single class to multiple table mapping

snowwolf · **Joined:** Mon Nov 26, 2007 12:11 pm **Posts:** 1

I see single class to multiple table mapping is a feature on the roadmap for nHibernate, so I am trying to do this the simplest way possible until then.

What are the recommended solutions?

I was hoping I could do something like:

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
               namespace="Survey.Domain"
               assembly="Survey.Domain"
               default-access="field.camelcase-underscore">
   <class name="Survey">
      <id name="SurveyId">
         <generator class="native" />
      </id>
      <property name="SurveyName" />
      <property name="ExternalId" />
      <property name="IsLive" />
      <property name="Score" />
      <property name="ReviewCount" />

      <loader query-ref="GetSurvey"/>
   </class>

   <sql-query name="GetSurvey">
      <return alias="survey" class="Survey"/>
      <![CDATA[SELECT tbl_survey.SurveyId,
      tbl_survey.SurveyName, 
      tbl_survey.ExternalId,
      tbl_survey.IsLive,
      tbl_survey_rating.Score,
      tbl_survey_rating.ReviewCount
      FROM tbl_survey
      LEFT OUTER JOIN tbl_survey_rating ON tbl_survey.ExternalId = tbl_survey_rating.ExternalId]]>
   </sql-query>

</hibernate-mapping>

karlchu · **Posted:** Mon Nov 26, 2007 1:22 pm

You can use a <one-to-one>; and that's probably the simplest.

If you proceed with the way you outlined (using <loader>), you would also have to use <sql-insert>, <sql-update>, and <sql-delete> to tell NH how to do those operations.

An alternative would be to map to a database view, provided the DBMS you are using allows writable views. With MS SQL, you can create triggers on the view to simulate writable views.

If you don't mind living on the edge a bit, you can check out the source from the trunk. It has the <join> element; although it has a fairly major issue (NH-1059) when applied to a <subclass>.