问题
I doubt it but still want to confirm if these limitations are still there or not when using JPA with Cloud SQL.
Unsupported Features of JPA 1.0
The following features of the JPA interface are not supported by the App Engine implementation:
- Owned many-to-many relationships, and unowned relationships. You can implement unowned relationships using explicit Key values, though type checking is not enforced in the API.
- "Join" queries. You cannot use a field of a child entity in a filter when performing a query on the parent kind. Note that you can test the parent's relationship field directly in a query using a key.
- Aggregation queries (group by, having, sum, avg, max, min).
- Polymorphic queries. You cannot perform a query of a class to get instances of a subclass. Each class is represented by a separate entity kind in the datastore.
回答1:
Those limitations apply to JPA 1.0 for Datastore. Cloud SQL is using native MySQL driver in App Engine so JPA should work properly (there are examples for EclipseLink, DataNucleus and Hibernate).
来源：https://stackoverflow.com/questions/26832235/are-these-limitations-still-there-when-using-jpa-with-cloud-sql