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CommandQuery.AspNetCore 馃寪

build CodeFactor

Command Query Separation for ASP.NET Core

  • Provides generic actions for handling the execution of commands and queries
  • Enables APIs based on HTTP POST and GET

Get Started

  1. Create a new ASP.NET Core project
  2. Install the CommandQuery.AspNetCore package from NuGet
    • PM> Install-Package CommandQuery.AspNetCore
  3. Create commands and command handlers
    • Implement ICommand and ICommandHandler<in TCommand>
    • Or ICommand<TResult> and ICommandHandler<in TCommand, TResult>
  4. Create queries and query handlers
    • Implement IQuery<TResult> and IQueryHandler<in TQuery, TResult>
  5. Configure services in Startup.cs

Add a new project - ASP.NET Core Web API

Choose:

  • .NET 6.0 (Long Term Support)
  • Use controllers (uncheck to use minimal APIs)

Configuration

Configuration in Program.cs:

using CommandQuery;
using CommandQuery.AspNetCore;
using CommandQuery.Sample.Contracts.Commands;
using CommandQuery.Sample.Contracts.Queries;
using CommandQuery.Sample.Handlers;
using CommandQuery.Sample.Handlers.Commands;
using CommandQuery.Sample.Handlers.Queries;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

// Add commands and queries
builder.Services.AddCommandControllers(typeof(FooCommandHandler).Assembly, typeof(FooCommand).Assembly);
builder.Services.AddQueryControllers(typeof(BarQueryHandler).Assembly, typeof(BarQuery).Assembly);

// Add handler dependencies
builder.Services.AddTransient<IDateTimeProxy, DateTimeProxy>();
builder.Services.AddTransient<ICultureService, CultureService>();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

// Validation
app.Services.GetService<ICommandProcessor>()!.AssertConfigurationIsValid();
app.Services.GetService<IQueryProcessor>()!.AssertConfigurationIsValid();

app.Run();

The extension methods AddCommandControllers and AddQueryControllers will add controllers and all command/query handlers in the given assemblies to the IoC container. You can pass in a params array of Assembly arguments if your handlers are located in different projects. If you only have one project you can use typeof(Startup).Assembly as a single argument.

Commands

The action method from the generated controller will handle commands:

/// <summary>
/// Handle a command.
/// </summary>
/// <param name="command">The command.</param>
/// <param name="cancellationToken">A cancellation token that can be used by other objects or threads to receive notice of cancellation.</param>
/// <returns>The result for status code <c>200</c>, or an error for status code <c>400</c> and <c>500</c>.</returns>
[HttpPost]
public async Task<IActionResult> HandleAsync(TCommand command, CancellationToken cancellationToken)
  • The action is requested via HTTP POST with the Content-Type application/json in the header
  • The name of the command is the slug of the URL
  • The command itself is provided as JSON in the body
  • If the command succeeds; the response is empty with the HTTP status code 200
  • If the command fails; the response is an error message with the HTTP status code 400 or 500

Commands with result:

/// <summary>
/// Handle a command.
/// </summary>
/// <param name="command">The command.</param>
/// <param name="cancellationToken">A cancellation token that can be used by other objects or threads to receive notice of cancellation.</param>
/// <returns>The result for status code <c>200</c>, or an error for status code <c>400</c> and <c>500</c>.</returns>
[HttpPost]
public async Task<IActionResult> HandleAsync(TCommand command, CancellationToken cancellationToken)
  • If the command succeeds; the response is the result as JSON with the HTTP status code 200.
  • If the command fails; the response is an error message with the HTTP status code 400 or 500.

Queries

The action methods from the generated controller will handle queries:

/// <summary>
/// Handle a query.
/// </summary>
/// <param name="query">The query.</param>
/// <param name="cancellationToken">A cancellation token that can be used by other objects or threads to receive notice of cancellation.</param>
/// <returns>The result + 200, 400 or 500.</returns>
[HttpPost]
public async Task<IActionResult> HandlePostAsync(TQuery query, CancellationToken cancellationToken)
/// <summary>
/// Handle a query.
/// </summary>
/// <param name="query">The query.</param>
/// <param name="cancellationToken">A cancellation token that can be used by other objects or threads to receive notice of cancellation.</param>
/// <returns>The result + 200, 400 or 500.</returns>
[HttpGet]
public async Task<IActionResult> HandleGetAsync([FromQuery] TQuery query, CancellationToken cancellationToken)
  • The action is requested via:
    • HTTP POST with the Content-Type application/json in the header and the query itself as JSON in the body
    • HTTP GET and the query itself as query string parameters in the URL
  • The name of the query is the slug of the URL.
  • If the query succeeds; the response is the result as JSON with the HTTP status code 200.
  • If the query fails; the response is an error message with the HTTP status code 400 or 500.

Testing

You can integration test your controllers and command/query handlers with the Microsoft.AspNetCore.Mvc.Testing package.

using System.Net;
using System.Text;
using CommandQuery.Sample.Contracts.Queries;
using FluentAssertions;
using Microsoft.AspNetCore.Mvc.Testing;
using NUnit.Framework;

namespace CommandQuery.Sample.AspNetCore.V6.Tests
{
    public class QueryControllerTests
    {
        public class when_using_the_real_controller_via_Post
        {
            [SetUp]
            public void SetUp()
            {
                Factory = new WebApplicationFactory<Program>();
                Client = Factory.CreateClient();
            }

            [TearDown]
            public void TearDown()
            {
                Client.Dispose();
                Factory.Dispose();
            }

            [Test]
            public async Task should_work()
            {
                var content = new StringContent("{ \"Id\": 1 }", Encoding.UTF8, "application/json");

                var result = await Client.PostAsync("/api/query/BarQuery", content);
                var value = await result.Content.ReadAsAsync<Bar>();

                result.EnsureSuccessStatusCode();
                value.Id.Should().Be(1);
                value.Value.Should().NotBeEmpty();
            }

            [Test]
            public async Task should_handle_errors()
            {
                var content = new StringContent("{ \"Id\": 1 }", Encoding.UTF8, "application/json");

                var result = await Client.PostAsync("/api/query/FailQuery", content);

                result.StatusCode.Should().Be(HttpStatusCode.NotFound);
                (await result.Content.ReadAsStringAsync()).Should().BeEmpty();
            }

            WebApplicationFactory<Program> Factory;
            HttpClient Client;
        }

        public class when_using_the_real_controller_via_Get
        {
            [SetUp]
            public void SetUp()
            {
                Factory = new WebApplicationFactory<Program>();
                Client = Factory.CreateClient();
            }

            [TearDown]
            public void TearDown()
            {
                Client.Dispose();
                Factory.Dispose();
            }

            [Test]
            public async Task should_work()
            {
                var result = await Client.GetAsync("/api/query/BarQuery?Id=1");
                var value = await result.Content.ReadAsAsync<Bar>();

                result.EnsureSuccessStatusCode();
                value.Id.Should().Be(1);
                value.Value.Should().NotBeEmpty();
            }

            [Test]
            public async Task should_handle_errors()
            {
                var result = await Client.GetAsync("/api/query/FailQuery?Id=1");

                result.StatusCode.Should().Be(HttpStatusCode.NotFound);
                (await result.Content.ReadAsStringAsync()).Should().BeEmpty();
            }

            WebApplicationFactory<Program> Factory;
            HttpClient Client;
        }
    }
}

Samples