title: NHibernate Mapping Reference without foreign-key
body: <p>I've something like this mapping situation in NHibernate:</p>
  
  <pre><code>ClassA
  mapping.Id(x =&gt; x.Id).Column("rowid").GeneratedBy.Identity().Unique();
  
  ClassB
  mapping.Id(x =&gt; x.Id).Column("rowid").GeneratedBy.Identity().Unique();
  mapping.References&lt;ClassA&gt;(x =&gt; x.ClassA).Nullable();
  </code></pre>
  
  <p>When NHibernate generate the database schema it creates a foreign-key between these tables even if I've specified "Nullable" attribute in mapping declaration. Obivously if I try to save my objects I get a foreign-key constraint error and if I remove manually the foreign-key from database, it works like a charm.</p>
  
  <p>How to tell NHibernate not to create the foreign-key script in this situation? </p>