title: How to append to existing documents using mongoimport and csv files
body: <p>I am trying to use mongoimport to translate a one-to-many relational structure into mongoDB using csv files.  My approach is to import the "one" file then use the upsert option to append the "many" records as a nested array but it looks like it only replaces the original document instead of appending.</p>
  
  <p>Is this a limitation of mongoimport or could I be doing something wrong?  </p>