title: has Loopback Model got "exists" method with where clause?
body: <p>I would like to use query the data using filter but only to check whether it exists. </p>
  
  <p>Does loopback support the following way to querying? if yes, can you please share the pointer?</p>
  
  <pre><code>myModel.exists({where: {and: [{city: "London"}, {gender: "F"}]}}, function(err, bool){
   if(bool) callback();
  });
  </code></pre>
  
  <p>Please suggest.</p>
  
  <p>Thanks,</p>