as topic, I just want create new Entity(table) in sqlite ,

my code as follows:

+(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]];
//@step
NSArray *properties =   [CoreDataHelper CreateAttributes:attributes];
[entityDef setProperties:properties];

[entityDef release];

return TRUE;

}

but it throw errors:

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 ....

that seem show the model is read only.....

anyone can help on this problem? thanks