Developing a Basic REST API from Scratch Using TDD

Valeri KarpovNode.js Engineer, MongoDBwww.thecodebarbarian.com

github.com/vkarpov15@code_barbarian

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What is this talk about?

•MongoDB is great for storing web/mobile app data•So let’s build a REST API using Node.js!•+ learn a bit about test-driven dev with Node.js•+ learn two MongoDB schema design principles•Server-side only - just JSON, no HTML•No AngularJS part, focus more on MongoDB•Upcoming EdX course

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Overview

•Part 1: Shopping Cart Application–Search for products–Add them to your cart–Check out with Stripe

•Part 2: Using the Mongoose ODM•Part 3: Schema Design•Part 4: Building an API with the Express framework•Part 5: Testing with Mocha + Superagent

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Part 1: What Does the App Do?

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What Does the App Do?

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What Does the App Do?

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App Structure

•"Bad programmers worry about the code. Good programmers worry about data structures and their relationships." - Linus Torvalds•3 schemas for 3 collections:•Products•Categories•Users

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Schema Relationships

•Product belongs to one or more categories•Users can have multiple products in their cart•Representing relationships in MongoDB is tricky•But that’s what mongoose is for

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Part 2: Using the Mongoose ODM•“Object document mapper” (like ORM, but for MongoDB)•“MongoDB object modeling designed to work in an asynchronous environment”•Written for Node.js•Provides schema validation, pseudo-JOINs, etc.

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Brief Overview of Node.js

•require()

•Async I/O

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What Does Async Mean?

Register eventhandler

In node.js, you don’t execute I/O imperatively.You register a callback to execute when the I/O is done

Prints before“done reading”

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Your First Mongoose Schema

matches X@Y.Z

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Using Your Schema

Create User

Save user to MongoDB

Load user from MongoDB

Print user to stdout

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Part 2 Takeaways

•Mongoose provides several neat features–Model part of MVC–Default values–Schema validation and declarative schema design

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Part 3: Schema Design

•3 schemas:–Product–Category–User

•Going to use mongoose to define schemas•Will use a couple key schema design principles

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Product Schema

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Product Schema in Action

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Category Schema

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Category Schema Queries

•What categories are descendants of “Electronics”?•

•What categories are children of “Non-Fiction”?• •What categories are ancestors of “Phones”?

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Product + Category Schemas

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Category Schema Takeaways

•Queries in MongoDB should be simple•Strive for minimal data transformation by server•“Store what you query for”•“If you need [the aggregation framework in a heavily used API endpoint], you're screwed anyway, and should fix your program.” - Linus Torvalds•Good for performance and developer sanity

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User Schema

User’s cart as an arrayof ObjectIds...

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Principle of Least Cardinality

•Product and user = many-to-many relationship•Don’t necessarily need a mapping table•User won’t have 1000s of products in cart•Can represent relationship as array in user since one side is small•If one side of many-to-many is bounded and/or small, it is a good candidate for embedding•Arrays that grow without bound are an antipattern!

–16mb document size limit–network overhead

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Part 4: The Express Framework

•Most popular Node.js web framework•Simple, pluggable, and fast•Great tool for building REST APIs

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Your First Express App

Route Parameter

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What is REST?

•Representational State Transfer•HTTP request -> JSON HTTP response•Business logic on top of MongoDB schemas

–Access control, emails, analytics, etc.

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Structuring Your REST API

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GET /category/id/:idFind Category

Error handling

Output JSON

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GET /category/parent/:id

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GET /product/category/:id

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Adding Products to User’s Cart

•Recall cart is an array of products

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Adding Products to User’s Cart

Get cart from HTTP request

Overwrite user’s cart

Let mongoose handlecasting and validating data

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PUT /me/cart Takeaways

•Mongoose lets you be lazy•Access control using subdocs

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Bonus: Stripe Checkout

Create a Stripe charge with the npm ‘stripe’ module

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Bonus: Stripe Checkout

Error handling

Empty user carton success

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Part 4 Takeaways

•Express REST API on top of mongoose–Access control–Business logic–Define what operations user can take on database

•Mongoose casting and validation for APIs

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Part 5: Test-Driven Development•Building an API is tricky•Lots of different error conditions•Express has a lot of magic under the hood

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NodeJS Concurrency and Testing•Node.js runs in an event loop•Single threaded•Can run client and server on same thread!

–Client sends HTTP request–Client registers a callback awaiting the result–Server’s “on HTTP request” event handler is triggered

–Server sends response, continues waiting for events

–Client’s callback gets fired•Test server end-to-end

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Superagent

•NodeJS HTTP client•Isomorphic: runs in both browser and NodeJS•Same author as Express

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Mocha

•Testing Framework for NodeJS•Same author as Express•BDD-style syntax

–describe() -> test suite–it() -> individual test

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Setting Up Category API Tests

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Testing GET /category/id/:id

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Part 5 Takeaways

•NodeJS concurrency makes testing easy•Not just unit tests - full E2E for your REST API•Can manipulate database and make arbitrary HTTP requests

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•Upcoming EdX Video Course•Slides on http://www.slideshare.net/vkarpov15•Looking for beta testers! Sign up for notifications

–http://goo.gl/forms/0ckaJ4YvJN•Interested in learning about AngularJS?

–Professional AngularJS on Amazon•More NodeJS+MongoDB content at:

–www.thecodebarbarian.com–Twitter: @code_barbarian

Thanks for Listening!