将对象数组保存到 Core Data

Posted 2023-02-27

【中文标题】将对象数组保存到 Core Data

【英文标题】：Saving an array of objects to Core Data

【发布时间】：2018-03-09 14:21:35

【问题描述】：

我有一个 [User] 类型的数组，我想将它保存在 Core Data 中，然后在表格视图中显示它。以下是我保存和检索数据的函数：

func saveUserData(_ users: [User]) 
    let context = appDelegate.persistentContainer.viewContext
    let newUser = NSEntityDescription.insertNewObject(forEntityName: "Users", into: context)
    for user in users 
        newUser.setValue(user.id, forKey: "id")
        newUser.setValue(user.name, forKey: "name")
        newUser.setValue(user.email, forKey: "email")
        newUser.setValue(user.phone, forKey: "phone")
        newUser.setValue(user.website, forKey: "website")
        newUser.setValue(user.city, forKey: "city")
        newUser.setValue(user.lat, forKey: "lat")
        newUser.setValue(user.long, forKey: "long")
    
    do 
        try context.save()
        print("Success")
     catch 
        print("Error saving: \(error)")
    


func retrieveSavedUsers() -> [User]? 
    let context = appDelegate.persistentContainer.viewContext
    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Users")
    request.returnsObjectsAsFaults = false
    var retrievedUsers: [User] = []
    do 
        let results = try context.fetch(request)
        if !results.isEmpty 
            for result in results as! [NSManagedObject] 
                guard let id = result.value(forKey: "id") as? Int else  return nil 
                guard let name = result.value(forKey: "name") as? String else  return nil 
                guard let email = result.value(forKey: "email") as? String else  return nil 
                guard let phone = result.value(forKey: "phone") as? String else  return nil 
                guard let website = result.value(forKey: "website") as? String else  return nil 
                guard let city = result.value(forKey: "city") as? String else  return nil 
                guard let lat = result.value(forKey: "lat") as? String else  return nil 
                guard let long = result.value(forKey: "long") as? String else  return nil 
                let user = User(with: id, name: name, email: email, phone: phone, website: website, city: city, lat: lat, long: long)
                retrievedUsers.append(user)
            
        
     catch 
        print("Error retrieving: \(error)")
    
    return retrievedUsers

检索工作正常，但问题是它只保存了 Core Data 中最后一个 User 类型的对象。似乎当我在保存用户时迭代用户时，每次迭代都会覆盖用户对象而不是保存一个新对象。知道如何解决这个问题，或者有没有更好的方法将自定义对象数组保存到 Core Data 中？

【问题讨论】：

很好的答案，我想问一下，“User”类型是声明为普通类还是NSM​​anagedObject？

@bellaGU 用户定义如下class User: Mappable

【参考方案1】：

您只创建一个用户实体，然后每次都对其进行重写。问题是，就在您遍历用户数组之前，您创建了一个新实体。 您应该为数组中的每个用户都这样做。这是一个非常简单的解决方法，只需交换两行。正确代码见下：

func saveUserData(_ users: [User]) 
    let context = appDelegate.persistentContainer.viewContext
    for user in users 
        let newUser = NSEntityDescription.insertNewObject(forEntityName: "Users", into: context)
        newUser.setValue(user.id, forKey: "id")
        newUser.setValue(user.name, forKey: "name")
        newUser.setValue(user.email, forKey: "email")
        newUser.setValue(user.phone, forKey: "phone")
        newUser.setValue(user.website, forKey: "website")
        newUser.setValue(user.city, forKey: "city")
        newUser.setValue(user.lat, forKey: "lat")
        newUser.setValue(user.long, forKey: "long")
    
    do 
        try context.save()
        print("Success")
     catch 
        print("Error saving: \(error)")