Provide a declarative, performant mechanism to prevent duplicate document names within a folder

Enhance the content repository with the ability to declaratively prevent duplicate document names within a folder. Alfresco supports this capability using the boolean "duplicate" element within a child association as follows: (http://wiki.alfresco.com/wiki/Data_Dictionary_Guide#Child_Associations)

<type name="cm:folder">
<title>Folder</title>
<parent>cm:cmobject</parent>
<associations>
<child-association name="cm:contains">
<source>
<mandatory>false</mandatory>
<many>false</many>
</source>
<target>
<class>sys:base</class>
<mandatory>false</mandatory>
<many>true</many>
</target>
<duplicate>false</duplicate>
<propagateTimestamps>true</propagateTimestamps>
</child-association>
</associations>
</type>

Alfresco uses database constraint to performantly implement this feature. Nuxeo should consider providing a similar capability.