Criteria API Problem

derKaiser · **Joined:** Mon Jun 19, 2006 9:11 am **Posts:** 3

i thought that it would be possible to define which nested collections or nested persistent classes are loaded and how they are loaded at runtime by using the Criteria api?

But this seems not to be possible:

the DAO-layer:

Code:

   public Concert loadConcert(long id, String[] fetchGroups) {
      Criteria c = this.getSession().createCriteria(Concert.class)
         .add(Restrictions.idEq(id));
      if (fetchGroups != null) {
         for (int i = 0; i < fetchGroups.length; ++i) {

      c = c.setFetchMode(fetchGroups[i], FetchMode.SELECT);
         }
      }
      
      return (Concert) c.uniqueResult();
   }

the buisness-layer

Code:

   public Concert getConcert(long id) {

      Concert conc = this.concertDao.load(id, new String[] { "bands", "location" });
     //session is closed, conc is detached
    return conc;
   }

the mapping file

Code:

<hibernate-mapping>
   <class name="bandzine.domain.Concert" table="CONCERT">
      <id name="id" column="ID">
         <generator class="native"/>
      </id>
      <property name="name" column="NAME"/>
      
      <property name="fromDate" column="FROM_DATE"/>
      <property name="toDate" column="TO_DATE"/>      
      <many-to-one name="location" column="LOCATION_ID" class="bandzine.domain.Location"/>
   

      <set name="bands" table="CONCERT_BAND" lazy="false">
         <key column="CONCERT_ID"/>
         <many-to-many class="bandzine.domain.Band" column="BAND_ID"/>
      </set>
   </class>
   
   <class name="bandzine.domain.Location" table="LOCATION">
      <id name="id" column="ID">
         <generator class="native"/>
      </id>

      <property name="name" column="NAME"/>

      
      <set name="concerts" inverse="true" lazy="false">
         <key column="LOCATION_ID"/>
         <one-to-many class="bandzine.domain.Concert"/>
      </set>      
   </class>   
   
   <class name="bandzine.domain.Band" table="BAND">
      <id name="id" column="ID">
         <generator class="native"/>
      </id>
      <property name="name" column="NAME"/>

      
      <set name="concerts" inverse="true" table="CONCERT_BAND" lazy="false">
         <key column="BAND_ID"/>
         <many-to-many class="bandzine.domain.Concert" column="CONCERT_ID"/>
      </set>   
   </class>

c.setFetchMode(fetchGroups[i], FetchMode.SELECT); does not fetch the nested Objects. So how can i define which nested objects are initialized before detaching at runtime. it only seems to be possible to define it in the xml-mapping by setting the lazy property to lazy="false". But i don't want all nested objects to be loaded every time. i want to be able to create an individual fetch-plan at runtime! ORM like jdo support this, so why not hibernate??

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

FetchMode.SELECT is essentially lazy: if you want to eagerly load, use FetchMode.JOIN. The javadocs for FetchMode are very strange: FetchMode.SELECT says that it's eager, but the docs for FetchMode.LAZY say:

Code:

public static final FetchMode LAZY

    Deprecated. use FetchMode.SELECT

    Fetch lazily. Equivalent to outer-join="false".

I'm not terribly au fait with laziness, but that certainly tells me that SELECT is not what you want.

derKaiser · **Joined:** Mon Jun 19, 2006 9:11 am **Posts:** 3

Thank that's exactly what i wanted to know. But the documentations also tell that using FetchMode.JOIN is imperformant when more than one nested Collection is loaded because of the cartesian product.

So the only way to force Hibernate to fetch nested Collections at Runtime via SELECTs is to execute something like

Code:

Hibernate.initialize(object.getCollection())

, am i right?

thx

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

That's certainly a good way to do it: that guarantees that any associated entities that are referenced more than once have to be loaded only once. FetchMode.JOIN will load every object, every time it's needed.

The alternative is to switch to OpenSessionInView, so that you can lazily load objects whenever you need to, and not worry about eagerly loading things. See http://www.hibernate.org/43.html