I've got a document-based Core Data application which works as is. I would like
to add support for a global persistent store to hold a library of items.
I've read most of the relevant docs, and understand that I should use
configurations in the managed object models. I've defined two configurations:
"DocumentConfiguration" and "LibraryConfiguration". The entities in the
document configuration are only in the document configuration, and the entities
in the library configuration are only in the library configuration -- i.e., no
overlap.
The docs then say "You then use this model when you create a coordinator". But
I don't actually create my own persistent store coordinator since I'm using the
default NSPersistentDocument coordinator.
A few questions on how best to proceed and help clear up any misunderstandings
I might have:
1. Would I obtain the NSPersistentStoreCoordinator in the NSPersistentDocument
and then add a new persistent store to it along the lines of:
NSPersistentStoreCoordinator * coordinator = [[myDocument
managedObjectContext] persistentStoreCoordinator];
[coordinator addPersistentStoreWithType:NSXMLStoreType
configuration:@"LibraryConfiguration"
URL:url
options:nil
error:&error];
?
I'm thinking that this may be a problem because I haven't provided the other
configuration definition ("DocumentConfiguration") in the
NSPersistentDocument's persistent store coordinator as I'm using the default
provided by NSPersistentDocument. I'm guessing it would probably use nil when
the time came to save the document. And if so, would this be a problem? I.e.,
how would the coordinator know which persistent store to save an entity with a
given configuration definition if the same configurations are not defined for
all the persistent stores (in this case two)? Am I able to set the
configuration (to "DocumentConfiguration") of the NSPersistentDocument's
persistent store before it has been created/saved? From the
NSPersistentDocument docs:
"Saving a new document adds a store of the default type with the chosen URL and
invokes save: on the context. For an existing document, a save just invokes
save: on the context."
2. Would it be better to create my own NSPersistentStoreCoordinator and
NSManagedObjectContext instances, adding the two persistent stores with
configurations defined, and then make the NSPersistentDocument use these
NSPersistentStoreCoordinator and NSManagedObjectContext instances, and free the
old ones? If so, how would I specify the url for the NSPersistentDocument for
the addPersistentStoreWithType:... method? It seems this URL is only known once
the untitled document has been saved. (Testing this, there does not appear to
be any temporary persistent store (via method persistentStores on the
persistent store coordinator) until the document is saved for the first time).
3. Or would it be better to leave NSPersistentDocument alone, and create my own
NSPersistentStoreCoordinator instance that I use exclusively for the persistent
library store and managed library object model? The docs say that multiple
instances of NSPersistentStoreCoordinator should be used in multithreaded Core
Data applications, but I don't require multithreaded Core Data support. Is it
desirable to have two instances of NSPersistentStoreCoordinator -- one for the
library and one for documents (intuition says that this not necessary and
probably not the correct approach)?
Any suggestions?
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