title: Mongoose : don't insert if element already stored
body: <p>I'm using MongoDB and Mongoose with Express to store tweets that I retrieve via the Twitter API.</p>
  
  <p>I want to avoid saving duplicate tweets. I am doing something like that : </p>
  
  <pre class="lang-js prettyprint-override"><code>TweetsModel.find({tweet_id: tweet.tweet_id}, function (err, tweets) {
      if(tweets.length &gt; 0){
          cb('Tweet already exists',null);
      } else{
          tweet.save(function(err){
              cb(err,user);
          });
      }
  });
  </code></pre>
  
  <p>My question is : for performance reason, is there a way using Mongoose to avoid doing two requests ? One find and one save ? </p>
  
  <p>Knowing that I don't want to update the tweet if it already exists either.</p>
  
  <p>Thank you</p>