many-to-many with composite id

nickonet · **Posted:** Mon Mar 22, 2004 4:09 pm

Hi-
I need some help on a many-to-many mapping. I have:
Table A:
A1, B1, C1 (composite primary key)
Table B:
B2, C2, D2 (composite primary key)

B1 = B2, C1 = C2. There is a many-to-many relationship between Class1 (table A) and Class2 (Table B).

I have tried the following:

Code:

<class name="Class1" table="TableA">
    <composite-id name="key"  class="Class1PK">
        <key-property name="keyA1" type="long" column="A1"/>
        <key-property name="KeyB1" type="long" column="B1"/>
        <key-property name="KeyC1" type="long" column="C1"/>
   </composite-id>
   ....
   <set name="members" table="TableB" lazy="true">
    <key>
        <column name="B1"/>
        <column name="C1"/>
    </key>
    <many-to-many class="Class2" outer-join="false">
        <column name="D2"/>
     </many-to-many>
  </set>
</class>

and:
<class name="Class2" table="TableB" mutable="false">
   <composite-id name="key" class="Class2PK">
      <key-property name="keyB2" type="long" column="B2"/>
      <key-property name="keyC2" type="long" column="C2"/>
      <key-property name="keyD2" type="long" column="D2"/>
    </composite-id>
    ....
</class>

And I end up with this exception:
net.sf.hibernate.MappingException: Foreign key (TableB [D2])) must have same number of columns as the referenced primary key (TableB [A1,B1,D2]])

If you know the solution you can probably see that I can't figure out which column goes where. I tried other combinations without success. I would appreciate any help on the subject.
Thanks

nickonet · **Posted:** Mon Mar 22, 2004 4:47 pm

Note: I also tried this combination which seemed more correct:
(B1 and C1 are the FK reference to Table B from Table A and
B2, C2 are the FK reference to Table A from Table B):

Code:

<class name="Class1" table="TableA"> 
    <composite-id name="key"  class="Class1PK"> 
        <key-property name="keyA1" type="long" column="A1"/> 
        <key-property name="KeyB1" type="long" column="B1"/> 
        <key-property name="KeyC1" type="long" column="C1"/> 
   </composite-id> 
   .... 
   <set name="members" table="TableB" lazy="true"> 
    <key> 
        <column name="B1"/> 
        <column name="C1"/> 
    </key> 
    <many-to-many class="Class2" outer-join="false"> 
        <column name="B2"/> 
        <column name="C2"/> 
     </many-to-many> 
  </set> 
</class> 

With this error:
net.sf.hibernate.MappingException: Foreign key (TableB [B2,C2])) must have same number of columns as the referenced primary key (TableA [A1,B1,C1])

nickonet · **Posted:** Mon Mar 22, 2004 8:30 pm

I have overlooked the fact that a third table is required by Hibernate. I am not sure I understand why it is the case. The above pattern doesn't seem incorrect to me and being able to link two classes/tables like that should be common.