title: Add or Update an entity without knowing if its exists
body: <p>I have a group of entities that I don't know if they already exists in the Database.
  If they exists - I need to update them, if they does not exists - I need to add them (for each entity it might be one or the other, and there are 10000 of them...)</p>
  
  <p>(scenario - I'm importing data from a file, if I import the same file - nothing should happen, if the file is changed - I need to update).</p>
  
  <p>Can I achieve it with Entity Framework without having to search for each entity before I add it ?</p>
  
  <p>(if I want to add - I need to use AddObject, if I want to modify - I need to use attach and ChangeObjectState).</p>
  
  <p>is there a way to avoid the search - than do one of the 2 options ? </p>
  
  <p>(looking for "Add or Update" way....)</p>
  
  <p>Thanks.</p>