title: Duplicate mongoose Documents
body: <p>I'm looking for a very simple way to duplicate a document in my DB but can't find a way to do it.</p>
  
  <p>I have 2 models with the exact same schema.</p>
  
  <p>What i'm doing is </p>
  
  <pre><code>  1stDB.findOne({id:"1"}, function(error, results){
     if(!error){
          var 2ndb = new 2nDB(results);
          2nd.save(function (err) {
          if (err) {
            return err;
          }
          else {
            console.log("SUCCESSFULL");
          }
        });
   }
  })
  </code></pre>
  
  <p>There seems to be an issue as in my console <code>results</code> is formatted properly but just wont save. </p>
  
  <p>But if i do it manually  : <code>2ndb.anyfield = anyvalue</code> it works.</p>
  
  <p>I think it might have to do with promise ? but i'm not very familiar with the concept and might be wrong.</p>
  
  <p>I've tried this :</p>
  
  <pre><code>  1stDB.findOne({id:"1"}, function(error, results){
     if(!error){
          var 2ndb = new 2nDB(**{results}**);
          2nd.save(function (err) {
          if (err) {
            return err;
          }
          else {
            console.log("SUCCESSFULL");
          }
        });
   }
  })
  </code></pre>
  
  <p>and this ( In the hope that deleting the _id and keeping my custom .id field to identify similar document but still having an uniq _id by document would work but it didn't )</p>
  
  <pre><code>  1stDB.findOne({id:"1"}, function(error, results){
     if(!error){
          **var objectResponse = results;
          delete objectResponse._id;**
          var 2ndb = new 2nDB(results);
          2nd.save(function (err) {
          if (err) {
            return err;
          }
          else {
            console.log("SUCCESSFULL");
          }
        });
   }
  })
  </code></pre>