title: Mongoose Async Issues
body: <p>let's say I have this Schema:</p>
  
  <pre><code>var PersonSchema = new Schema({
  name: Schema.Types.Mixed,
  idRdv:{type:Schema.Types.ObjectId, ref: 'Rdv'}
  });
  </code></pre>
  
  <p>And another Schema:</p>
  
  <pre><code>var RdvSchema = new Schema({
  _idRdv:{type: Schema.Types.ObjectId},
  person:{type: Schema.Types.Mixed, ref:'Person'}
  });
  
  var Person= mongoose.model('Person', PersonSchema);
  var Rdv = mongoose.model('Rdv',RdvSchema);
  </code></pre>
  
  <p>When I add datas:</p>
  
  <pre><code>var person1= new Person({
  Name: 'Jean',
  _idRdv: rdv1._idRdv &lt;--- this value isn't defined yet so it won't pass it to mongo
  
  var rdv1 = new Rdv({
  _idRdv: new mongoose.Types.ObjectId(),
  person: person1.Name
  });
  </code></pre>
  
  <p>When I add datas to these Schemas I'll have a problem with patient not receiving the _idRdv value since patient has been created before Rdv.</p>
  
  <p>Is there a way to make it possible to have the _idRdv filled too ?</p>