title: mapping between 2 collections in mongo DB
body: <p>I would like to do a mapping between 2 collections and modify the value of a property of collection 1 from the value of a property of collection 2</p>
  <p>here the collection 1 :</p>
  <pre><code>{
    &quot;field1&quot;: &quot;value1&quot;,
    &quot;mycode&quot;: &quot;1234&quot;,
    &quot;field3&quot;: &quot;value3&quot;
  }
  </code></pre>
  <p>here is my collection 2 :</p>
  <pre><code>{
     &quot;code&quot;: &quot;1234&quot;,
     &quot;label&quot;: &quot;myLabel&quot;
  }
  </code></pre>
  <p>I want to map the 2 collections with mycode of collection1 and code of collection2 to modify the value of mycode</p>
  <p>here is the expected result :</p>
  <pre><code>{
    &quot;field1&quot;: &quot;value1&quot;,
    &quot;mycode&quot;: &quot;myLabel&quot;,
    &quot;field3&quot;: &quot;value3&quot;
  }
  </code></pre>