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I wonder if there is any migration guide from JPAContainer 1.2.1 to 2.0.0? I did not found one.
I got massive problems converting the old Filter API to the new one. As i understand there is no low level filtering anymore, instead we have to use the high level Container filtering api? If thats true i'm worried about the performance impact.
Don't know what you mean by low level, but filtering is still done at DB level with JPAContainer. Instead of the previous JPAContainer specific API you can now just use the standard Vaadin Filterable Filters. You just have to note that you cannot write own custom versions of them as JPAContainer needs to know how to convert them to queries.
Also there is still the Filters class available that should help in migration. At a time it was already removed altogether, but we added it back when migrating one of our internal projects.
If you need some more complex queries, you should look at QueryModifierDelegate. With it you can modify the JPA 2 Criteria query built by JPAContainer.