re: Core Data: Cross-Model Relationships
re: Core Data: Cross-Model Relationships
- Subject: re: Core Data: Cross-Model Relationships
- From: Ben Trumbull <email@hidden>
- Date: Wed, 14 Nov 2007 16:46:31 -0800
Kai,
So far, so easy: +[NSManagedObjectModel modelByMergingModels:] will
merge my sub-models nicely. But I need some cross-sub-model
relationships. My idea is to create these relationships
programmatically after the sub-models have been loaded and merged
into one model.
Questions:
- Is this feasible and a good idea?
- Does my whole consideration make sense?
- Is there a better/easier way to achieve what I want?
On the whole what you propose makes sense. There is one delicate
consideration. When you open a store file, the model you use must
match exactly the model used to create the store. No more, no less.
So two points come up. Any programmatic alterations to a model must
be maintained. If you add some code, and then save some files, you
can't change your mind later about what programmatic alterations to
make without performing a schema migration.
Secondly, the sub-stores and sub-models cannot at runtime actively
use a subset of the primary model. They either need to exactly use
the primary model, or have their own NSPersistentStoreCoordinator
with their own precise model.
Or put another way, Core Data doesn't support dynamic plugins to the
model without either a different coordinator, a schema migration
step, or both.
--
-Ben
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