title: Initializing a ref array in Mongoose
body: <p>Say I have the following schemas:</p>
  
  <pre><code>var promoGroupSchema = new Schema({
      title: String,
      offers: [{Schema.Types.ObjectId, ref: 'Offer']
  });
  </code></pre>
  
  <p>and</p>
  
  <pre><code>var offerSchema = new Schema({
      type: String
  });
  </code></pre>
  
  <p>How do you initialize a promoGroup with new offers? The following won't work since save() is asynchronous. Now, I know I could put a function as a parameter of the save function, but that gets ugly with more offers.</p>
  
  <pre><code>var offer1 = new offerSchema({
      type: "free bananas!"
  });
  
  var offer2 = new offerSchema({
      type: "free apples!"
  });
  
  offer1.save();
  offer2.save();
  
  var newPromoGroup = new promoGroupSchema({
      title: "Some title here",
      offers: [offer1._id, offer2._id]
  });
  </code></pre>
  
  <p>From what I read, Mongoose gives the object an _id as soon as you create them, can I rely on those?</p>