loading a collection without loading the parent

matteo.smith@gmail.com · **Joined:** Fri Mar 04, 2005 2:13 am **Posts:** 3

I have the following pieces of information in a parent-child association:

and I would like to load the child collection without loading the parent instance. Is this possible?

For example:

Code:

class Parent {
  Long id;
  Set childCollection;
  Set otherCollection;
}

class Child {
  Long id;
  Parent parent;
  //etc..
}

class Other {
  Long id;
  Parent parent;
  //etc..
}

public Collection load(Class parent, Long id, String association) {
   ... how to implement?
}

With possible hibernate mappings:

Code:

   <class name="Parent" table="T_PARENT" lazy="true" mutable="true" polymorphism="implicit" dynamic-update="false" dynamic-insert="false" batch-size="1" select-before-update="false" optimistic-lock="version">
      <id name="Id" column="Id" type="java.lang.Long">
         <generator class="native"/>
      </id>
      <!-- bi-directional one-to-many association to Child -->
      <set name="childCollection" table="T_Child" lazy="true" cascade="all" sort="unsorted" inverse="true" batch-size="1" outer-join="auto">
         <key column="parentId"/>
         <one-to-many class="Child"/>
      </set>
      <!-- bi-directional one-to-many association to Other -->
      <set name="otherCollection" table="T_Other" lazy="true" cascade="all" sort="unsorted" inverse="true" batch-size="1" outer-join="auto">
         <key column="parentId"/>
         <one-to-many class="Other"/>
      </set>
   </class>
   <class name="Child" table="T_CHILD" lazy="true" mutable="true" polymorphism="implicit" dynamic-update="false" dynamic-insert="false" batch-size="1" select-before-update="false" optimistic-lock="version">
      <id name="Id" column="Id" type="java.lang.Long">
         <generator class="native"/>
      </id>
      <!-- bi-directional many-to-one association to Parent -->
      <many-to-one name="parent" class="Parent" not-null="true" cascade="none" unique="false" outer-join="auto" update="true" insert="true">
         <column name="parentIId"/>
      </many-to-one>
   </class>
   <class name="Other" table="T_OTHER" lazy="true" mutable="true" polymorphism="implicit" dynamic-update="false" dynamic-insert="false" batch-size="1" select-before-update="false" optimistic-lock="version">
      <id name="Id" column="Id" type="java.lang.Long">
         <generator class="native"/>
      </id>
      <!-- bi-directional many-to-one association to Parent -->
      <many-to-one name="parent" class="Parent" not-null="true" cascade="none" unique="false" outer-join="auto" update="true" insert="true">
         <column name="parentId"/>
      </many-to-one>
   </class>

I have a generic loader that gets Parent.class, "childCollection", and 1445 as the id of parent. But I don't know, for example, the property name of the child that references the parent (so I can't just go "select Child where child.parentid = 1445"). Is there a way I can load the children in one shot, without going through the extra step of loading the parent?

Thanks,
-Matt

Hibernate version: 2.1.6

Name and version of the database you are using: Oracle 9i

borak · **Posted:** Thu Mar 10, 2005 6:09 am

Use that query:
select c from Child as c where c.parent.id = 1445

matteo.smith@gmail.com · **Joined:** Fri Mar 04, 2005 2:13 am **Posts:** 3

Perhaps I should have used a slighly different example. The actual situation is more like this:

Code:

class Parent {
  Long id;
  Set childCollection;
  Set otherCollection;
}

class Child {
  Long id;
  Parent parentOfChild;
  //etc..
}

class Other {
  Long id;
  Parent parentOfOther;
  //etc..
}

public Collection load(Class parent, Long id, String association) {
   ... how to implement?
}

So "parent" isn't always the name of the association. So all I have a handle to is the "many" end of the bi-di association. - I'd get a call like load(Parent.class, 1445, "childCollection"). Any way to load that?

Thanks,
-Matt

borak · **Posted:** Tue Mar 15, 2005 5:37 am

Simpliest way:
Use an upper-class where Child and Other extends that class , since Child and Other has ID and parent variables, move them up to that class, then
"parent" will always be the name of the association.