title: Map in Mongoose
body: <p>I'm trying to create a schema in Mongoose that have a map (object, associative array, key-value pairs), but no success so far.<br>
  The documents of my schema must be something like this:</p>
  
  <pre><code>{
      "_id": ObjectId("..."),
      "groups"
      {
          "groupA":
          {
              "value1": "...",
              "value2": "..."
          },
          "groupB":
          {
              "value3": "...",
          },
          "groupC":
          {
              "value4": "...",
              "value5": "...",
          },
          ...
      }
  }
  </code></pre>
  
  <p><strong>groups</strong> is as object with a <em>variable number of keys</em>. I don't know those keys ahead of time as it'll be create by the user.<br>
  Every entry in groups is another object. As before, I don't know the key identifiers, but I know that the values are <em>String</em> (or Boolean, or Number, doesn't matter).<br>
  Of course, those keys are <em>Strings</em>.</p>
  
  <p>Is it even possible (is there anyway to build such schema/model) in Mongoose?</p>