.NET Middleware & Validation

Introduction

In this challenge you will build an API, write custom middleware and filters that satisfies the requirements listed under the Middleware and Filter Requirements section.

Completion of this project demonstrates working understanding of

• .NET Pipeline
• Middleware
• Action Filters
• Http Context
• Request Validation

Prerequisites

.NET 7 SDK

Instructions

1. Project Setup

• Create a new empty solution and call it whatever you want eg MiddlewareAndValidation. If using .NET CLI Tool use dotnet new sln -n <project_name>.
• Create two new Projects
  • Api: Web API Project, this is where Controllers, Mapping Extension methods and API Contracts will live.
  • Application: Class Library, this is where our Models and Repositories will live along with Extension Methods for project registration.

Create a reference where Api project references the Application project.

If you need help with project creation and referencing using the dotnet cli tool reach out for help or you can also use dotnet --help and dotnet new --help to help figure out the needed commands.

1.a Required NuGet Packages

Application

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

1.b API Contracts

In the Api project create a folder called Contracts and inside of Contracts create two classes

• CreatePostRequest: Represents a incoming request to make a new Post
• UserUpsertRequest: upsert means Update / Insert, this class is used for incoming requests that update or create a user.

These two classes will be used to represent the request body for incoming POST / PUT requests to the API for creating or updating Posts or Users respectively.

1.c Application Registration & In Memory DB Setup

In order to get the Application and In-Memory database setup correctly we will need to do the following...

• Setup repositories

// File: Application/Respositories/UserRepository
public class UserRepository : IUserRepository
{
    // in-memory DB
    private readonly List<User> _users = new();
 
   // your repository methods here...   
}

// File: Application/Repositories/PostRepository
public class PostRepository : IPostRepository
{
    // in-memory DB
    private readonly List<Post> _posts = new();
 
   // your repository methods here...   
}

• Setup Registration File

// File: Application/ApplicationServiceCollectionExtensions
public static class ApplicationServiceCollectionExtensions
{
    public static IServiceCollection AddApplication(this IServiceCollection services)
    {
        services.AddSingleton<IUserRepository, UserRepository>();
        services.AddSingleton<IPostRepository, PostRepository>();
        return services;
    }
}

• Register the Application project

// File: Api/Program.cs
var builder = WebApplication.CreateBuilder(args);

// Other code...

builder.Services.AddApplication();

var app = builder.Build();

Important Note If your application is forcing HTTP requests and giving you odd behavior related to HTTPS you can delete this line here...

var app = builder.Build();

// Other code...

app.UseHttpsRedirection(); // <- remove this line and restart server

Middleware and Filter requirements

• Logger

  • Create a logger middleware that logs to the console the following information about each request in this format:
    • [MiddlewareAndValidationLogger] {request_method} | {request_url} | {timestamp}
  • this middleware runs on every request made to the API

NOTE: To send a response from a filter use the Result property on the ActionExecutingContext object Red on the ActionExecutingContext here for more

• Validate UserId Filter

  • this filter will be used for all user endpoints that include an id parameter in the url (ex: /api/users/:id) and it should check the database to make sure there is a user with that id.
  • if the id parameter is valid, store the user object on HttpContext and allow the request to continue
  • if the id parameter does not match any user id in the database, respond with status 404 and { message: "user not found" }
  • this filter should only be able to be used on Controller Actions.
  • Important Note have your filter inherit from the Attribute Class and implement either IActionFilter or IAsyncActionFilter

• ValidateUser

  • Using Data Annotations validate the body on a request to create or update a user
  • if the request body lacks the required name field, the API should respond with a Validation Error

• Validate Post

  • Using Data Annotations validate the body on a request to create a new post
  • if the request body lacks the required text field, the API should respond with a Validation Error

Repositories (Data Access)

IUserRepository

• CreateAsync: calling CreateAsync passing it a User will add the user to the database and return true when successfully added.
• ExistsAsync: calling ExistsAsync passing in a userID will return a User if the user exists, else returns null.

IPostRepository

• CreateAsync: calling CreateAsync passing it a Post will add the post to the database and return true when successfully added.

All methods should return a Task, when returning use Task.FromResult

Database Schemas

The Database Schemas for the users and posts resources are:

Users

field	data type	metadata
id	Guid	primary key
name	string	required, unique

Posts

field	data type	metadata
id	Guid	primary key
text	text	required
user_id	Guid	required, must be the id of an existing user

Stretch (Optional)

These tasks are less hand held than up above. Tasks vary in level of difficulty. If you would like to implement these requirements, you are going to have to bridge the gap by researching about .NET topics such as Model Binding, Model Validation, ProblemDetailsObject out parameters and other items.

[Routes and Data Access]

You may have noticed this API is not feature complete. Implement missing routes so that full CRUD can be performed on both User and Post resources including getting ALL Posts / Users or finding a User / Post by id. Implement any other functionality needed in the repositories to help support the newly created routes and their functionality.

[Filter] Validate UserId Filter

instead of the filter responding with { message: "user not found } construct a ProblemDetails object Setting the Title to Validation Failed, Status to 400, Instance to the requested URL (this should come from the HTTP Context) Add the key userId and error of user with the provided id does not exist

[IUserRepository Method] ExistsAsync

Create a overload of ExistsAsync, that accepts two values a userId and a out parameter for the user your out parameter should be of type User? (nullable user). If a user exists return true and assign the out paramter to the found user. Else return false, and assign the user out parameter to be null

[Mapping Layer]

In the Api project create a folder called Mapping with static classes of UserMapping and PostMapping in these classes you will create extension methods that converts types declared in Contracts (created in step 1.b) to types that are defined in Application.Models respectively. You will want a way to map from Contracts -> Models and back from Models -> Contracts. Your controllers are responsible for taking in a contract and converting it to a model before calling on database actions and converting models back into contracts when sending out a response.

[Validation using Fluent Validation]

In the Api project, we have our Contracts. Our contracts were to be validated using Data Annotations. Pick one of the contracts either UpsertUserRequest or CreatePostRequest and remove the data annotation(s).

Install the NuGet Package FluentValidation.DependencyInjectionExtensions to the Api project

In Api project create a new folder called Validators and create a class called UpsertUserValidator and write the needed logic for validating the required field on the incoming request.

Create a new interface under Api project called IApiAssemblyMarker and use it to register all validators in the Api assembly.

From there, create a new filter called UpsertUserActionFilter and preform the needed validation on the incoming request.

• If validation is in a failed state respond with a ProblemDetailsObject. Setting the Title to Validation Failed, Status to 400, Instance to the requested URL (this should come from the HTTP Context). The key and value used here is going to be dynamic and come from the validation result generated using your UpsertUserValidator.

• If validation is in a success state, then call on the next method in the pipeline.