many-to-many association table persistence problem

bdimmick · **Posted:** Thu Sep 02, 2004 2:49 pm

Anyone know why the many-to-many mappings below won't persist data into the association table (a2b)? All of the data gets persisted except the associtations, which is unfortunate since that's what I am most interested in. Nothing unusual in the logs and show_sql shows a query to 'a2b' but not an insert of any data.

Hibernate version:2.1.6

Mapping documents:

Alpha.hbm.xml

Code:

<hibernate-mapping package="com.rhoworld.tests.sharedcollection">
   <class name="Alpha" table="alpha">
      <id name="id" column="id" type="java.lang.Integer">
         <generator class="native"/>
      </id>
      <set name="betas" inverse="false" table="a2b" lazy="true" cascade="all-delete-orphan">
               <key column="alpha_id"/>
               <many-to-many column="beta_id" class="Beta"/>
        </set>      
   </class>
</hibernate-mapping>

Beta.hbm.xml

Code:

<hibernate-mapping package="com.rhoworld.tests.sharedcollection">
   <class name="Beta" table="beta">
      <id name="id" column="id" type="java.lang.Integer">
         <generator class="native"/>
      </id>
      <set name="alphas" inverse="true" table="a2b" lazy="true">
               <key column="beta_id"/>
               <many-to-many column="alpha_id" class="Alpha"/>
        </set>
   </class>

</hibernate-mapping>

Code between sessionFactory.openSession() and session.close():

Code:

      Configuration config=new Configuration();
      config.addClass(Alpha.class);
      config.addClass(Beta.class);
      SessionFactory factory=config.buildSessionFactory();
      Session session=factory.openSession();
      Alpha a1=new Alpha();
      Alpha a2=new Alpha();
      Beta b1=new Beta();
      Beta b2=new Beta();
      Beta b3=new Beta();
      session.saveOrUpdate(b1);
      session.saveOrUpdate(b2);
      session.saveOrUpdate(b3);
      session.saveOrUpdate(a1);
      session.saveOrUpdate(a2);
      Integer a1key=a1.getId();
      Integer a2key=a2.getId();
      Integer b1key=b1.getId();
      Integer b2key=b2.getId();
      Integer b3key=b3.getId();
      a1=null;
      a2=null;
      b1=null;
      b2=null;
      b3=null;
      System.gc();
      session.disconnect();
      session=factory.openSession();
      a1=(Alpha)session.load(Alpha.class, a1key);
      a2=(Alpha)session.load(Alpha.class, a2key);      
      b1=(Beta)session.load(Beta.class, b1key);
      b2=(Beta)session.load(Beta.class, b2key);
      b3=(Beta)session.load(Beta.class, b3key);
      a1.addBeta(b1);
      a1.addBeta(b2);
      a1.addBeta(b3);
      b1.addAlpha(a1);
      b2.addAlpha(a1);
      b3.addAlpha(a1);
      assertTrue(b1.getAlphas().contains(a1)); //Pass
      assertTrue(b2.getAlphas().contains(a1)); //Pass
      assertTrue(b3.getAlphas().contains(a1)); //Pass
      assertTrue(a1.getBetas().contains(b1)); //Pass
      assertTrue(a1.getBetas().contains(b2)); //Pass
      assertTrue(a1.getBetas().contains(b3)); //Pass
      assertTrue(a2.getBetas().isEmpty()); //Pass
      a1key=a1.getId();
      a2key=a2.getId();
      b1key=b1.getId();
      b2key=b2.getId();
      b3key=b3.getId();
      a1=null;
      a2=null;
      b1=null;
      b2=null;
      b3=null;
      System.gc();
      session.disconnect();
      session=factory.openSession();
      a1=(Alpha)session.load(Alpha.class, a1key);
      a2=(Alpha)session.load(Alpha.class, a2key);      
      b1=(Beta)session.load(Beta.class, b1key);
      b2=(Beta)session.load(Beta.class, b2key);
      b3=(Beta)session.load(Beta.class, b3key);
      assertTrue(!b1.getAlphas().isEmpty());  //Fail.
      assertTrue(!b2.getAlphas().isEmpty());  //Fail.
      assertTrue(!b3.getAlphas().isEmpty());  //Fail.
      assertTrue(!a1.getBetas().isEmpty());   //Fail.
      assertTrue(a2.getBetas().isEmpty());    //Fail.
      assertTrue(b1.getAlphas().contains(a1)); //Fail.
      assertTrue(b2.getAlphas().contains(a1)); //Fail.
      assertTrue(b3.getAlphas().contains(a1)); //Fail.
      assertTrue(a1.getBetas().contains(b1)); //Fail.
      assertTrue(a1.getBetas().contains(b2)); //Fail.
      assertTrue(a1.getBetas().contains(b3)); //Fail.

Name and version of the database you are using: HSQL (Unknown Version. Assuming latest.)

anthony · **Posted:** Thu Sep 02, 2004 3:36 pm

stacktrace?

bdimmick · **Posted:** Thu Sep 02, 2004 3:56 pm

No stacktrace. It just doesn't work.

anthony · **Posted:** Thu Sep 02, 2004 4:08 pm

i just don't see any begin or commit in your code

bdimmick · **Posted:** Fri Sep 03, 2004 8:51 am

If you're referring to creating and commiting a Transaction, I believe you don't have to do as such to save data and have it map correctly. Unless there something needlessly sneaky doing on in the internals....?

bdimmick · **Posted:** Fri Sep 03, 2004 8:57 am

Alright, I added a Transaction around each save and it works now. This is rather perplexing to me, since it seems that many-to-many association mappings aren't getting saved unless they're inside a Transaction, even if the objects which are being mapped are already in Hibernate. (I can understand if they weren't being mapped because they weren't previously saved)[/i]

anthony · **Posted:** Fri Sep 03, 2004 9:04 am

i'm not sure i understand what you're saying... so forgive me if my answer seems strange.

It's known that you must manage the transaction, hibernate doesn't do it for you.

In your case, you should only have 1 beginTrans (at the beginning) and one commit(at the end) + rollback if you catch exceptions.

I advice to use session.flush() to debug.

bdimmick · **Posted:** Fri Sep 03, 2004 9:05 am

But you're not required to use Transactions, correct?

anthony · **Posted:** Fri Sep 03, 2004 9:08 am

see my previsou post, you must at least manage one transaction for a unit of business code (generally one http request).
Of course you don't need to use one transaction per save (or update).

bdimmick · **Posted:** Fri Sep 03, 2004 9:22 am

Is this requirement documented somewhere? The code examples from the Hibernate Manual in section 9.4 do not specify that Transactions are required, and even provide examples without them (although none of them may have any mappings).

I'm not saying this is a bug, but it seems like very unfriendly behaviour, to persist a parent object and not its mapped children just because the operation is not done in a transaction. Moreso, considering that Hibernate doesn't treat this as an error or raise a warning.

steve · **Posted:** Fri Sep 03, 2004 10:25 am

Your hitting a database. Seems common sense that transactions would be needed.

If you are using JTA to manage the transactions for you, then no you don't need to explicitly manage transactions. But otherwise yes.