title: Referential constraint based on substring of value in EF4?
body: <p>In EF4 is it possible to have a referential contstraint which is based upon just a substring of a value?</p>
  
  <p>e.g.</p>
  
  <p>Ref table:
  Code: varchar(5)
  Desc: varchar(50)</p>
  
  <p>Main Table:
  Code: varchar(6)
  Data1:
  Data2: etc...</p>
  
  <p>I would like to have a constraint where <code>MainTable.Code.Substring(0,5) &gt; RefTable.Code</code></p>
  
  <p>Is that possible?</p>