title: How can I work with "join" to export data from MongoDB?
body: <p>I have 2 collections:</p>
  
  <p>list1 and list2.</p>
  
  <p>list1 have some fields and list2 have another fields, including the id referring to list1.</p>
  
  <p>I need to do a query to export all items on list1 that have at least one item referring to him on list2.</p>
  
  <p>How can I do this? It's something like a join from list1 to list2. </p>
  
  <p>I need to run a mongoexport command to generate a csv file.</p>