), \(error.userInfo)")
            return false
        }

    }

我刚刚输入了一个名为 test 的对象，但它没有提取， arrUsers.count 总是返回 0 。< / p>

我在下面的代码中插入数据

guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {return}

            let managedContext = appDelegate.persistentContainer.viewContext
            let entity = NSEntityDescription.entity(forEntityName: "User",in: managedContext)!

            let user:UserModel = NSManagedObject(entity: entity,insertInto: managedContext) as! UserModel
            user.name = "test"
            user.address = "test address"
            user.age = "25"


            do {
                try managedContext.save()
                getAllUsersFromCoreData()

            } catch let error as NSError
            {
                print("Could not save. \(error), \(error.userInfo)")
            }

我在Questions上经历了很多stackoverflow，但没有找到解决方案