title: How to define mongoose schema inside shcema
body: <p>Here is an example:</p>
  
  <pre><code>    var aaaSchema = new mongoose.Schema({
          name: String,
      });
  
      var testSchema = new mongoose.Schema({
          test: mongoose.Schema.Types.Mixed,
      });
  </code></pre>
  
  <p>For now, test could be any Object since it is: mongoose.Schema.Types.Mixed
  I want to define test is:</p>
  
  <pre><code>   {
         aa: aaaSchema,
         bb: aaaSchema,
         ....
      }
  </code></pre>
  
  <p>It means that the key could be any string (aa, bb, or others), the value must be {name: String} which is aaaSchema.</p>