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85001
 Post subject: Entity manager throws NullPointer with LEFT JOIN FETCH
PostPosted: Sat Aug 02, 2008 3:53 pm 
Newbie

Joined: Wed Aug 29, 2007 3:45 pm
Posts: 4
I'm having a problem with entitymanager and LEFT JOIN FETCH Queries.

Hibernate throws a NullPointerException when calling Persistence.createEntityManagerFactory("fooPU"); (i use a named query, so exception occours when Hibernate is parsing this query).

Have anyone meet with such an error.

Hibernate version:

entitymanager 3.2.2.ga with dependencies fetched by maven

Mapping documents:

Code:
@NamedQueries({
   @NamedQuery(name = "foo",
         query= "SELECT f FROM FooEntity f LEFT JOIN FETCH f.baz WHERE f.id = :id")
})
@Entity
public class FooEntity {
   @Id
   Long id;

   @Basic(fetch = FetchType.LAZY)
   String baz;

   
   public Long getId() {
      return id;
   }


   public void setId(Long id) {
      this.id = id;
   }


   public String getBaz() {
      return baz;
   }


   public void setBaz(String baz) {
      this.baz = baz;
   }
   
}


If I change foo query to:

Code:
SELECT f FROM FooEntity f FETCH ALL PROPERTIES WHERE f.id = :id


everything works OK

Full stack trace of any exception that occurs:

Code:
Exception in thread "main" java.lang.NullPointerException
   at org.hibernate.hql.ast.HqlSqlWalker.createFromJoinElement(HqlSqlWalker.java:310)
   at org.hibernate.hql.antlr.HqlSqlBaseWalker.joinElement(HqlSqlBaseWalker.java:3275)
   at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromElement(HqlSqlBaseWalker.java:3067)
   at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromElementList(HqlSqlBaseWalker.java:2945)
   at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromClause(HqlSqlBaseWalker.java:688)
   at org.hibernate.hql.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:544)
   at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:281)
   at org.hibernate.hql.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:229)
   at org.hibernate.hql.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:228)
   at org.hibernate.hql.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:160)
   at org.hibernate.hql.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:111)
   at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:77)
   at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:56)
   at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:72)
   at org.hibernate.impl.SessionFactoryImpl.checkNamedQueries(SessionFactoryImpl.java:402)
   at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:352)
   at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1300)
   at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:859)
   at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:669)
   at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:126)
   at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:52)
   at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:34)
   at snippet.test.main(test.java:18)


Debug level Hibernate log excerpt:

I think thats the applicable part

DEBUG - Checking 1 named HQL queries
DEBUG - Checking named query: foo
DEBUG - unable to locate HQL query plan in cache; generating (SELECT f FROM FooEntity f LEFT JOIN FETCH f.baz WHERE f.id = :id)
DEBUG - parse() - HQL: SELECT f FROM snippet.FooEntity f LEFT JOIN FETCH f.baz WHERE f.id = :id
DEBUG - --- HQL AST ---
\-[QUERY] 'query'
+-[SELECT_FROM] 'SELECT_FROM'
| +-[FROM] 'FROM'
| | +-[RANGE] 'RANGE'
| | | +-[DOT] '.'
| | | | +-[IDENT] 'snippet'
| | | | \-[IDENT] 'FooEntity'
| | | \-[ALIAS] 'f'
| | \-[JOIN] 'JOIN'
| | +-[LEFT] 'LEFT'
| | +-[FETCH] 'FETCH'
| | \-[DOT] '.'
| | +-[IDENT] 'f'
| | \-[IDENT] 'baz'
| \-[SELECT] 'SELECT'
| \-[IDENT] 'f'
\-[WHERE] 'WHERE'
\-[EQ] '='
+-[DOT] '.'
| +-[IDENT] 'f'
| \-[IDENT] 'id'
\-[COLON] ':'
\-[IDENT] 'id'

DEBUG - throwQueryException() : no errors
DEBUG - select << begin [level=1, statement=select]
DEBUG - FromClause{level=1} : snippet.FooEntity (f) -> fooentity0_
DEBUG - Resolved : f -> fooentity0_.id
DEBUG - handling property dereference [snippet.FooEntity (f) -> baz (class)]
DEBUG - getDataType() : baz -> org.hibernate.type.StringType@e5355f
DEBUG - Resolved : f.baz -> fooentity0_.baz
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hardy.ferentschik
 Post subject:
PostPosted: Wed Aug 06, 2008 9:49 am 
Hibernate Team
Hibernate Team

Joined: Thu Apr 05, 2007 5:52 am
Posts: 1689
Location: Sweden
Hi,

in your example baz is a simple String property. LEFT JOIN FETCH really makes only sense when trying to retrieve associated entities. So in your case FETCH ALL PROPERTIES seems to be the right query.

--Hardy
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85001
 Post subject:
PostPosted: Wed Aug 06, 2008 10:05 am 
Newbie

Joined: Wed Aug 29, 2007 3:45 pm
Posts: 4
But what should I do to have baz fetched, withotut fetching everything else (lets suppose there are other fields that are expensive to fetch).
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hardy.ferentschik
 Post subject:
PostPosted: Wed Aug 06, 2008 11:29 am 
Hibernate Team
Hibernate Team

Joined: Thu Apr 05, 2007 5:52 am
Posts: 1689
Location: Sweden
Hi,

normally loading the basic properties of a class all at once is no problem. Are you trying to solve a particular problem? If you are only after a particular value of your entity projections might be what you are looking for. Of course you won't get entity objects back, but Object arrays.

--Hardy
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85001
 Post subject:
PostPosted: Wed Aug 06, 2008 11:44 am 
Newbie

Joined: Wed Aug 29, 2007 3:45 pm
Posts: 4
I have a class that has two big (@Lob) fields, and couple of others. Lobs are fetched lazily, and the others arn't. As far as I know fazy fetching of basic properties is legal. And I would like to have two queries: one gets all small properies and first Lob, second gets the second Lob, and rest of mandatory contents.

I use this in java SE enviorment and prefer to have my entity managers closed very fast, I could do:
Code:
try{
   FooEntity foo = entityManager.find();
   foo.getBaz(); //for side effect - prefetches contents of baz
}finally{
   entityManager.close();
}


But that would result in two queries sent to database. And I think there must be a way to prefetch basic property (just one; fetch all properties gets the whole lot) using EJB QL.

Well maybe there is some bad design in my database schema.
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hardy.ferentschik
 Post subject:
PostPosted: Wed Aug 06, 2008 12:26 pm 
Hibernate Team
Hibernate Team

Joined: Thu Apr 05, 2007 5:52 am
Posts: 1689
Location: Sweden
Hi,

lazy loading of properties is supported in Hibernate3, but requires bytecode instrumentation - http://www.hibernate.org/hib_docs/v3/reference/en/html_single/#performance-fetching-lazyproperties.

--Hardy
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85001
 Post subject:
PostPosted: Wed Aug 06, 2008 12:45 pm 
Newbie

Joined: Wed Aug 29, 2007 3:45 pm
Posts: 4
Thanks!

I'll look into it.
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