title: How to find by nested property in mongoose
body: <p>I'm trying to find an object in my database by a nested property, I can't seem to find any way to do it. My schema is below and I have shown how I've attempted to query.</p>
  
  <pre><code>var stations = {
      Alpha: Number,
      Beta: Number
  };
  var systemSchema = new mongoose.Schema({
      name: String,
      location: String,
      nodes: {
          main: stations,
          secondary: stations,
          tertiary: stations
      }
  });
  
  var System = mongoose.model("System", systemSchema);
  
  System.findOne({ nodes: { main: {Alpha: 23000}}}, function(err, system){
      if(err){console.log(err);}
      else{console.log(system);}
  });
  </code></pre>
  
  <p>Every time I run this, nothing gets returned. I was expecting that I would have the corresponding object in my database returned. </p>