title: RailsAdmin not figuring out composite key
body: <p>I have a table in postgres with a composite key. I am trying to access it using rails_admin.</p>
  
  <p>Model.rb:</p>
  
  <pre><code> class ModelName &lt; ActiveRecord::Base
    self.table_name = 'schema.tablename'
    establish_connection :db
  end
  </code></pre>
  
  <p>I can see the count of rows and the table name and everything. But when I click on the table in the admin UI, it fails with this error</p>
  
  <p><code>: SELECT  "schema"."tablename".* FROM "schema"."tablename" ORDER BY schema.tablename. desc LIMIT 20 OFFSET 0</code></p>
  
  <p>The id is missing in the order by clause. Is this because it is a composite id? How do I get rails admin to properly identify the id of the table?</p>