title: Update observable collection by requerying or adding to collection?
body: <p>I have a observable collection exposed as a property within a view model. The observable collection is loaded with objects from a data access layer (linq2sql).</p>
  
  <p>When a new item is added to the database through another view model what is the best way to update the observable collection? Should I repopulate the observable collection with a query to the database or directly insert the new object into the collection?</p>
  
  <p>Also I am still trying to work out how to get one view model to communicate with another one, but I've only been using mvvm for 3 days.</p>