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PONHibernate mapping - one-to-one (or one-to-zero)
 

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    <p>NHibernatians!</p> <p>I have a table [dbo].[Wibble] and another table [dbo].[WibbleExtended].</p> <p>[Wibble] is the main table and [WibbleExtended] is an optional table where some other fields are stored. There are far fewer entries in the [WibbleExtended] table than the main [Wibble] table. I think this was done back in the day to cure some space issues (Wibble has many rows and WibbleExtened has many columns).</p> <p>The ID for each table is the same and comes from an external source. </p> <p>I.e.</p> <pre><code>[dbo].[Wibble].[WibbleId] </code></pre> <p>and </p> <pre><code>[dbo].[WibbleExtended].[WibbleId] </code></pre> <p>are identical and is how the two tables relate.</p> <p>N.B. I can't change the schema. I'm shoe-horning this onto a legacy system that I have almost no control over.</p> <p>Searching around it seems that one-to-one mappings are problematic and the prevailing wisdom is to use two many-to-one mappings.</p> <p>My mappings currently are:</p> <pre><code>&lt;class name="Wibble" table="Wibble" &gt; &lt;id name="Id" column="WibbleId" type="Int32"&gt; &lt;generator class="assigned"/&gt; &lt;/id&gt; &lt;many-to-one name="WibbleExtended" class="WibbleExtended" column="WibbleId" not-null="false" cascade="all"/&gt; &lt;/class&gt; </code></pre> <p>And</p> <pre><code>&lt;class name="WibbleExtended" table="WibbleExtended" &gt; &lt;id name="Id" column="WibbleId" type="Int32"&gt; &lt;generator class="assigned" /&gt; &lt;/id&gt; &lt;many-to-one name="Wibble" class="Wibble" column="WibbleId" not-null="true" /&gt; &lt;/class&gt; </code></pre> <p>The problem with this is I'm getting errors such as </p> <pre><code>System.IndexOutOfRangeException: Invalid index n for this SqlParameterCollection with Count=n. </code></pre> <p>I've looked around and this does look like the correct strategy, it's just falling at the final hurdle.</p> <p>Is the problem the id generator? Other aspect of the mapping?</p> <p>Free mince pie for the correct answer.</p> <p>EDIT: Ok - here's what I did to solve this via @James Gregory.</p> <ol> <li><p>Moved the unit tests from the WibbleExtended tests to the Wibble test class and made the necessary modifications.</p></li> <li><p>Added the following to the Wibble.hbm.xml </p> <pre><code>&lt;join table="WibbleExtended" optional="true"&gt; &lt;key column="WibbleId"/&gt; &lt;property name="Blah1" column="Blah1" type="String" length="2000" not-null="false" /&gt; &lt;property name="Blah2" column="Blah2" type="String" length="1000" not-null="false" /&gt; &lt;/join&gt; </code></pre></li> <li><p>Added the corresponding properties to the Wibble POCO.</p></li> <li><p>Deleted all code relating to WibbleExtended.</p></li> <li><p>Run tests, all passed, checked in. Build passed. Went for an xmas beer (hence it's been a couple of days before I updated this! :-))</p></li> </ol>
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