JPA/Hibernate Join On Constant Value

Question

I am trying to join to different entities from the same table using a constant value in the join statement. In SQL, I would do something like this...

SELECT         


        

Answer 1

If you don't mind using Hibernate-specific annotations you could try with the @WhereJoinTable annotation, e.g.:

@OneToOne(mappedBy = "owner", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@JoinColumn(name = "ID", referencedColumnName = "ID")
@WhereJoinTable(clause = "TYPE = 'A'")
private TypeA inspectionSnapshot;

Note that the clause attribute must contain SQL, not JPQL, so you need to use the database column name instead of the JPA entity field name.

Answer 2

Try to specify a constant as the value of the formula

@JoinColumnsOrFormulas({
@JoinColumnOrFormula(formula=@JoinFormula(value="'A'", referencedColumnName="type")),
@JoinColumnOrFormula(column = @JoinColumn("id", referencedColumnName="id"))
})
private TypeA inspectionSnapshot;

Answer 3

You're looking at non-standard joins. Here's the documentation for treating such a case:

http://docs.oracle.com/cd/E13189_01/kodo/docs40/full/html/ref_guide_mapping_notes_nonstdjoins.html

Hope it helps!