Parent Child Context Confusion & Concurrency issues

Question

Am having few doubts with parent child context set-up and how the data behaves. Can anyone please suggest a link where i can find proper explanation on how they work.

Few Points & Observation

1. Parent context acts as store for child context :- But the changes in the parent are not reflected in the child.

Question 1: If parent context acts as store for child context then why does the changes in the parent are not reflected in the child context, while the child fetches them.

Observations :

1. Insert in parent :- Child fetch requests get those objects.
2. Update/delete a object in parent :- Then the fetch request do not get the updated object instead it provides us with the object in child context, so if we need the updated object we have to either reset the context but then we will lose all the changes in the child context or refresh the object.

Question 2: Child overwrites parent context values. So if the user has modified something in parent context and child has also modified the same thing then the updates of user will be lost. This is not much problem until relationships are involved.

Say there is one to many relationship between entity A,B (A->>B).

Parent Context : Inserts a new child to entity A say Child-1.

Child Context : Deletes both entity A and all its child.

So now when the child saves to parent context, then it deletes entity A and its old child, the newly inserted child-1 remains in the context with null referencing parent.

How can i resolve this issue?

Answer 1

Question 1 Because you have already fetched the data, if you want to force a fetch as you said you should either reset the context or refresh the object.

Question 2 You can try to use cascade delete if you want to always delete entities B when the parent entity A is deleted.