title: mongoose query: find an object by id in an array
body: <p>How could I find an image by id in this Schema. I have the id of the User and the id of the image I am looking for. What would be the best way to do this and do all images in this case have different ids or could they have the same id because they don't belong to the same User?</p>
  
  <p>My Schema looks like this:</p>
  
  <pre><code>var userSchema = new Schema({
    local: {
      email: String,
      password: String
    },
    facebook: {
      id: String,
      token: String,
      email: String,
      name: String
    },
    name: String,
    about: String,
    images: [{
      id: Schema.ObjectId,
      link: String,
      main: Boolean
    }]
  });
  </code></pre>