title: mongo store document meta data
body: <p>Which is the best way to store meta data for a document, in the document itself or in separate collection?</p>
  
  <p>I am working with a collection that has data like this:</p>
  
  <pre><code>{
     status: {
         joined: Date,
         retired: [{
             on: Date,
             comment: String,
             reinstated: {
                 on: Date,
                 comment: String
             }
         }],
         suspended: [{
             on: Date,
             comment: String,
             reinstated: {
                 on: Date,
                 comment: String
             }
         }],
         //.....
  </code></pre>
  
  <p>I need to keep a log of when and who performs these changes, but I am not sure if I should add the metadata to each element or have a collection like Log.</p>
  
  <pre><code>// Log collection
  {
      by: UserId,
      on: Date,
      verb: String,
      object: ObjectId,
      comment: String
  }
  </code></pre>