title: How to create a subschema in mongoose schema that's not an array
body: <p>I have a mongoose schema with 4 subschemas within it. I been following the documetation here <a href="https://github.com/LearnBoost/mongoose" rel="nofollow">https://github.com/LearnBoost/mongoose</a> on embedded documents</p>
  
  <pre><code>var scenarios = new Schema({
      title: 'String',
      type: 'String',
      description:  'String',
      authorId:  'String',
      categories:  [categoriesSchema],
      subcategories: [subcategories_schema],
      presentation: [presentations_schema],
      scripts: [scripts_schema],
      revision: 'String',
      createDate: 'String',
      updateDate: 'Date',
      active: 'Boolean',
      display:  'Boolean',
      status: [statusSchema],
      video: [video_schema],
      bundleId: [bundleSchema],
      sortOrder: 'Number'
  });
  </code></pre>
  
  <p>My question is for instance if I didn't want presentation to be an array ,and only wanted to allow 1 presentation per scenario would there be a way to handle that on the schema definition?</p>