首页 > 代码库 > 使用CoreData [3]

使用CoreData [3]

2024-07-15 00:14:08   221人阅读

使用CoreData [3]

此篇幅介绍CoreData如何升级版本防止崩溃

 

把你之前创建的实体文件全部删除掉,把沙盒中的数据库文件删除掉,实体只保持一个,然后重新创建出实体文件.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{    NSLog(@"%@", NSHomeDirectory());        // 创建两条记录    [self createStudent:@"YouXianMing" age:[NSNumber numberWithInt:26]];    [self createStudent:@"QiuLiang" age:[NSNumber numberWithInt:27]];        // 存储记录    [self saveContext];        // 设定要查询的实体    NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Student"];        // 取出查询结果    NSArray *students = [[self managedObjectContext] executeFetchRequest:fetch error:nil];    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {        Student *student = obj;        NSLog(@"%@ %@", student.age, student.name);    }];        return YES;}- (Student *)createStudent:(NSString *)name age:(NSNumber *)age{    // 实体描述信息    NSEntityDescription *description =     [NSEntityDescription entityForName:@"Student"                inManagedObjectContext:[self managedObjectContext]];        // 初始化对象    Student *student = [[Student alloc] initWithEntity:description                        insertIntoManagedObjectContext:[self managedObjectContext]];    student.name     = name;    student.age      = age;        return student;}

执行上述代码后运行结果为:
2014-07-31 09:13:40.424 StudyCoreData[16612:60b] 26 YouXianMing
2014-07-31 09:13:40.425 StudyCoreData[16612:60b] 27 QiuLiang

检查下数据库,此时只有两个属性哦:

 

然后我们给这个Student表新增加一个属性然后进行数据库的版本升级.

首先,我们先创建新的数据库表版本.

 

然后切换版本:

 

然后给Student新增加一个属性值

 

然后,我们来修改下源码试验测试结果:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{    NSLog(@"%@", NSHomeDirectory());        // 存储记录    [self saveContext];        // 设定要查询的实体    NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Student"];        // 取出查询结果    NSArray *students = [[self managedObjectContext] executeFetchRequest:fetch error:nil];    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {        Student *student = obj;        NSLog(@"%@ %@ %@", student.age, student.name, student.sex);    }];        return YES;}

运行后会崩溃,提示不兼容.

 

这个时候我们需要修改点东西:

找到以下地方.

将nil替换成如下的形式.

然后运行.

崩溃问题解决了,版本升级成功哦:)

解决问题出处:

http://stackoverflow.com/questions/8881453/the-model-used-to-open-the-store-is-incompatible-with-the-one-used-to-create-the

Deleting the app is sometimes not the case! Suggest, your app has already been published! You can‘t just add new entity to the data base and go ahead - you need to perform migration!

For those who doesn‘t want to dig into documentation and is searching for a quick fix:

  1. Open your .xcdatamodeld file
  2. click on Editor
  3. select Add model version...
  4. Add a new version of your model (the new group of datamodels added)
  5. select the main file, open file inspector (right-hand panel)
  6. and under Versioned core data model select your new version of data model for current data model
  7. THAT‘S NOT ALL ) You should perform so called "light migration".
  8. Go to your AppDelegate and find where the persistentStoreCoordinator is being created
  9. Find this line if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error])
  10. Replace nil options with @{NSMigratePersistentStoresAutomaticallyOption:@YES, NSInferMappingModelAutomaticallyOption:@YES} (actually provided in the commented code in that method)
  11. Here you go, have fun!

P.S. This only applies for lightweight migration. For your migration to qualify as a lightweight migration, your changes must be confined to this narrow band:

  • Add or remove a property (attribute or relationship).
  • Make a nonoptional property optional.
  • Make an optional attribute nonoptional, as long as you provide a default value.
  • Add or remove an entity.
  • Rename a property.
  • Rename an entity.


联系
我们