title: Updating multiple tables with LinqToSql in one unit of work
body: <p>Table 1: int ID-a(pk)</p>
  
  <p>Table 2: int ID-a(pk), int ID-b(pk)</p>
  
  <p>Table 3: int ID-b(pk), string C</p>
  
  <p>I have the data to insert into Table 1. But I do not have the ID-a, which is autogenerated. 
  I have many string C to insert in Table 3.</p>
  
  <p>I am trying to insert row into Table 1, get the ID-a to insert in Table 2 along with the ID-b that is auto-Generated in Table 3 when I submit each string C, all in one submission to db.</p>
  
  <p>Right now I am calling dc.SubmitChanges twice in same call. Is it efficient to have to submit changes twice on same DataContext or  can this be combined further?</p>