Is the documentation incorrect? seam reference docs wrote : | @DataModel | | Exposes an attribute of type List, Map, Set or Object[] as a JSF DataModel into the scope of the owning component... | I believe that the standard JSF datatable only supports a limited number of types (not java.util.Set ) which seems to cause problems for one-to-many relationships where the "most natural" type of association is a Set. The hibernate documentation seems to really make a point of this being the most correct mapping where there are not any duplicates but then you can't render it using the stock datatable. The last time I tried it the MyFaces implementation actually "incorrectly" supported the rendering of a Set within a datatable but there were discussions about "fixing" the implementation to not support it. Can you show how you add to the Collection? and mabye the .xhtml (assuming Facelets) View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4037799#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...