在单个查询中使用FK更新现有的JPA子实体

Question

I have a parent/child one-to-many unidirectional relation. Both the parent and the child POJOs use custom Insert-on-duplicate-update insert queries specified via @SQLInsert annotation.

Parent/child pair is inserted via cascading - everything works fine and the entity manager is closed. Then I create a new entity manager and try to insert the same parent/child pair, but with updated values (same primary keys, but some of the other fields are changed).

The parent's Insert-on-duplicate-update works just fine and the values are updated. In the child table however we end up with 2 entries, one with the old values and NULL parent_id foreign key, and one with the new values and correctly set FK.

I looked at the queries generated by Hibernate and found out the following:

• The child row is inserted with the foreign key set to NULL
• Then an update query is ran that sets the parent_id for the given child id
• Another update is ran that sets the parent_id to NULL, I'm assuming for the child id of the first row
• A third update query is ran that sets the parent_id

Is there a way for cascading insert to insert the child row and set the FK in the same query, thus eliminating the need for running a separate update query?

Answer 1

The question was answered as a part of a different question of mine: JPA insert parent/child results in MySQLIntegrityConstraintViolationException

Basically, you have to set nullable = false in the @JoinColumn that specifies creates the parent/child relation.

There still seems to be an update query running for some reason but the complete record is being inserted with the insert statement.

Answer 2

The accepted answer did not solve my problem.

Adding updatable=false to the parent entity solved it. JPA does not execute the update query. However, I have no clue why that's the case and in fact, I don't think what I am doing is correct because it means I cannot update the child table later on if I have to.