title: Omit certain field in an array mongo query
body: <p>Similar to <a href="https://stackoverflow.com/questions/17075205/query-for-a-field-in-an-object-in-array-with-mongo">Query for a field in an object in array with Mongo?</a> The asker want to query a specific field in an object, but what I want is opposite to him.</p>
  
  <p>My data</p>
  
  <pre><code>{   "_id": "ffb76dea811a6773c9481fd35262fe7f", 
      "fieldA" : "A", 
      "fieldB" : "B", 
      "fieldC" : [ 
          { "group1" : "100", "group2" : "200", "id" : "b0a05edd3cb0d35674174f34da1b3021"}, 
          { "group1" : "110", "group2" : "230", "id" : "b9071b34c21f948e69cb39df7dbf10a7"} 
      ]
  }
  </code></pre>
  
  <p>How to query to get</p>
  
  <pre><code>{
      "fieldA" : "A", 
      "fieldC" : [ 
          { "group1" : "100", "group2" : "200" }, 
          { "group1" : "110", "group2" : "230" } 
      ]
  }
  </code></pre>
  
  <p><strong>Key point is that I don't want <code>id</code> appear in my query result</strong></p>
  
  <pre><code>db.test.insertOne({"_id":"ffb76dea811a6773c9481fd35262fe7f","fieldA":"A","fieldB":"B","fieldC":[{"group1":"100","group2":"200","id":"b0a05edd3cb0d35674174f34da1b3021"},{"group1":"110","group2":"230","id":"b9071b34c21f948e69cb39df7dbf10a7"}]})
  </code></pre>