Lesson 7: Using Query Parameters

In this lesson, you parse the query parameters passed with the REST request, appending the search filters that result to your find operation. As in the previous lesson, you communicate with a MongoDB database. The lesson starts at 3:07:00 of this video, and continues to 5:05:34.

Concept: Thenables

One part of this assignment is a little confusing. You will see code like this:

let result = Product.find(queryObject);
...
result = result.sort(sortList);
...
result = result.select(fieldsList);
...
const products = await result;

How can this work? Isn’t Product.find asynchronous? The reason it works is that Product.find doesn’t return a Promise. It returns something that works like a Promise, but has extended capabilities. This is called a “then-able”. In this case, the thenable allows the search to be further defined. The Product.find call does not immediately send anything to the Mongo database, until await (or .then) is called on the thenable. Only then is the fully qualified search is sent to the database, and the Promise is resolved, and the products found by the search are returned.

Concept: Regular Expressions

Regular expressions provide a general purpose string parsing syntax. A regular expression can be used to identify strings that match a pattern. Regular expressions can also be used to create modified strings by substituting character patterns. There are several tutorials on regular expressions on the web. Here is a selection of them:

• Regex Tutorial
• Game to help learn regex
• Interactive regex exercises

In this course, we will not teach the use of regular expressions, but you should be aware of their purpose. To complete your homework, you can just copy the regular expressions used by the instructor from their location in the final directory.

Continue to work in the node-express-course repository. Create a new branch, week7. This should be created when the week6 branch is active, so that your new work adds to the previous work. You will work in the directory 04-store-api/starter. Once you have changed to that directory, be sure to run npm install to install the required Node modules. As in previous lessons, you will duplicate the work of the instructor, testing as you go with Postman.

This is a difficult lesson, so take your time with it, stopping the video as needed so that you understand what is being done. Also, if you get stuck, the instructor’s solution is in the 04-store-api/final directory. The idea is that one can search by any or all of these attributes: featured, name, price, rating, and company. For the numeric fields (price and rating), one can also specify that you are comparing the number given to see if its “greater than”, “less than”, or “equal to” that value. One can also specify a sort order (ascending or descending). Also, one can specify a skip and a limit, to facilitate pagination through the result. Be sure that you test each step with Postman. Almost all the work will be done in the controllers/product.js file. That file has two methods, getAllProducts and getAllProductsStatic. The getAllProductsStatic method is there for you to experiment with and won’t be directly reviewed.