title: How do I exclude fields from an embedded document in Mongoid?
body: <p>I have a Post document that has embedded tags. Sometimes I display only the title of a post and its tags. In those cases, I use the following query in mongoid:</p>
  
  <pre><code>Post.only(:title).find(id)
  </code></pre>
  
  <p>I then send the results of the query as json to the client. Unfortunately, the tag's bson id makes the json much larger than I need it to be. <strong>How do I exclude the "_id" field from the query?</strong></p>
  
  <p>Here are my models:</p>
  
  <pre><code>class Post
    include Mongoid::Document
    field :title, :type =&gt;  String
    field :body, :type =&gt;  String
    field :tags, :type =&gt;  Array
    embeds_many :tags
  end
  class Tag
    include Mongoid::Document  
    field :tag, :type =&gt;  String
    field :type, :type =&gt;  String
    embedded_in :post
  end
  </code></pre>