xcode 此 NSPersistentStoreCoordinator 没有持久存储（架构不匹配或迁移失败）。它无法执行保存操作

This NSPersistentStoreCoordinator has no persistent stores (schema mismatch or migration failure). It cannot perform a save operation

提问by Uzair Dhada

I am working on a application in which we are using x.x.xcdatamodel. Now in same x.x.xcdatamodel I have added an attribute in one of the entity. The application crashes showing the message "This NSPersistentStoreCoordinator has no persistent stores (schema mismatch or migration failure). It cannot perform a save operation.". I tried many things and i am also using lightweight migration to handle the situation but that is not working as well.Below is my code:

我正在开发一个使用 xxxcdatamodel 的应用程序。现在在同一个 xxxcdatamodel 中，我在实体之一中添加了一个属性。应用程序崩溃并显示消息“此 NSPersistentStoreCoordinator 没有持久存储（架构不匹配或迁移失败）。它无法执行保存操作。”。我尝试了很多事情，我也在使用轻量级迁移来处理这种情况，但这并不奏效。下面是我的代码：

    - (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (__persistentStoreCoordinator != nil)
    {
        return __persistentStoreCoordinator;
    }

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

    NSError *error = nil;
    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];

    NSDictionary *options = @{
                              NSMigratePersistentStoresAutomaticallyOption : @YES,
                              NSInferMappingModelAutomaticallyOption : @YES,
                              NSSQLitePragmasOption : @{@"journal_mode" : @"DELETE"}
                              };

    if(![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:options error:&error])
    {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    }

    return __persistentStoreCoordinator;
}




- (BOOL) saveContext
{
    @synchronized (_localStorage) {
        //NSLog(@"----------------------------Save context called---------------------------");
        BOOL result = TRUE;
        NSError *error = nil;
        NSManagedObjectContext *managedObjectContext = self.managedObjectContext;

        if (managedObjectContext != nil)
        {
            //Crashes here at this line.
            if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error])
            {
                NSLog(@"----------------------------Save context failed---------------------------");
                result = FALSE;
                NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            }
        }

        //NSLog(@"----------------------------Save context completed---------------------------");

        return result;
    }
}

Am i missing something over here? OR Is it like i have to perform complete migration even if i add a single attribute in an entity?Thanks in advance.

我在这里错过了什么吗？或者，即使我在实体中添加单个属性，我是否也必须执行完整迁移？提前致谢。

回答by Tom Harrington

You don't have to do the migration yourself here. You dohave to add a new version of the data model. You can't edit the xcdatamodeland expect Core Data to just use the new version. You need to keep your existing model, create a new version, and make your changes in the new version. You must always have a version of the model that matches the persistent store file.

您不必在这里自己进行迁移。你也必须添加数据模型的新版本。您不能编辑xcdatamodel并期望 Core Data 只使用新版本。您需要保留现有模型、创建新版本并在新版本中进行更改。您必须始终拥有与持久存储文件匹配的模型版本。

You create a new version by selecting the xcdatamodelmodel file in Xcode's file browser, going to the "Editor" menu, and selecting "Add Model Version..."

您可以通过xcdatamodel在 Xcode 的文件浏览器中选择模型文件，转到“编辑器”菜单，然后选择“添加模型版本...”来创建新版本。

回答by Ali Baqbani

I work on a project and faced a similar problem, it seems that the former developer forgot to pass these two options for a lightweight migration. I passed in the second one and the migration completed successfully.

我在做一个项目，遇到了类似的问题，之前的开发者好像忘记通过这两个选项进行轻量级迁移了。我通过了第二个，迁移成功完成。

You request automatic lightweight migration using the options dictionary you pass in addPersistentStoreWithType:configuration:URL:options:error:, by setting values corresponding to both the NSMigratePersistentStoresAutomaticallyOptionand the NSInferMappingModelAutomaticallyOptionkeys to YES:

您可以使用传入的选项字典请求自动轻量级迁移addPersistentStoreWithType:configuration:URL:options:error:，方法是将与NSMigratePersistentStoresAutomaticallyOption和NSInferMappingModelAutomaticallyOption键对应的值设置为YES：

NSError *error = nil;
NSURL *storeURL = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@"momd"];
NSPersistentStoreCoordinator *psc = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:managedObjectModel]
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

BOOL success = [psc addPersistentStoreWithType:NSSQLiteStoreType
                configuration:nil URL:storeURL
                options:options error:&error];
if (!success) {
  // Handle the error.
}