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Question on Legacy Database Collection Mapping

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scarpen

Post subject: Question on Legacy Database Collection Mapping

Posted: Wed Sep 26, 2007 11:50 am

Newbie

Joined: Wed Sep 26, 2007 11:26 am
Posts: 2

NHibernate version: 1.2.0.4000
Name and version of the database you are using: SQL Server 2000

I have a legacy SQL Server 2000 database that has some interesting link tables used for collections. An example:

Code:

 ______________________
| Documents            |
|______________________|
| DocId(int) *         |
| TagCollectionId(int) |
|______________________|

 _______________________
| TagCollection         |
|_______________________|
| TagCollectionId* (int)|
| Order*(int)           |
| ItemId*(int)          |
|_______________________|

 _________________________
| Tags                    |
|_________________________|
| ItemId*(int)            |
| Description(varchar(25) |
|_________________________|

The problem I'm having is how to map the TagCollection and Tag tables with the Documents table. I'd like to have a Document class with a Tags property, but I'm not sure if that's feasible or if I need a TagCollection class as well (I'm thinking yes because of the Order column, but I'm not sure). Further complicating things (at least for me) is the fact that the TagCollection table does not contain a DocId column, but instead the TagCollectionId from the Documents table.

Any advice on how to proceed with this type of mapping is appreciated.

Thanks,
Sean Carpenter

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scarpen

Post subject:

Posted: Fri Sep 28, 2007 11:17 am

Newbie

Joined: Wed Sep 26, 2007 11:26 am
Posts: 2

I have an update on this issue.

I was able to make this work in Hibernate 3.2.5 using property-ref attributes like this:
Documents.hbm.xml

Code:

<class name="Documents" table="Documents" schema="dbo" catalog="Hibernate">
        <id name="docId" type="string">
            <column name="DocId" />
            <generator class="assigned" />
        </id>
        <property name="tagCollectionId" type="string">
            <column name="TagCollectionID" unique="true" />
        </property>
        <set name="tags" table="TagCollection">
            <key property-ref="tagCollectionId">
                <column name="TagCollectionId" not-null="true" />
            </key>
            <many-to-many column="ItemID" class="Tags" />
        </set>
    </class>

and Tags.hbm.xml

Code:

<class name="Tags" table="Tags" schema="dbo" catalog="Hibernate">
        <id name="itemId" type="string">
            <column name="ItemID" />
            <generator class="assigned" />
        </id>
        </property>
        <property name="description" type="string">
            <column name="Description" />
        </property>
        <set name="documents" inverse="true" table="TagCollection">
            <key>
                <column name="ItemID" not-null="true" />
            </key>
            <many-to-many class="Documents" property-ref="tagCollectionId" column="TagCollectionID" />
        </set>
    </class>

The problem now is that the property-ref attribute does not exist for <key> or <many-to-many> elements in NHibernate. I'm going to look at other ways of mapping as well as what it would take to add this functionality to NHibernate (a JIRA issue already exists).

Sean Carpenter

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