Changing buildURL according to the record type.

application.js

 createRecord: function(store, type, record) {
    var data = {};
    var serializer = store.serializerFor(type.typeKey);

    serializer.serializeIntoHash(data, type, record, { includeId: true });
    if (record.get('isNew') && type.typeKey == 'room' && data.room.operation_id)
    {
      var op_id = data.room.operation_id;
      delete data.room.operation_id;
      return this.ajax(this.buildURL('operations/' + op_id + '/room', null, record), "POST", { data: data });
    } else {
      return this.ajax(this.buildURL(type.typeKey, null, record), "POST", { data: data });
    }