title: Why does Mongoose hide my field?
body: <p>Mongoose seems to be hiding my timestamp field when I'm setting it in a pre 'save' hook. Any idea why?</p>
  
  <p>I have this Schema:</p>
  
  <pre><code>var dpsSchema = new Schema({
      timestamp: Date,
      _loaded_schedules: [{type: Number, ref: 'prun_schedules'}]
  })
  
  dpsSchema.pre('save', function(next){
      this.timestamp = new Date();
      next();
  })
  </code></pre>
  
  <p>and I run this code:</p>
  
  <pre><code>var Dpm_model = mongoose.model('daily_production_meta', dpm_schema);
  
  var pm = new Dpm_model();
  pm.save();
  
  setTimeout(console.log(pm), 2000);
  </code></pre>
  
  <p>The resulting console log looks like this:</p>
  
  <pre><code>{ _id: 5871410c08b91cfd82124656,
    _loaded_schedules: [] }
  </code></pre>
  
  <p>But when I log into mongodb via terminal and check that document, I see the timestamp field!</p>
  
  <p>How come?</p>