Default Nested Collection in Mongoose with Node

I'm building an app with Node and MongoDB and I have a company model and an API key model that look like this in Mongoose:

  var APIKeysSchema = new Schema({
    name: { type: String }
  });

  var CompanySchema = new Schema({
      name            : {type : String, required: true, index: { unique: true }}
    , apiKeys           : [ APIKeysSchema ]
    , created_at      : {type : Date, default : Date.now}
  });

I'd like every company to have by default one API key generated when the company is created. Should I write custom middleware for this, or is there some way to do it within the schema itself. Thanks!

Ended up just doing it as middleware on save in the model:

CompanySchema.pre('save', function(next){
    if(this.get('apiKeys').length < 1){
        //generate API key
        var objectId = new ObjectID();
        this.get('apiKeys').push({ key: objectId.toHexString() });
    }
    next();
  });