核心数据无法持久保存对象 [英] Core Data not saving objects persistently

问题描述

我是Core Data的新手，因此不确定自己是否犯错。我已经从REST API下载了一些数据，并且成功将 JSON 响应保存到磁盘。我正在尝试处理数据并使用Core Data永久保存。

I'm new to Core Data and as such am not sure if I'm making a mistake. I've downloaded some data from a REST API and it successfully saves the JSON response to disk. I'm trying to process the data and save it persistently using Core Data.

NSLog(@"inserted objects: %@", [managedObjectContext insertedObjects]);
    [managedObjectContext performBlockAndWait:^{
        NSError *error = nil;
        if (![managedObjectContext save:&error]) {
            NSLog(@"Unable to save context for class %@", className);
        } else {
            NSLog(@"saved all records!");
        }
    }];

我已经成功处理了 JSON 并将其添加到 NSManagedObjectContext 中。在第一行中，它表明我已成功尝试插入2个对象。

I've successfully processed the JSON and added it to an NSManagedObjectContext. In the first line, it shows that I've successfully attempted to insert 2 objects.

inserted objects: {(
    <User: 0xa259af0> (entity: User; id: 0xa259b70 <x-coredata:///User/t44BB97D0-C4B4-4BA6-BD25-13CEFDAE665F3> ; data: {
    email = "[e-mail]";
    experience = "2013-07-20";
    "first_name" = Vishnu;
    id = 2;
    "job_title" = Developer;
    "last_name" = Prem;
    location = "";
    "phone_number" = "[phone]";
    "profile_pic" = "";
    "thumbnail_profile_pic" = "";
    "user_id" = 2;
}),
    <User: 0xa25e460> (entity: User; id: 0xa25e4c0 <x-coredata:///User/t44BB97D0-C4B4-4BA6-BD25-13CEFDAE665F2> ; data: {
    email = "[e-mail]";
    experience = "2013-07-20";
    "first_name" = Sanchit;
    id = 1;
    "job_title" = Developer;
    "last_name" = Bareja;
    location = "";
    "phone_number" = "[phone]";
    "profile_pic" = "";
    "thumbnail_profile_pic" = "";
    "user_id" = 1;
})
)}

当我尝试 [managedObjectContext save：& error] ，它可以成功完成并按预期打印出保存的所有记录。但是，当我转到应用程序 .sqlite 文件并检查添加的对象时，我意识到它尚未向数据库添加任何对象。

When I attempted [managedObjectContext save:&error], it does so successfully and print out "saved all records" as expected. However, when I go to my application .sqlite file and check for added objects, I realize that it hasn't added any objects to the db.

在重新启动应用程序时，我打印出数据库中已经存在的对象列表，并确认我尚未保存任何对象。

On app relaunch, I print out a list of objects that are already in the database and it confirms that I've none saved yet.

有人知道发生了什么事，为什么即使我看起来已经成功创建了需要的用户对象，我也无法永久保存数据？

Does anyone know what's going on and why I'm not able to save the data persistently even though it looks like I've successfully created the 'User' objects that needs to be saved in the Core Data model.

编辑：

在这里创建 NSPersistentStoreCoordinator

// Returns the persistent store coordinator for the application.
// If the coordinator doesn't already exist, it is created and the application's store added to it.
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (_persistentStoreCoordinator != nil) {
        return _persistentStoreCoordinator;
    }

    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"RTModel.sqlite"];

    NSError *error = nil;
    NSLog(@"Test 1");
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    NSLog(@"Test 2");

    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
        /*
         Replace this implementation with code to handle the error appropriately.

         abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.

         Typical reasons for an error here include:
         * The persistent store is not accessible;
         * The schema for the persistent store is incompatible with current managed object model.
         Check the error message to determine what the actual problem was.


         If the persistent store is not accessible, there is typically something wrong with the file path. Often, a file URL is pointing into the application's resources directory instead of a writeable directory.

         If you encounter schema incompatibility errors during development, you can reduce their frequency by:
         * Simply deleting the existing store:
         [[NSFileManager defaultManager] removeItemAtURL:storeURL error:nil]

         * Performing automatic lightweight migration by passing the following dictionary as the options parameter:
         [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

         Lightweight migration will only work for a limited set of schema changes; consult "Core Data Model Versioning and Data Migration Programming Guide" for details.

         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return _persistentStoreCoordinator;
}

我有3个上下文。

• masterManagedObjectContext

backgroundManagedObjectContext

newManagedObjectContext

master是背景和新背景的父对象。当我查询这样的上下文时：

master is parent of both background and new. When I query the contexts like this:

    NSError *error = nil;
    NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"User"];
    [request setSortDescriptors:[NSArray arrayWithObject:
                                 [NSSortDescriptor sortDescriptorWithKey:@"id" ascending:YES]]];
    [request setReturnsObjectsAsFaults:NO];
    NSArray *testArray = [[[RTCoreDataController sharedInstance] newManagedObjectContext] executeFetchRequest:request error:&error];

    for (User *obj in testArray) {
        NSLog(@"obj.id %@", obj.id);
    }

    NSLog(@"query records: %@",testArray);

master和background都在NSLog中返回正确的obj.id并给出以下输出@查询记录

master and background both return the correct obj.id in the NSLog as well as gives the output below for @"query records"

   (
    "<User: 0xa3811d0> (entity: User; id: 0xa381230 <x-coredata:///User/t92BCED2D-CD17-49CC-9EBA-DF8F52F06A002> ; data: {\n    email = \"[e-mail]\";\n    experience = \"2013-07-20\";\n    \"first_name\" = Sanchit;\n    id = 1;\n    \"job_title\" = Developer;\n    \"last_name\" = Bareja;\n    location = \"\";\n    \"phone_number\" = \"[phone]\";\n    \"profile_pic\" = \"\";\n    \"thumbnail_profile_pic\" = \"\";\n    \"user_id\" = 1;\n})",
    "<User: 0xa382170> (entity: User; id: 0xa3820b0 <x-coredata:///User/t92BCED2D-CD17-49CC-9EBA-DF8F52F06A003> ; data: {\n    email = \"[e-mail]\";\n    experience = \"2013-07-20\";\n    \"first_name\" = Vishnu;\n    id = 2;\n    \"job_title\" = Developer;\n    \"last_name\" = Prem;\n    location = \"\";\n    \"phone_number\" = \"[phone]\";\n    \"profile_pic\" = \"\";\n    \"thumbnail_profile_pic\" = \"\";\n    \"user_id\" = 2;\n})"
)

但是 new返回（null） 表示 NSLog 中的obj.id，并返回 @查询记录 的以下内容：

however "new" returns (null) for the obj.id in NSLog and returns the following for @"query records":

(
    "<User: 0xa2b08a0> (entity: User; id: 0x95aebe0 <x-coredata:///User/tBFCC6C5F-7D2C-4AA0-BA96-B806EE360A762> ; data: <fault>)",
    "<User: 0xa2b0910> (entity: User; id: 0xa4b9780 <x-coredata:///User/tBFCC6C5F-7D2C-4AA0-BA96-B806EE360A763> ; data: <fault>)"
)

推荐答案

从代码和注释看来，您似乎没有保存主上下文。确保调用了

From your code and the comments it seems that you are not saving the master context. Make sure you call

[managedObjectContext save:&error]; 

在所有保存数据的子上下文中，以及 after 在主上下文中。

on all child contexts that save the data, and after that on the master context as well.

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