title: mongodb aggregation framework match by nested documents
body: <p>I have the following list of documents:</p>
  
  <pre><code>{
      "_id" : "Tvq579754r",
      "name": "Tom",
      "forms": {
             "PreOp":{
               "status":"closed"          
             },
  
             "Alert":{
               "status":"closed"          
             },
  
             "City":{
                "status":"closed"         
             },
  
            "Country":{
               "status":"closed"          
            } 
      }
  },
  ....
  {
      "_id" : "Tvq444454j",
      "name": "Jim",
      "forms": {
            "Jorney":{
               "status":"closed"          
             },
  
            "Women":{
               "status":"void"            
            },
  
           "Child":{
              "status":"closed"           
           },
  
           "Farm":{
             "status":"closed"            
           }  
       }
  }
  </code></pre>
  
  <p>I want to filter them by their 'status' field('forms.name_of_form.status'). I need fetch all documents which don't have 'forms.name_of_form.status' equal 'void'.</p>
  
  <p>Expected result is (document without voided form status):</p>
  
  <pre><code>{
      "_id" : "Tvq579754r",
      "name": "Tom",
      "forms": {
             "PreOp":{
               "status":"closed"          
             },
  
             "Alert":{
               "status":"closed"          
             },
  
             "City":{
                "status":"closed"         
             },
  
            "Country":{
               "status":"closed"          
            } 
      }
  }
  </code></pre>