CODEWITHSUNDEEP
core-datamany-to-manyrelationship
Thomas Albert
Thomas Albert

Reputation: 277

Delete rules for a Core Data many-to-many relationship

I know there are a lot of questions about the delete rules of Core Data relationships, but I didn't find an answer to my "problem".

In my Core Data Model, I have a many-to-many relationship between the CDMTransaction and CDMTransactionTag entities (CDMTransaction.tags <<->> CDMTransactionTag.transactions). Each transaction can be linked to zero, one or more tag, and then every tag can be linked to one or more transaction (or zero, but this doesn't make sense to keep it, and this is what I'm working on).

So when I delete a tag (will a "Nullify" delete rule), it is removed from the transactions that had this tag. This is OK. But what I would like to do, is when I delete a transaction and its linked tag(s) remained unused (CDMTransactionTag.transactions.@count == 0), this/these tag(s) should be also deleted.

Can I set a "Cascade" rule for the CDMTransaction entity? It would delete all its linked tags, even if they are still linked to other transactions, no?

Am I forced to do that programmatically?

Thanks!

Edit: in fact, I just would like to delete the CDMTransactionTag instances when their .transactions.@count == 0 (so it shouldn't be checked only when I delete some transactions, but also when I change the tags of a transaction).

Upvotes: 1

Views: 280

Answers (1)

Ron Liu
Ron Liu

Reputation: 188

Don't know if you are still pursuing to a solution within your desired scope.

I'm dealing with similar issues and would like to share my findings so far:

  1. Among the delete rules, only cascade will delete the object(s) (e.g. in your question: your *Tag entity instance(s)) at the relationship (1st) destination,

  2. it does delete the destination objects even if they are "still linked to other transactions" unless...,

  3. unless the "linked to other transactions" is a relationship(2nd) with delete rule of deny,

  4. because only deny rule can prevent source object to be deleted when there is at least one object at the relationship(2nd) destination among the rules; and,

  5. the delete rules are to specify what should happen if AN ATTEMPT is made to delete the source object, (i.e. the moment just right before the possible source object deletion occurs).

I have not yet tested the above design for the similar issues but I will try and post the result later if I may see some ongoing activities to the post.

Upvotes: 1

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