Creating a user-defined model around a Mongoose model

After seeing how a model works, it is time to create a user-defined module that wraps all CRUD operations for the catalog. Since we intend to use that module in a RESTful web application, it seems logical to leave the schema definition and the model creation outside the module and have them provided as arguments of each module function. The same schema definition is used in the unit tests, ensuring stability of the module. Now let's add an implementation for each CRUD function, starting with a remove() function. It looks up an item based on its id and deletes it from the database, if it exists:

exports.remove = function (request, response) {
  console.log('Deleting item with id: '    + request.body.itemId);
  CatalogItem.findOne({itemId: request.params.itemId}, function(error, data) {
      if (error) {
        ...