Add support for composite user types in Hibernate

Currently it is not possible to query composite properties of an entity. However, Hibernate does support such constructions through the CompositeUserType interface and @Type annotation. In our implementation of Java Money using Jadira we encountered such a composite type; Money, which consists of the properties amount and currency. We would like to be able to query it correctly using Blaze.

Currently, attempting to query a composite type throws

java.lang.IllegalArgumentException: The join path [product.price.amount] has a non joinable part [price.amount]

[jwgmeligmeyling]

I recently started working on this issue (https://github.com/jwgmeligmeyling/blaze-persistence/commit/6c2ca771c34c5c3f43cb903921d8f861906a1f03). Basically we need to treat Composite types as embeddables. Making this change in our metamodel is relatively easy. However, a lot of code still uses the plain JPA metamodel. In order to support composite user types fully, we need to change these occurrences of JPA metamodel access to that they use BP’s internal metamodel instead. This is a change we’re willing to make, because it’s not only required for dereferencing composite user types but its also relevant for dereferencing JSON properties.

[beikov]

It is actually a separate project since the beginning. The only reason for needing it as separate project is for modules like entity-view-impl etc. which do parsing at boot time, but I think it should be fine to instead depend on core-impl. I don’t expect a different implementation of Blaze-Persistence anyway 😆