.NET Server Side Routing and Data Repositories

Introduction

Use .NET to build an API that performs CRUD operations on blog posts. Completion of this exercise shows demonstration and understanding of...

• Repository Pattern
• Use of .NET Dependency Injection
• Library registration using IServiceCollection
• Extension Methods
• Modeling Requests, Responses and Domain level data
• Controller based routing
• Mapping pattern converting between domain and external representation of data

Prerequisites

.NET 7 SDK

Instructions

Project Setup

Create a new solution in the project root using dotnet new sln -n <solution_name> replacing <solution_name> with the name of the project like PostsService.

Create two new projects

• Posts.Api: Web API Project, this is where Controllers, Mapping Extension methods and API Contracts will live.
• Posts.Application: Class Library, this is where our Models and Repositories will live along with Extension Methods for project registration.

Create a project reference where Posts.Api refers to Posts.Application

Posts.Application Nuget Packages

• Microsoft.Extensions.DependencyInjection.Abstractions: required for being able to register the Posts.Application properly

Task 1: Minimum Viable Product

• Add the code necessary to Posts.Api and Posts.Application to implement the endpoints listed below.

• Configure the API to handle to the following routes. Some of these endpoints might require more than one call to the Post repository in Post.Application/Repositories/Post.cs.

N	Method	Endpoint	Description
1	GET	/api/posts	Returns an array of all the post objects contained in the database
2	GET	/api/posts/:id	Returns the post object with the specified id
3	POST	/api/posts	Creates a post using the information sent inside the request body and returns the newly created post object
4	PUT	/api/posts/:id	Updates the post with the specified id using data from the request body and returns the modified document, not the original
5	DELETE	/api/posts/:id	Removes the post with the specified id and returns the deleted post object
6	GET	/api/posts/:id/comments	Returns an array of all the comment objects associated with the post with the specified id

2 [GET] /api/posts/:id

• If the post with the specified id is not found:

  • return HTTP status code 404 (Not Found).
  • return the following JSON: { message: "The post with the specified ID does not exist" }.

3 [POST] /api/posts

• save the new post the the database.
• return HTTP status code 201 (Created).
• return the newly created post.

4 [PUT] /api/posts/:id

• If the post with the specified id is not found:

  • return HTTP status code 404 (Not Found).
  • return the following JSON: { message: "The post with the specified ID does not exist" }.

• If the post is found:

  • update the post using the new information sent in the request body.
  • return HTTP status code 200 (OK).
  • return the newly updated post.

5 [DELETE] /api/posts/:id

• If the post with the specified id is not found:

  • return HTTP status code 404 (Not Found).
  • return the following JSON: { message: "The post with the specified ID does not exist" }.

6 [GET] /api/posts/:id/comments

• If the post with the specified id is not found:

  • return HTTP status code 404 (Not Found).
  • return the following JSON: { message: "The post with the specified ID does not exist" }.

Repository API

In the Posts.Application class library create a folder called Repositories, in the Repositories folder create a IPostRepository interface and also a PostRepository class.

The IPostRepository should declare the following methods...

• InitDb: Returns a Task of type boolean and will setup dummy data in the PostRepository. More on this in the Important Notes section
• GetAllAsync: Returns a Task of IEnumerable of type Post, that will get all posts contained in the in-memory DB
• CreateAsync: calling CreateAsync and providing a domain Post object will add a post to the in-memory DB that returns a Task of type boolean indicating the post was successfully added.
• UpdateAsync: calling UpdateAsync and providing a domain Post object will update a post in the in-memory DB that returns a Task of type boolean indicating the post was successfully updated.
• GetByIdAsync: takes a id as input that represents a post id returning a Task of type Post where post is a post matching the provided id or null if a post with the provided id does not exist
• DeleteByIdAsync: takes a id as input that represents a post id returning a Task of type boolean returning true if a post was removed or false if there was no item to be deleted
• GetCommentsByPostIdAsync: to find Comments associated to a Post, take in a Post Id and get all comments where the comment Post Id matches the provided post id returning a Task of type IEnumerable of type Comment

The PostRepository should then implement the IPostRepository, and then added to the .NET Dependency Injection container example of this in the Important Notes section.

Blog Post Schema

A Blog Post in the database has the following structure:

{
  id: "9d9ecdbf-cad0-4111-a688-b7d796bf31d1", // Guid, required
  title: "The post title", // String, required
  contents: "The post contents", // String, required
  created_at: Mon Aug 14 2017 12:50:16 GMT-0700 (PDT) // DateTime, defaults to current date and time
  updated_at: Mon Aug 14 2017 12:50:16 GMT-0700 (PDT) // DateTime, defaults to current date and time
}

Comment Schema

A Comment in the database has the following structure:

{
  text: "The text of the comment", // String, required
  post_id: "The id of the associated post", // Integer, required, must match the id of a post entry in the database
  created_at: Mon Aug 14 2017 12:50:16 GMT-0700 (PDT) // Date, defaults to current date
  updated_at: Mon Aug 14 2017 12:50:16 GMT-0700 (PDT) // Date, defaults to current date
}

Important Notes

Disable Https Locally

You can run into some strange behavior locally when using Https so we can disable it

// Program.cs
var app = builder.Build();

// Other items...

// Disable HTTPs locally
if (!app.Environment.IsDevelopment())
{
    app.UseHttpsRedirection();
}

Add Application and Init In-Memory DB

In order to get the Posts.Application in-memory database setup correctly we will need to do the following...

• Setup the repository class

// Posts.Application/Repositories/PostRepository.cs
public class PostRepository
{
    // in memory DB
    private readonly List<Post> _posts = new();
    private readonly List<Comment> _comments = new();

    public Task<bool> InitDb()
    {
        var p = new Post
        {
            Id = Guid.NewGuid(),
            Title = ".NET Is The Best",
            Contents = ".Net is the best...that is all",
            CreatedAt = DateTime.UtcNow,
            UpdatedAt = DateTime.UtcNow
        };

        var c = new Comment
        {
            CommentId = Guid.NewGuid(),
            Text = "This was awesome!",
            PostId = p.Id
        };
        
        _posts.Add(p);
        _comments.Add(c);
        
        return Task.FromResult(true);
    }
}

• Setup an extension method to run InitDb

using Microsoft.Extensions.DependencyInjection;
using Posts.Application.Repositories;

// Posts.ApplicationServiceCollectionExtensions
public static class ApplicationServiceCollectionExtensions
{
    public static IServiceCollection AddApplication(this IServiceCollection services)
    {
        services.AddSingleton<IPostRepository, PostRepository>();
        return services;
    }

    public static IServiceProvider AddDatabase(this IServiceProvider services)
    {
        var repository = services.GetRequiredService<IPostRepository>();
        repository.InitDb();

        return services;
    }
}

• Register the Post.Application project and add the DB

// Program.cs

var builder = WebApplication.CreateBuilder(args);

// Other code...

// Custom Registration
builder.Services.AddApplication();

var app = builder.Build();

// Init in-memory DB
app.Services.AddDatabase();