backend_structure.md

Backend Structure

The backend of this project can be found in the api directory.

It consists of a few parts. This page will go some way to explain the different parts, and how they fit together.

Contents

• main.go
• app.js
• routes
• controllers
• models
• middleware
• lib
• db

main.go

This is the file we run when we want to start our server. It does two things:

1. Connect to the Postgresql database.
2. Creates our application
   1. Configures CORS settings.
   2. Sets up our api routes at /users, /posts and /tokens
3. Start our app, listening for incoming HTTP requests.

routes

Our routes define the different request URLs that our api will respond to. They also define which controllers will handle which requests. Each file in the routes directory defines one route, with multiple endpoints.

For example, posts.go creates two routes:

• POST <BACKEND_URL>/posts to create a new post with controllers.CreatePost
• GET <BACKEND_URL>/posts to get all posts with controllers.GetAllPosts

controllers

Controllers contain the functions that actually handle the requests that our app recieves. Each controller is a function that takes one argument, the Gin context. This struct has information about the request, and methods and fields we can use to send a response.

The full list of features can be found here.

We can also add data to the ctx struct with middleware, such as the AuthenticationMiddleware adding the user_id property, which can then be used by controller functions.

We can respond to requests using the ctx.JSON method to send a JSON string.

models

Our models are structs that handle interaction with the database. We create our models using a library called Gorm. Each model is created with a declaration, which defines the shape of the data in the database, ie. what fields the entries in our database have.

These structs provide built-in methods, such as .First, .Last and .Find. More info can be found here.

To create entries in the database, we create a struct, and use the .Save function:

	testPost := models.Post{
		Message: fmt.Sprintf("This is a test message created at %v!", time.Now()),
	}
	testPost.Save()

middleware

Middleware are similar to our controller handler functions, but don't necessarily end with a response. Instead they call a next method to pass on to the next handler.

For example, the AuthenticationMiddleware makes sure that the request has been sent with a vaild token. If it has, it passes on to the next handler, such as the posts router. If it has an invalid token, it will send an error response back to the client.

auth

The lib directory simply contains functions which can be used from anywhere in our app, for handling authentication.

env

This is a small package for loading environment variables.