JPA2.1 JPQL Query with multiple TREAT(...) operations in a JOIN

Question

I try to do a JPQL Query on the following Entity Graph: Derived1 and Derived2 are Subclasses of ReferencedEntity. Main Entity has a List of ReferencedEntity. Assume for now, that there is only one instance of Derived1 and Derived2 in the list of each MainEntity.

+--------------+
|  MainEntity  |
+--------------+                    +------------------+
|  list        | --- OneToMany ---> | ReferencedEntity |
+--------------+                    +------------------+
                                    | String a1        |
                                    +------------------+
                                              ^
                                              |
                                  +-----------+-----------+
                                  |                       |
                          +--------------+         +--------------+
                          |   Derived1   |         |   Derived2   |
                          +--------------+         +--------------+
                          |   String d1  |         |   String d2  |
                          +--------------+         +--------------+

Now I want to Group MainEntities by the d1 and d2 Values they contain in their List. Therefore I write the following JPQL Query:

SELECT COUNT(m) FROM MainEntity m JOIN TREAT(m.list AS Derived1) der1, TREAT(m.list AS Derived2) der2 GROUP BY der1.d1, der2.d2

I think this should work but I get:

Caused by: Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.JPQLException
Exception Description: Syntax error parsing [SELECT COUNT(m) from MainEntity m JOIN TREAT(m.list AS Derived1) der1, TREAT(m.list AS Derived2) der2 GROUP BY der1.d1, der2.d2]. 
[83, 84] The FROM clause has 'TREAT(m.list' and 'AS Derived2' that are not separated by a comma.
[83, 83] The right parenthesis is missing from the sub-expression.
[77, 83] The identification variable 'm.list' is not following the rules for a Java identifier.
[84, 84] A "root object" must be specified.
[95, 127] The query contains a malformed ending.
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.buildException(HermesParser.java:155)
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.validate(HermesParser.java:334)
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.populateQueryImp(HermesParser.java:278)
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.buildQuery(HermesParser.java:163)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.buildEJBQLDatabaseQuery(EJBQueryImpl.java:142)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.buildEJBQLDatabaseQuery(EJBQueryImpl.java:116)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.<init>(EJBQueryImpl.java:102)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.<init>(EJBQueryImpl.java:86)
        at org.eclipse.persistence.internal.jpa.EntityManagerImpl.createQuery(EntityManagerImpl.java:1583)
        ... 2 more
Java Result: 1

Just for testing purposes I tried a different join:

SELECT COUNT(m) FROM MainEntity m JOIN TREAT(m.list AS Derived1) der1, m.list refd GROUP BY der1.d1, refd.a1

This one works and delivers a result.

Then i tried a third query and just changed the order of the join:

SELECT COUNT(m) FROM MainEntity m JOIN m.list refd, TREAT(m.list AS Derived1) der1 GROUP BY der1.d1, refd.a1

This leads to exactly the same Exception (but this time for Derived1).

Caused by: Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.JPQLException
Exception Description: Syntax error parsing [SELECT COUNT(m) from MainEntity m JOIN m.list refd, TREAT(m.list AS Derived1) der1 GROUP BY der1.d1, refd.a1]. 
[64, 65] The FROM clause has 'TREAT(m.list' and 'AS Derived1' that are not separated by a comma.
[64, 64] The right parenthesis is missing from the sub-expression.
[58, 64] The identification variable 'm.list' is not following the rules for a Java identifier.
[65, 65] A "root object" must be specified.
[76, 108] The query contains a malformed ending.
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.buildException(HermesParser.java:155)
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.validate(HermesParser.java:334)
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.populateQueryImp(HermesParser.java:278)
        at org.eclipse.persistence.internal.jpa.jpql.HermesParser.buildQuery(HermesParser.java:163)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.buildEJBQLDatabaseQuery(EJBQueryImpl.java:142)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.buildEJBQLDatabaseQuery(EJBQueryImpl.java:116)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.<init>(EJBQueryImpl.java:102)
        at org.eclipse.persistence.internal.jpa.EJBQueryImpl.<init>(EJBQueryImpl.java:86)
        at org.eclipse.persistence.internal.jpa.EntityManagerImpl.createQuery(EntityManagerImpl.java:1583)
        ... 2 more
Java Result: 1

To me it looks like there might be a bug in EclipseLink, or am I trying something thats forbidden?

Answer 1

According to the specification, the correct syntax should be:

... JOIN TREAT(m.list AS Derived1) der1 JOIN TREAT(m.list AS Derived2) der2 ...

without any commas.