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POYet another many-to-many NHibernate question
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  1. POYet another many-to-many NHibernate question
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    copied!<p>Trying to implement relatively simple relationship between <code>User</code> and <code>Role</code>. <code>User</code> can be in many roles, same <code>Role</code> can belong to any number of <code>User</code>s. <code>Role</code>s are shared, i.e. all <em>admin</em> <code>User</code>s refer to the very same instance of class <code>Role</code>.</p> <p><code>User</code> mapping:</p> <pre><code> &lt;class name="User" lazy="false" table="Users"&gt; &lt;id name="Id" type="int"&gt; &lt;generator class="native"/&gt; &lt;/id&gt; &lt;property name="Name" column="Username" /&gt; &lt;bag name="RoleList" table="User_Role" inverse="true" lazy="false" cascade="save-update"&gt; &lt;key column="UserId" foreign-key="Id"/&gt; &lt;many-to-many class="Role" column="RoleId"/&gt; &lt;/bag&gt; &lt;/class&gt; </code></pre> <p><code>Role</code> mapping:</p> <pre><code> &lt;class name="Role" lazy="false" table="Roles"&gt; &lt;id name="Id" type="int"&gt; &lt;generator class="native"/&gt; &lt;/id&gt; &lt;property name="Name" column="Rolename"/&gt; &lt;property name="Description"/&gt; &lt;/class&gt; </code></pre> <p>There are three DB tables: one for <code>User</code>s, one for <code>Role</code>s and the third is for the many-to-many relation (with two foreign keys: <code>UserId</code> and <code>RoleId</code>). A primary key is the composite key of those two.</p> <p>The problematic <em>scenario</em>: the roles are predefined. In my C# code I am constructing a <em>user</em>, while attaching the <em>role</em> to it. The role is an object that was successfully fetched from DB with correct <em>id</em>. I am trying to save that <em>user</em> in the database.</p> <p>Now to the <strong>question</strong>: I am receiving a <em>duplicate key</em> DB error, since NHibernate is trying to insert the <code>Role</code> object into the appropriate table. Since the <code>RoleId</code> already belongs to the existing <em>role</em>, I would expect that no new role will be inserted in DB.</p> <p><em>Gory details</em>: I've also tried to debug the NHibernate and seen that for some reason <code>EntityIdentityInsertAction</code> receives a <code>Role</code> and calls base constructor. In the call to the base constructor the <code>Id</code> parameter is a simple hard-coded <em>null</em>. The stack trace also contains a call to <code>SaveWithGeneratedId()</code> (somewhere earlier in the chain), which implies that the <code>Id</code> for the existing <code>Role</code> object is not counted for some reason.</p> <p>This is all the info I've succeeded to find so far. Please tell what am I doing wrong.</p>
 

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