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PONHibernate relationships with a shared composite key
 

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    <p>I have two tables with composite keys and a linking table between them, like so:</p> <ul> <li><p>A</p> <ul> <li>aid (PK)</li> <li>sharedkey (PK)</li> </ul></li> <li><p>B</p> <ul> <li>bid (PK)</li> <li>sharedkey (PK)</li> </ul></li> <li><p>Linking</p> <ul> <li>aid</li> <li>bid</li> <li>sharedkey</li> <li>sortorder</li> </ul></li> </ul> <p>So the awkward thing there is the shared key, which is part of both FKs. Here's the first thing I tried (I'm using Fluent, but I would have this same problem with XML mappings):</p> <pre><code>mapping.HasManyToMany(x =&gt; x.Bees) .Table("Linking") .ParentKeyColumns.Add("aid", "sharedkey") .ChildKeyColumns.Add("bid", "sharedkey") .OrderBy("sortorder"); </code></pre> <p>Which gives me an mapping exception: "Repeated column in mapping for collection", because I've put in <code>sharedkey</code> twice. That makes sense, because I haven't told in NH that I actually want <code>sharedkey</code> to be the same in each direction.</p> <p>The Java version of Hibernate has a <code>formula</code> <a href="http://docs.jboss.org/hibernate/core/3.3/reference/en/html/example-mappings.html#example-mappings-composite-key-manytomany" rel="nofollow">feature</a> that solves this exactly, but NH, AFAIK, does not. So how can I map this?</p> <p>Some caveats:</p> <ol> <li>It's not totally necessary for this to be in Fluent. XML is fine too</li> <li>This is all read-only, so if the solution breaks inserts in some funny way, that's fine</li> <li>I can't change the DB at all</li> </ol>
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    1. COIf you can create a view in the database, then you can create a wrapping view that exposes the sharedkey column as two different columns, then map to that view.
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    2. CO@eulerfx - yup, thought of that already--I should have mentioned it in the question--and it does work. I'd strongly prefer to avoid it though, because there are tons of these linking tables, which means tons of views (but just one piece of fluent code). It is nice to know I have it as a fallback, though.
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