Entity-engine Unique constraint definition?

[Richard Fleming]

Hi all,
Is there a way to define a database unique constraint when defining an entity 
in the entity-engine.xml file?
It is easy to define a primary key, but I don't see a way to set up a unique 
constraint beyond that.
For instance I'd like to define a unique constraint on the productId and 
brandName fields of theproduct entity. I can do it in the database but....
TIARick