Many-to-Many converted to a many-to-one

duggant · **Joined:** Mon May 03, 2004 1:25 pm **Posts:** 31

I have a many-to-many relationship in the db but the domain models it as a many-to-one. Is there anyway to map the relationship as a many-to-one, so that I end up with multiple instances of countysurvey (one for each marketsegment)?

I'm using Hibernate 2.1 against an oracle 9i db.

Thanks,
Tim

Code:

<class name="MarketSegment" table="GDR_PROD.MKT_SEG">
        <jcs-cache usage="read-only"/>
        <id name="id" type="long" column="MKT_SEG_GNMBR">
            <generator class="assigned"/>
        </id>
            
        <set name="countySurveys" table="GDR_PROD.MKT_SEG_SMPL_GEO" lazy="false">
         <key column="MS_MKT_SEG_GNMBR"/>
         <many-to-many column="SG_SMPL_GEO_GNMBR" class="CountySurvey"/>
      </set>
      
   </class>
   
   <class name="CountySurvey" table="GDR_PROD.SMPL_GEO">
        <jcs-cache usage="read-only"/>
        <id name="id" type="int" column="SMPL_GEO_GNMBR">
            <generator class="assigned"/>
        </id>
        <property name="name" column="SMPL_GEO_NAME"/>
      
        <set name="marketSegments" table="GDR_PROD.MKT_SEG_SMPL_GEO" lazy="false">
         <key column="SG_SMPL_GEO_GNMBR"/>
         <many-to-many column="MS_MKT_SEG_GNMBR" class="MarketSegment"/>
      </set>
         
    </class>

anthony · **Posted:** Fri Jun 04, 2004 10:37 am

no you can't map this virtual many to one with hibernate, it must be a many to many.

But what you can do is to declare your marketSegment property (which means many to one in your domain model) and in the :
- setMarketSegments() code marketSegment = (MarketSegment)marketSegments.get(0)
- and in the setMarketSegment code marketSegments.set(0,marketSegment)

marketSegments will be your persistent mapped property
marketSegment will be your business property

duggant · **Joined:** Mon May 03, 2004 1:25 pm **Posts:** 31

I thought of that, but there's more than one segment, so I have to create new countysurvey objects for each one.

anthony · **Posted:** Fri Jun 04, 2004 10:43 am

so why don't you just keep many to many semantics?

duggant · **Joined:** Mon May 03, 2004 1:25 pm **Posts:** 31

I'm sorry your first post was the solution. Essentially, when the domain asks for the CountySurveys from MarketSegment, I'll populate the setMarketSegment() business method, with the current marketsegment.

Thanks,
Tim