我想在sqlite中创建一个新的实体(表).我的代码如下：
+(BOOL)CreateDataSet:(NSManagedobjectModel *) model
attributes:(NSDictionary*)attributes
entityName:(Nsstring*) entityName
{
NSEntityDescription *entityDef = [[NSEntityDescription alloc] init];
[entityDef setName:entityName];
[entityDef setManagedobjectClassName:entityName];
[model setEntities:[NSArray arrayWithObject:entityDef]];
NSArray *properties = [CoreDataHelper CreateAttributes:attributes];
[entityDef setProperties:properties];
[entityDef release];
return TRUE;
}
但它会引发错误：
Terminating app due to uncaught exception 'NSInternalInconsistencyException',reason: 'Can't modify an immutable model.'
*** Call stack at first throw:
(
0 CoreFoundation 0x01c5abe9 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x01daf5c2 objc_exception_throw + 47
2 CoreData 0x0152634a -[NSManagedobjectModel(_NSInternalMethods) _throwIfNotEditable] + 106
3 CoreData 0x01526904 -[NSManagedobjectModel setEntities:] + 36
....
这似乎表明该模型是只读的.
解决方法
From the documentation:(重点是我的)
Managed object models are editable
until they are used by an object graph
manager (a managed object context or a
persistent store coordinator). This
allows you to create or modify them
dynamically. However,once a model is
being used,it must not be changed.
This is enforced at runtime—when the
object manager first fetches data
using a model,the whole of that model
becomes uneditable. Any attempt to
mutate a model or any of its
sub-objects after that point causes an
exception to be thrown. If you need to modify a model that is in use,create a copy,modify the copy, and then discard the objects with the old model.