JPA Composite Key for one Table and a Primary Key for another Table - Possible?

Question

Is it possible to have both a composite key and a primary key in the same Domain Model (Entity Class) so that some tables (queries) are joined using the composite key and other tables (queries) are joined using the primary key?

I'm dealing with legacy applications and I have limited access to changing the underlying database. Some of our queries are expecting a single row result but are getting many rows because of flaws in our database design. We can fix this problem by introducing a composite key to one of our Domain Models but doing so will affect many (many) other components that rely on the original primary key.

From my understand of JPA and the reading I've done so far on this matter I do not think this is possible but I thought it would be worth a shot to reach out to others who may have had a similar problem.

Answer 1

The table has only one primary key , so you have no options to choose which primary key to use. Also, i can't understand why you going to have differences between database original model and JPA. Actually, getting single row instead of many rows is where clause's task.

You said some of your queries fails after adding composite pk, so may be you just made your composite pk in wrong way? Anyway, here is nice example or implementation composite pk, may be it will help you: Mapping ManyToMany with composite Primary key and Annotation:

Answer 2

Maybe you should give a different look at your problem.

1. If your queries are returning multiple and different rows, then you should be able to resolve this using a more specific WHERE clause;

2. If your queries are returning multiple and equal rows, you should try the DISTINCT clause inside your query, example:

SELECT DISTINCT e FROM br.com.stackoverflow.Entity e