title: nHibernate, No row with the given identifier exists
body: <p>I have a mapping along the lines of this.</p>
  
  <pre><code>&lt;hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Model.Entities" schema="etl" assembly="Model" default-lazy="false"&gt;
    &lt;class name="Model.Entities.DataField, Model" table="mdm_field"&gt;
      &lt;id name="FieldId" column="field_id" type="int"&gt;
        &lt;generator class="native" /&gt;
      &lt;/id&gt;
      &lt;many-to-one name="KeyField" class="Model.Entities.Key, Model" column="field_id" /&gt;
    &lt;/class&gt;
  &lt;/hibernate-mapping&gt;
  </code></pre>
  
  <p>Now in the database the field_id in the mdm_field table sometimes has a value that does not exist in the related key_field table, so it is basically broken referential integrity. Because of this when I load the entity I get an error "No row with the given identifier exists". How do I configure the mapping to work with this situation so it will not die on this situation.</p>