title: Update query in LINQ contains all columns in WHERE clause instead of just the primary key column
body: <p>I am updating a single column in a table using Linq, take fictitious table below.</p>
  <p>MyTable (PKID, ColumnToUpdate, SomeRandomColumn)</p>
  <pre><code>var row = (from x in DataContext.MyTable
             where b.PKID == 5
             select x).FirstOrDefault();
  
  row.ColumnToUpdate = 20;
  DataContext.SubmitChanges();
  </code></pre>
  <p>This updates the column to as expected, no surprises here. However when I inspect the SQL commands which are generated, it does this:</p>
  <pre><code>UPDATE [dbo].[MyTable ]
  SET [ColumnToUpdate ] = @p2
  WHERE ([PKID] = @p0) AND ([SomeRandomColumn] = @p1) 
  </code></pre>
  <p>This is performing the update, but only if all columns have matched the values of what Entity expects them to be, rather than referencing the Primary Key column on it's own.</p>
  <p>If a database column is changed by another process, which is very feasible in this particular project; eg. There is a window between getting the row you want to manipulate, calculating the changes you would like to set the value to, and issuing the update command as a batch of rows. In this situation the query will cause an exception, causing a partial update, unless I trap, reload the data and resend individual queries. It also has a downside that the row information can be quite large (ie, containing HTML mark up for instance), and the whole thing gets passed to SQL and slows the system down when larger batches are processed.</p>
  <p>Is there a way of making Linq / Entity to issue update commands based only on the PK column in the Where clause?</p>