尝试在Core Data中执行大量迁移后保存数据 [英] Trying to save data after doing heavy weight migration in Core Data
问题描述
我正在开发一个需要大量迁移的iOS应用程序。我做的是将我的旧数据模型中的类型为Integer64的实体的属性类型转换为新数据模型中的String类型。因为我正在改变属性的类型，这需要大量的迁移。现在，转换是工作正常，但不幸的是，我有麻烦保存新的实体后，它转换后，这就是为什么当我在迁移后启动我的应用程序，我无法查看使用输入的数据旧数据模型。这里是我使用的NSEntityMigrationPolicy的子类：
- （BOOL）createDestinationInstancesForSourceInstance：（NSManagedObject *）sInstance entityMapping :( NSEntityMapping *）映射管理器：（NSMigrationManager *）管理器错误：（NSError * __ autoreleasing *）错误{
NSManagedObject * newObject;
NSEntityDescription * sourceInstanceEntity = [sInstance entity];
NSManagedObjectContext * destMOC = [manager destinationContext];
//正确的实体？只是为了确保
if（[[sourceInstanceEntity name] isEqualToString：@MyEntity]）{
newObject = [NSEntityDescription insertNewObjectForEntityForName：@MyEntityinManagedObjectContext：destMOC];
//获取属性
NSDictionary * keyValDict = [sInstance committedValuesForKeys：nil];
NSDictionary * allAttributes = [[sInstance entity] attributesByName];
//在属性上循环
for（NSString * key in allAttributes）{
//获取键和值
id value = [sInstance valueForKey：key] ;
if（[key isEqualToString：@myAttribute]）{
//这里检索旧值
NSNumber * oldValue = [keyValDict objectForKey：key];
//这里根据需要进行转换
NSString * newValue = [oldValue stringValue];
//然后存储新值
[newObject setValue：newValue forKey：key];
} else {
//不需要修改值，复制到
[newObject setValue：value forKey：key];
}
}
[manager associateSourceInstance：sInstance withDestinationInstance：newObject forEntityMapping：mapping];
[destMOC save：error];
}
return YES;
}
- （BOOL）createRelationshipsForDestinationInstance：（NSManagedObject *）dInstance entityMapping：（NSEntityMapping *）mapping manager：（NSMigrationManager *）manager error：（NSError * __ autoreleasing *）error {
return YES;
}
我试图尽可能彻底，也走过了迁移过程，但不幸的是，我不知道为什么我转换的实体没有保存在新的数据模型。我想指出一些可能是原因：
我正在转换/迁移的实体与4个其他实体有4个一对一的关系：一个关系具有逆，并且这些关系中的三个不具有逆。我知道有一个没有逆的关系是不推荐的，但这是如何设计原始的数据模型，不幸的是我没有什么能做的。但是，这些关系不会以任何方式从我的旧数据模型改变到新的数据模型。我的方法：
- （BOOL）createRelationshipsForDestinationInstance：（NSManagedObject *）dInstance entityMapping :( NSEntityMapping *）映射管理器： *）manager error：（NSError * __ autoreleasing *）error {
return YES;
}
现在必须更改以适应此，从而允许我保存我的数据，或者我可以单独使用这个方法，仍然保存数据我只是改变方法：
- （BOOL） createDestinationInstancesForSourceInstance：（NSManagedObject *）sInstance entityMapping：（NSEntityMapping *）mapping manager：（NSMigrationManager *）manager error：（NSError * __ autoreleasing *）error {...}
仍然保持现有的关系，因为它们是完整的？
我希望我的问题有意义。 >
感谢所有回复者。
改变所有关系类型以在原始模型中具有逆关系，并且在新模型中保持相同的结构。当我使用上面的代码，一切都很好。
感谢所有考虑过这个问题的人。
I am working on an iOS application that requires heavy weight migration. What I am doing is converting the attribute type of an Entity in my old Data Model which is of type Integer64, to a type of String in the new Data Model. Because I am changing the type of the attribute, this requires heavy weight migration. Now, the conversion is working fine, but unfortunately I am having trouble saving the new Entity after it has been converted, which is why when I launch my application after doing the migration, I'm unable to view the data that was entered using the old Data Model. Here is the subclass of NSEntityMigrationPolicy that I am using:
- (BOOL)createDestinationInstancesForSourceInstance:(NSManagedObject *)sInstance entityMapping:(NSEntityMapping *)mapping manager:(NSMigrationManager *)manager error:(NSError *__autoreleasing *)error {
NSManagedObject *newObject;
NSEntityDescription *sourceInstanceEntity = [sInstance entity];
NSManagedObjectContext *destMOC = [manager destinationContext];
//correct entity? just to be sure
if ([[sourceInstanceEntity name] isEqualToString:@"MyEntity"]) {
newObject = [NSEntityDescription insertNewObjectForEntityForName:@"MyEntity" inManagedObjectContext:destMOC];
//obtain the attributes
NSDictionary *keyValDict = [sInstance committedValuesForKeys:nil];
NSDictionary *allAttributes = [[sInstance entity] attributesByName];
//loop over the attributes
for (NSString *key in allAttributes) {
//get key and value
id value = [sInstance valueForKey:key];
if ([key isEqualToString:@"myAttribute"]) {
//here retrieve old value
NSNumber *oldValue = [keyValDict objectForKey:key];
//here do conversion as needed
NSString *newValue = [oldValue stringValue];
//then store new value
[newObject setValue:newValue forKey:key];
} else {
//no need to modify the value, Copy it across
[newObject setValue:value forKey:key];
}
}
[manager associateSourceInstance:sInstance withDestinationInstance:newObject forEntityMapping:mapping];
[destMOC save:error];
}
return YES;
}
- (BOOL) createRelationshipsForDestinationInstance:(NSManagedObject *)dInstance entityMapping:(NSEntityMapping *)mapping manager:(NSMigrationManager *)manager error:(NSError *__autoreleasing *)error {
return YES;
}
I've tried to be as thorough as I can, and I've also stepped through the migration process, but unfortunately I can't figure out why the Entity that I'm converting is not being saved in the new Data Model. I do want to point out something that could possibly be the reason:
This entity that I am converting/migrating has 4 one-to-one relationships with 4 other entities: one relationship has an inverse, and three of these relationships do NOT have an inverse. I know having a relationship without an inverse is not recommended, but this is how the original Data Model was designed, and unfortunately there is nothing I can do about it. However, these relationships do NOT change in any way from my old Data Model to the new Data Model. Does my method:
- (BOOL) createRelationshipsForDestinationInstance:(NSManagedObject *)dInstance entityMapping:(NSEntityMapping *)mapping manager:(NSMigrationManager *)manager error:(NSError *__autoreleasing *)error {
return YES;
}
have to change now to accommodate this, and thus allowing me to save my data, or can I leave this method alone, and still save the data my simply making changes to the method:
- (BOOL)createDestinationInstancesForSourceInstance:(NSManagedObject *)sInstance entityMapping:(NSEntityMapping *)mapping manager:(NSMigrationManager *)manager error:(NSError *__autoreleasing *)error {...}
and still keep the existing relationships as they were intact?
I hope my question makes sense.
Thanks in advance to all who reply.
I solved this problem by changing all of the relationship types to have inverse relationships in the original model, and kept this same structure in the new model. When I used my above code as is, everything worked fine.
Thanks to all who considered this problem.
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