How to create a JPA query with LEFT OUTER JOIN

Question

I am starting to learn JPA  and have implemented an example with JPA query  based on the following native SQL that I tested in SQL Server   SELECT f StudentID  f Name  f Age  f Class1  f Class2  FROM Student f      LEFT OUTER JOIN ClassTbl s ON s ClassID   f Class1 OR s ClassID   f Class2 WHERE s ClassName    abc    From the above SQL I have constructed the following JPQL query   SELECT f FROM Student f LEFT JOIN f Class1 s    As you can see  I still lack the condition OR s ClassID   f Class2 from my original query  My question is  how can I put it into my JPQL

User · Answer

If you have entities A and B without any relation between them and there is strictly 0 or 1 B for each A, you could do:

select a, (select b from B b where b.joinProperty = a.joinProperty) from A a

This would give you an Object[]{a,b} for a single result or List<Object[]{a,b}> for multiple results.

User · Answer

Write this    SELECT f from Student f LEFT JOIN f classTbls s WHERE s ClassName    abc    Because your Student entity has One To Many relationship with ClassTbl entity

User · Answer

Normally the ON clause comes from the mapping s join columns  but the JPA 2 1 draft allows for additional conditions in a new ON clause   See   http   wiki eclipse org EclipseLink UserGuide JPA Basic JPA Development Querying JPQL ON

[java] How to create a JPA query with LEFT OUTER JOIN

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