JPA @OneToMany -> Parent - Child Reference (Foreign Key)

Question

i have a Question about referencing ParentEntities from Child Entites ir If i have something like this:

Parent.java:

@Entity(name ="Parent")
         


        

Answer 1

We ran into a problem while persisting a simple object graph like the one shown above. Running in H2 everything would work, but when we ran against MySQL the "paren_id" in the child table (defined in the @JoinColumn annotation) wasn't getting populated with the generated id of the parent - even though it was set as a non-null column with a foreign key constraint in the DB.

We'd get an exception like this:

org.hibernate.exception.GenericJDBCException: Field 'paren_id' doesn't have a default value

For anyone else who might run into this, what we eventually found was that we had to another attribute to the @JoinColumn to get it to work:

@JoinColumn(name="paren_id", nullable=false)