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mapping a Map whose key is a domain object and values sets

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ferdydurke

Post subject: mapping a Map whose key is a domain object and values sets

Posted: Sun Aug 21, 2005 2:31 pm

Newbie

Joined: Wed Aug 17, 2005 12:35 pm
Posts: 5

Is there a way to map (ehm :-)) a Map whose keys are one of my domain objects and the values are Set(s) of other domain objects?

I just can find examples of mapping hibernate types to hibernate types or elements (or composite elements) but I would like to map to association.

Thanks

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michaelcourcy

Post subject:

Posted: Sun Aug 21, 2005 5:00 pm

Beginner

Joined: Sun Jul 31, 2005 6:15 pm
Posts: 28

It's the role of the join table, isnt't it ?

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ferdydurke

Post subject:

Posted: Sun Aug 21, 2005 7:51 pm

Newbie

Joined: Wed Aug 17, 2005 12:35 pm
Posts: 5

I don't understand exactly what you mean but this is not a simple one-to-many or many-to-one association.

It's a map association, suppose you have a map where the key is an object and the value is a list of objects:

Code:

class ClassA {

    private HashMap associatedClassB;

    ClassA() {

        HashMap associatedClassB = new HashMap();
        ClassC classC = new ClassC();

        this.getAssociatedClassB(classC).add(new ClassB());
        this.getAssociatedClassB(classC).add(new ClassB());
        ....
        
    }
    .....

    public Map getAssociatedClassB() {

         return this.associatedClassB;

   }

}

To my understanding the mapping xml could be

Code:

   <class
            name="ClassA"
            table="table_class_a"
        >
         

        <map
            name="associatedClassB"
            lazy="false"
            sort="unsorted"
            cascade="save-update"
        >

            <key  column="associated_class_b_id"/>
            

            <one-to-many
                  class="ClassB"
            />
            
            <map-key-many-to-many column="associated_class_b_key"
             class="ClassC"/>
    
         </map>
    

 </class>

but this is not the case, I receive the following error:

Code:

The content of element type "map" must match "(meta*,subselect?,cache?,synchronize*,comment?,key,(map-key|composite-map-key|map-key-many-to-many|index|composite-index|index-many-to-many|index-many-to-any),(element|one-to-many|many-to-many|composite-element|many-to-any),loader?,sql-insert?,sql-update?,sql-delete?,sql-delete-all?,filter*)".

that looks quite strange to me as it looks like all mandatory subelements are at their place...

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ferdydurke

Post subject:

Posted: Tue Aug 23, 2005 8:09 am

Newbie

Joined: Wed Aug 17, 2005 12:35 pm
Posts: 5

Ok, I got to some (partial) conclusion and I report it here hoping ic can be of some help for someone:

my error was that I was looking for a many-to-many association for values, not a one-to-many! so My mapping would be:

Code:

<class name="ClassA">

...

<map name="associatedClassB" table="classc_classb_map">
    <!-- the foreign key column linking the a map table row to the class table row to where the map belongs -->
    <key  column="classa_id"/>

    <!-- The map key referencing the id of a ClassC instance -->
    <map-key-many-to-many column="classc_id" class="ClassC"/> 

    <!-- The map value referencing the id of a ClassB instance (table row) -->
    <many-to-many class="ClassB" column="classb_id"/>

</map>

...

</class>

now the problem is that this mapping still maps a ClassC key with a SINGLE ClassB value because the generated table has classa_id and classc_id as primary keys while classb_id is allowed to be the same.

To have a ClassC -> "list of ClassB" mapping would be enough to have all three "_id" columns as primary keys... I wonder if Hibernate is able to map this... I would you express this in hte mapping file?

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lkline

Post subject:

Posted: Wed Sep 21, 2005 1:29 pm

Beginner

Joined: Wed Sep 21, 2005 11:52 am
Posts: 43

<map-key-many-to-many .../> is not a valid subelement of <map>. I used <index-many-to-many .../> which worked and generated appropriate ddl.

Larry

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rmorales

Post subject:

Posted: Wed Nov 30, 2005 1:23 pm

Newbie

Joined: Fri Oct 14, 2005 8:37 am
Posts: 10
Location: University of Edinburgh

Actually, map-key-many-to-many is a valid sub-element of map. I have got:

Code:

  <class name="ClassA">
    <id type="long">
      <generator class="native"/>
    </id>

    <map name="associatedClassB" inverse="true" cascade="all,delete-orphan">
      <key column="classAId"/>
      <map-key-many-to-many class="ClassC"
        column="classCId" />
      <one-to-many class="ClassB"/>
    </map>
  </class>

My problem in this case is that both classAId and classBId are set as
separated foreign keys, rather than as a single (composite) foreign key.
Any ideas?

Rafael

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rmorales

Post subject:

Posted: Wed Nov 30, 2005 1:25 pm

Newbie

Joined: Fri Oct 14, 2005 8:37 am
Posts: 10
Location: University of Edinburgh

Actually, map-key-many-to-many is a valid sub-element of map. I have got:

Code:

  <class name="ClassA">
    <id type="long">
      <generator class="native"/>
    </id>

    <map name="associatedClassB" inverse="true" cascade="all,delete-orphan">
      <key column="classAId"/>
      <map-key-many-to-many class="ClassC"
        column="classCId" />
      <one-to-many class="ClassB"/>
    </map>
  </class>

My problem in this case is that both classAId and classBId are set as
separated foreign keys, rather than as a single (composite) foreign key.
Any ideas?

Rafael

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