title: mongodb meaning of dot and a dollar sign
body: <p>I am debugging a code which used flask_pymongo</p>
  
  <p>and I see this code </p>
  
  <pre><code>   dabb = mongo.db.tbl.find({
              "transactions": {'$elemMatch': {"from":{'$elemMatch':{"from":str(to)}},"to":{'$elemMatch':{"to":str(frm)}}}}
          },{"transactions.$": 1 })
  </code></pre>
  
  <p>I don't understand what does that {"transactions.$": 1 } do. </p>
  
  <p><a href="https://i.stack.imgur.com/5a1oK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5a1oK.png" alt="enter image description here"></a></p>