title: How do I use JPA 2.1's CriteriaBuilder.function with MySQL's "GROUP_CONCAT"?
body: <p>I’m using JPA 2.1, Hibernate 4.3.6.Final, and MySQL 5.5.  I read JPA 2.1 supports invoking native DB functions, but I’m having trouble figuring out how to invoke MySQL's “GROUP_CONCAT.”  I have the following code …</p>
  
  <pre><code>final CriteriaBuilder builder = m_entityManager.getCriteriaBuilder();
  final CriteriaQuery criteria = StringUtils.equals(orderByCol, "organization") ? builder.createQuery(Tuple.class) : builder.createQuery(User.class);
  final Root&lt;User&gt; user = criteria.from(User.class);
      …
  final SetJoin&lt;User, Organization&gt; orgsJoin = orderByRoot.join(User_.organizations, JoinType.LEFT);
  final Expression groupConcatExpr = builder.function("GROUP_CONCAT", String.class, orgsJoin.get(Organization_.name));
   criteria.select(builder.tuple(user, groupConcatExpr))
                      .groupBy(user);
  …           
    orderByExpr = orgsJoin.get(Organization_.name);
    criteria.orderBy(orderByAscending == null || orderByAscending == true ? builder.asc(orderByExpr) : builder.desc(orderByExpr));
  </code></pre>
  
  <p>but I get the following exception …</p>
  
  <pre><code>java.lang.IllegalStateException: No data type for node: org.hibernate.hql.internal.ast.tree.MethodNode 
   \-[METHOD_CALL] MethodNode: 'function (GROUP_CONCAT)'
      +-[METHOD_NAME] IdentNode: 'GROUP_CONCAT' {originalText=GROUP_CONCAT}
      \-[EXPR_LIST] SqlNode: 'exprList'
         \-[DOT] DotNode: 'organizati2_.NAME' {propertyName=name,dereferenceType=PRIMITIVE,getPropertyPath=name,path=generatedAlias1.name,tableAlias=organizati2_,className=org.mainco.subco.organization.domain.Organization,classAlias=generatedAlias1}
        +-[ALIAS_REF] IdentNode: 'organizati2_.id' {alias=generatedAlias1, className=org.mainco.subco.organization.domain.Organization, tableAlias=organizati2_}
        \-[IDENT] IdentNode: 'name' {originalText=name}
  
      at org.hibernate.hql.internal.ast.tree.SelectClause.initializeExplicitSelectClause(SelectClause.java:174)
      at org.hibernate.hql.internal.ast.HqlSqlWalker.useSelectClause(HqlSqlWalker.java:924)
      at org.hibernate.hql.internal.ast.HqlSqlWalker.processQuery(HqlSqlWalker.java:692)
      at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:665)
      at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:301)
      at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:249)
      at org.hibernate.hql.internal.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:278)
      at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:206)
      at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:158)
      at org.hibernate.engine.query.spi.HQLQueryPlan.&lt;init&gt;(HQLQueryPlan.java:126)
      at org.hibernate.engine.query.spi.HQLQueryPlan.&lt;init&gt;(HQLQueryPlan.java:88)
      at org.hibernate.engine.query.spi.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:167)
      at org.hibernate.internal.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:301)
      at org.hibernate.internal.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:236)
      at org.hibernate.internal.SessionImpl.createQuery(SessionImpl.java:1800)
      at org.hibernate.jpa.spi.AbstractEntityManagerImpl.createQuery(AbstractEntityManagerImpl.java:568)
      at org.hibernate.jpa.criteria.CriteriaQueryImpl$1.buildCompiledQuery(CriteriaQueryImpl.java:336)
      at org.hibernate.jpa.criteria.compile.CriteriaCompiler.compile(CriteriaCompiler.java:147)
      at org.hibernate.jpa.spi.AbstractEntityManagerImpl.createQuery(AbstractEntityManagerImpl.java:736)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
      at java.lang.reflect.Method.invoke(Method.java:597)
      at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:240)
      at com.sun.proxy.$Proxy68.createQuery(Unknown Source)
      at org.mainco.subco.user.repo.UserDaoImpl.findUsers(UserDaoImpl.java:120)
      at org.mainco.subco.user.repo.UserDao2IT.testFindOrderByOrganizationAsc(UserDao2IT.java:624)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
      at java.lang.reflect.Method.invoke(Method.java:597)
      at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
      at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
      at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
      at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
      at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
      at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
      at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
      at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:231)
      at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
      at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
      at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
      at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
      at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
      at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
      at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
      at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
      at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
      at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:174)
      at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
      at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
      at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
      at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
      at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
      at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
  </code></pre>