title: Add an attribute to an existing document in MongoDB
body: <p>I have a mongoDB collection like this:</p>
  
  <pre><code>{
      "_id" : ObjectId("54bd056621396c50b6da3d4
      "name" : "Nagaland",
      "districts" : [
              {
                      "name" : "Wokha",
                      "population" : {
                              "2011" : 161223
                      }
              },
              {
                      "name" : "Mokokchung",
                      "population" : {
                              "2011" : 232085
                      }
              },
              {
                      "name" : "Zunheboto",
                      "population" : {
                              "2011" : 153955
                      }
              }
      ]}
  </code></pre>
  
  <p>Now later I want to add some more attributes to each of the districts like location,sex-ratio etc. How do I do it? When I use update it is adding to the parent not inside a particular district.</p>