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POStoring an ordered child collection in NHibernate
 

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    <p>I'm having trouble getting my head around the way I should implement an ordered child relationship with NH.</p> <p>In the code world, I have:</p> <pre><code>class Parent { public Guid Id; public IList&lt;Child&gt; Children; } class Child { public Guid Id; public Parent Parent; } </code></pre> <p>A <code>Parent</code> has a list of <code>Child[ren]</code> with an order. In reality, the <code>Children</code> collection will contain unique <code>Child</code>s which will be enforced by other code (i.e. it will never be possible to add the same child to the collection twice - so i dont <em>really care</em> if the NH collection enforces this)</p> <p>How should I implement the mappings for both classes?</p> <p>From my understanding:</p> <ul> <li><code>Bags</code> have no order, so i dont want this</li> <li><code>Sets</code> have no order, but i could use <code>order-by</code> to do some sql ordering, but what do i order by? I can't rely on a sequential ID. so i dont want this?</li> <li><code>Lists</code> are a duplicate-free collection, where the unique-key is the <code>PK</code> and the <code>index</code> column, so i do want this?</li> </ul> <p>So, using a <code>list</code>, i have the following:</p> <pre><code>&lt;list cascade="all-delete-orphan" inverse="true" name="Children"&gt; &lt;key&gt; &lt;column name="Parent_id" /&gt; &lt;/key&gt; &lt;index&gt; &lt;column name="SortOrder" /&gt; &lt;/index&gt; &lt;one-to-many class="Child" /&gt; &lt;/list&gt; </code></pre> <p>When I insert a parent which a child on it, i see the following SQL:</p> <pre><code>Insert into Child (id, Parent_id) values (@p0, @p1) </code></pre> <p>I.e, why doesn't it insert the SortOrder?</p> <p>If I do a <code>SchemaExport</code> the SortOrder column is created on the Child table.</p> <p>:(</p> <p>If I set <code>Inverse="false"</code> on the relationship, i see the same SQL as above, followed by:</p> <pre><code>UPDATE "Child" SET Parent_id = @p0, SortOrder = @p1 WHERE Id = @p2 </code></pre> <p>Why does it still <code>INSERT</code> the Parent_id with <code>inverse="false"</code> and why doesn't it insert the SortOrder with <code>inverse="true"</code>?</p> <p>Am I approaching this totally wrong?</p> <p>Is it also true that assuming this was working, if I were to do:</p> <pre><code>parentInstance.Children.Remove(parentInstance.Children[0]); </code></pre> <p>save the parent and reload it, that the <code>list</code> would have a null in position 0, instead of shuffling the rest up?</p> <p>Thanks</p>
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    1. USAndrew Bullock
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