Toplink Caching issue

Question

I have three Entities say C1 , P1 and card. Relation between these
entities are like this
P1 to Card ( one - one mapping )
C1 to Card ( one - many mapping )
I have three usecases. Usecase 1 uses the mail Entity C1. It will
create one record using C1. ( keep in mind that there will not be any data for entity card at that time ).
Second usecase , Usecase 2 , uses Entity P1 and creates data in P1 as
well as Card.
Third usecase will again take C1 and try to get the card data which
were inserted through P1.
But unfortunately , it is coming as null ... But if I restart the server and access the third usecase then I'm getting all the card data from C1 Entity which were saved through P1 Entity .
To summarise my finding , issue is with Toplink caching. When i
accessed the first usecase, C1 is cached. In the second usecase , I updated Entity card using P1. When i accessed the third usecase , toplink is returing the cached entity. Toplink is not able to identify whether related entity got changed or not....
Workaround is not to use cache for C1 entity. It is working but it will
not be the correct solution.
any one faced this issue in Toplink ?
Correct me if my findings are not correct...

Answer 1

Hello,
Its not that the cache isn't working, its that you are updating relationships in the database but not in the cache. Take the case of a 1:M from B->C used in a previous response. It looks like the foreign key used in this relationship (in the C table) is mapped to the C object either as a direct to field mapping, or through a 1:1 to the A object. When you change this so that it now somehow points to the B object, you haven't updated the B object to include the C in its collection. Because B has a 1:M mapping collection of Cs, when you next get that B object from the cache, its collection will not contain the newly referenced C (assuming indirection is not used or has been previously triggered). This is a result of you mapping the 1:M in the first place - since it is storing the collection in the object.
If you are going to make changes that affect relationships and yet not update the relationships directly I would suggest either:
A) refreshing affected objects from the database when done. In this case, refreshing the B object will result in TopLink requerying the B->C relation and picking up any changes (depending on your refresh options on the B descriptor though - please check the docs if you need more info).
B) Not mapping these relationships. Instead, when you need to find C objects referenced from B, query for them.
Both options are less efficient as they cause more hits to the database. This is why it would be preferred if you updated the relationships when you change fields that affect those relationships, but it is up to you to decide which will work best for your application.
Please note that the cache is working, in fact the situation you are seeing is due to it working. I am not sure of how your situation would work with DAO as you mentioned in a previous post, but it sounds like it would always hit the database. This situation is a result of you making changes in the database but not changing the object model to reflect those changes, proving that the cache is indeed working. While you mention that some objects are not in your use case, they are in the database but just not mapped in TopLink. In the case of a 1:M mapping, the database shows a 1:1 back relationship that you have not mapped in your object model. So this would be more a case of your object model not matching your database model, and not being taken into account in your use cases.
Best Regards,
Chris