I am a little fuzzy about Core Data Relationships deletion rules. So if someone could help me answer a few questions about them.
I have Entities A and B. A has a to-Many relationship with B, and B has a to-One relationship with A.
A<--->>B
Now, if I set the delete rule at A to Cascade, I understand it will delete all the Bs related to it. But if I set it to Nullify, will it set the Bs to NIL or just the Foreign Key to Nil?
And I looked everywhere about the relationship from B to A, should I set it to Nullify? Will that just Nullate the "B Object" at A? Or will it Nullify all the Bs associated with A? What about Cascade? Will it delete all the Bs associated with A, or just the particular B?
Or do I just use "No Action" on the relation from B to A so that when I delete B, no change will happen to A, but the reference to B won't exist?
I am PRETTY confused with these, so excuse my questions.
Thanks.
A delete rule defines what happens when the record that owns the relationship is deleted. A delete rule defines what happens when the record that owns the relationship is deleted. Select the notes relationship of the Category entity and open the Data Model Inspector on the right.
Setting the Delete Rule to Delete guarantees that when a record of the main Entity is deleted, all the associated records in the related Entities are also deleted.
Table views have a built-in swipe to delete mechanic that we can draw upon to let users delete commits in our app. Helpfully, managed object context has a matching delete() method that will delete any object regardless of its type or location in the object graph.
Overview. After you create a data model file as described in Creating a Core Data Model, set up the classes that collaboratively support your app's model layer. These classes are referred to collectively as the Core Data stack.
If you set the delete rule to "nullify" and delete the A object, then the references to that object in the Bs will be removed. The inverse works the same way. If you have cascade and delete B then it will remove the A that B pointed to. It will then follow the delete rule from A to the remaining Bs (either cascade or nullify).
The rules you set really depend on your data model. If A were a customer and B were their orders then you could set the A->B rule to deny (prevent A from being deleted if it the customer has orders) or cascade (delete the orders when the customer is deleted). The B->A rule would probably be "nullify". If an order is deleted simply remove the reference to the order from the customer.
The relationship delete rules are described in the Apple Core Data Programming Guide
Let be assume we have database with table person and work. Single person can have many tasks to do.
Sample data and ER relationship
"The operation couldn’t be completed. (Cocoa error 1600.)"
on saving the context. Now to delete the Iron Man person, we need to delete all his associated tasks and then we could able to delete the Person.If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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