title: Order by selection in List view of OpenERP 7.0
body: <p>In OpenERP 7 list view I want to shows the state value sort in the order draft, assigned and cancel currently shows in Asc or Desc. But in my case we need sorting in the order draft, assigned and cancel state. Based on applied in order by in python file</p>
  
  <p>For example in the SQL the code - </p>
  
  <pre><code>select state, date from  object_name
  ORDER BY CASE WHEN state = 'draft'  THEN 0 
                WHEN state = 'assigned'  THEN 1 
                WHEN state = 'cancel'  THEN 2
                ELSE 3
  END,  date desc
  </code></pre>
  
  <p>The above sql code applied in the python</p>
  
  <pre><code>_order = ("CASE WHEN state='draft'  THEN 0",
            "WHEN state = 'assigned'  THEN 1",
            "ELSE 2 END, date desc")
  </code></pre>
  
  <p>In the above query sorting selection value working in the pg_admin but in the python code its shows below error</p>
  
  <pre><code>Invalid "order" specified. A valid "order" specification is a comma-separated
  list of valid field names (optionally followed by asc/desc for the direction)
  </code></pre>
  
  <p>Based on this sorting order by selection value how to apply in OpenERP? Override search method also applied the same sql query but shows same issue.</p>