Evolution of a Node.js API, Zoe.js — Request & Response
An API receives requests and gives back responses. This chapter is about Request Encapsulation and Response Transformation.
Request
When I’m working on a code I like to show my intentions explicitly and that’s why Zoe.js has Request objects for creating or updating resources.
Request object
A Request object has 2 goals:
- it shows the entire Request data what is possible
- it validates the entire Request data
Number 1 helps you with understanding and reading the code. With achieving Number 2 you’ll end up a Request object which you can use anywhere in your code, knowing it contains valid data.
For validation requests we’re going to use joi data validator. joi has a simple still powerful schema description language for validating data. Now install joi with:
npm install joiIn order to accomplish a proper validation with joi we need 2 helper classes:
- Validation Error class
- Request validator service class
Validation Error class
When a validation error occurs we can throw this Error class. We’ll use this to build the HTTP Response, json body will contain name and metadata, HTTP status code will be 422.
Request validator service class
Request validator will reduce code duplication as a general service class in our project. It simply validates this._request data based on this._schema and if an error occurs it throws ValidationError.
Product create request
Now we have everything to create our first Request class which is the ProductCreateRequest.
What we see here is that ProductCreateRequest extends our RequestValidator. this._schema contains joi's schema, there's a required minimum 5 chars long string id property, a required minimum 3 chars long name property, and a required positive integer price property. Finally we check the errors and we have getter methods for all the request properties and a buildProductData method which builds a product data object.
In order to be able to fetch the HTTP Response JSON body in the Controller Layer we have to add an Express.js middleware to the app/config/app.js file which parses the incoming JSON request and puts it in to the req.body property.
app.use(express.json())When it’s done we can use our ProductCreateRequest class in the Controller layer.
Additionally I put the logic inside a try...catch block to catch all the exceptions, currently a validation error can occur.
Validation works because there are no id and price properties in the request.
I just complete the product create request body with id and price and now it works like a charm!
(You can check the ProductUpdateRequest class in the source code).
Response
We’re done with the Request part, now we’d like to give back a Response. For giving back a Response we’re going to use Resource classes to be able to Transform the Response as we'd like. Think of a password field what you don't want to expose, or a secret field which needs to be exposed by a specific admin role. Resource class helps you with that.
There is nothing special here, just a plain JS class which stores data. As you can see currently I don’t have any special logic. Let’s use it in our Controller for giving back a Response.
That’s it, now the response has its own body with the product data.
Another option is to add a Location header with the new Resource URL, in that case you don't need a body here.
Source Code
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