js/libs/ember-data.js
function(hash) {
    var owner = get(this, 'owner'),
        store = get(owner, 'store'),
        type = get(this, 'type'),
        record;

    Ember.assert("You cannot add '" + type.typeKey + "' records to this polymorphic relationship.", !get(this, 'isPolymorphic'));

    record = store.createRecord.call(store, type, hash);
    this.pushObject(record);

    return record;
  }
function(hash) {
    var owner = get(this, 'owner'),
        store = get(owner, 'store'),
        type = get(this, 'type'),
        record;

    Ember.assert("You cannot add '" + type.typeKey + "' records to this polymorphic relationship.", !get(this, 'isPolymorphic'));

    record = store.createRecord.call(store, type, hash);
    this.pushObject(record);

    return record;
  }
Create a child record within the owner

@method createRecord
@private
@param {Object} hash
@return {DS.Model} record