title: Importing mongo collection into existing collection without overriding it
body: <p>Is it possible to import a mongodump into a existing collection adding to it (not overriding it)? If yes, how?</p>
  
  <p>Would it be using <code>mongoimport --db mydb</code>?</p>
  
  <p>The collections are the same in structure but simple have different datasets from different instances of the same app. I'd like to merge all data into a single database.</p>