ios - 在保存到 coredata -Swift 之前检查数据是否存在

Question

保存数据时，检查数据是否已存在于实体中。这里的问题是上面的方法没有按预期工作，当我第一次运行应用程序时，它显示数据已经存在。请检查下面的代码并阐明一些情况。谢谢。

func someEntityExists(id: String, entityName: String, type : String, fieldName : String) -> Bool {
    let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: entityName)
    if type == "String"{
    fetchRequest.predicate = NSPredicate(format: "\(fieldName) == %@", id)
    }else{
        fetchRequest.predicate = NSPredicate(format: "\(fieldName) == %d", id)

    }

    var results: [NSManagedObject] = []

    do {
        results = try self.persistentContainer.viewContext.fetch(fetchRequest)
    }
    catch {
        print("error executing fetch request: \(error)")
    }

    return results.count > 0
}

下面是调用此函数来保存用户信息的代码。

  func saveUserInfo(detail:[String:Any])-> Bool
{
    let context = self.persistentContainer.viewContext
    var isSave : Bool = false
    let entity = NSEntityDescription.entity(forEntityName: "User", in: context)
    let newUser = NSManagedObject(entity: entity!, insertInto: context)
    newUser.setValue(detail["id"], forKey: "id")
    newUser.setValue(detail["api_token"], forKey: "api_token")
    newUser.setValue(detail["username"], forKey: "username")
    newUser.setValue(detail["email"], forKey: "email")
    if let category = detail["firstname"] as? String {
        newUser.setValue(detail["firstname"], forKey: "firstname")
    }
    if let category = detail["middlename"] as? String {
        newUser.setValue(detail["middlename"], forKey: "middlename")
    }
    if let category = detail["lastname"] as? String {
        newUser.setValue(detail["lastname"], forKey: "lastname")
    }

    do {

        let isExist = someEntityExists(id: newUser.value(forKey:        "email") as! String , entityName: "User", type: "String", fieldName: "email")
        if isExist == true {
            // don't save anything
            print("Data is already present  ")
        }else{
        try context.save()
        isSave  = true
        }
    } catch {

        print("Failed saving")
        isSave  = false
    }



    return isSave

}

Answer 1

首先，您在调用 someEntityExists 之前在托管上下文中创建一个 User 对象，因此该对象很可能会包含在提取中，即使尚未保存。

在创建新用户实体之前调用 someEntityExists 来查看是否应该继续

func saveUserInfo(detail:[String:Any])-> Bool {
    if someEntityExists(id: detail["email"] , entityName: "User", type: "String", fieldName: "email") {
        print("Data is already present")
         return false
    }
    //else create and save new user
}