CommandQuery.AspNet.WebApi 🌐

Command Query Separation for ASP.NET Web API 2

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

Get Started

Create a new ASP.NET Web API 2 project
- Tutorial
Install the CommandQuery.AspNet.WebApi package from NuGet
- PM> Install-Package CommandQuery.AspNet.WebApi
Create controllers
- Inherit from BaseCommandController and BaseQueryController
Create commands and command handlers
- Implement ICommand and ICommandHandler<in TCommand>
- Or ICommand<TResult> and ICommandHandler<in TCommand, TResult>
Create queries and query handlers
- Implement IQuery<TResult> and IQueryHandler<in TQuery, TResult>
Configure dependency injection

Commands

Add a CommandController:

using System.Web.Http;
using System.Web.Http.Tracing;
using CommandQuery.AspNet.WebApi;

namespace CommandQuery.Sample.AspNet.WebApi.Controllers
{
    [RoutePrefix("api/command")]
    public class CommandController : BaseCommandController
    {
        public CommandController(ICommandProcessor commandProcessor, ITraceWriter logger) : base(commandProcessor, logger)
        {
        }
    }
}

Inherit from BaseCommandController and pass the ICommandProcessor to the base constructor.

The action method from the base class will handle all commands:

/// <summary>
/// Handle a command.
/// </summary>
/// <param name="commandName">The name of the command</param>
/// <param name="json">The JSON representation of the command</param>
/// <returns>200, 400 or 500</returns>
[HttpPost]
[Route("{commandName}")]
public async Task<IHttpActionResult> Handle(string commandName, [FromBody] Newtonsoft.Json.Linq.JObject json)

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:

If the command succeeds; the response is the result as JSON with the HTTP status code 200.

Queries

Add a QueryController:

using System.Web.Http;
using System.Web.Http.Tracing;
using CommandQuery.AspNet.WebApi;

namespace CommandQuery.Sample.AspNet.WebApi.Controllers
{
    [RoutePrefix("api/query")]
    public class QueryController : BaseQueryController
    {
        public QueryController(IQueryProcessor queryProcessor, ITraceWriter logger) : base(queryProcessor, logger)
        {
        }
    }
}

Inherit from BaseQueryController and pass the IQueryProcessor to the base constructor.

The action methods from the base class will handle all queries:

/// <summary>
/// Handle a query.
/// </summary>
/// <param name="queryName">The name of the query</param>
/// <param name="json">The JSON representation of the query</param>
/// <returns>The result + 200, 400 or 500</returns>
[HttpPost]
[Route("{queryName}")]
public async Task<IHttpActionResult> HandlePost(string queryName, [FromBody] Newtonsoft.Json.Linq.JObject json)

/// <summary>
/// Handle a query.
/// </summary>
/// <param name="queryName">The name of the query</param>
/// <returns>The result + 200, 400 or 500</returns>
[HttpGet]
[Route("{queryName}")]
public async Task<IHttpActionResult> HandleGet(string queryName)

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.

Configuration

Configuration in App_Start/WebApiConfig.cs

using System.Net.Http.Formatting;
using System.Web.Http;
using System.Web.Http.Tracing;
using CommandQuery.AspNet.WebApi;
using CommandQuery.DependencyInjection;
using CommandQuery.Sample.AspNet.WebApi.Handlers;
using Microsoft.Extensions.DependencyInjection;

namespace CommandQuery.Sample.AspNet.WebApi
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // IoC
            var services = new ServiceCollection();

            services.AddCommands(typeof(WebApiConfig).Assembly);
            services.AddQueries(typeof(WebApiConfig).Assembly);

            services.AddTransient<ICultureService, CultureService>();
            services.AddTransient<IDateTimeProxy, DateTimeProxy>();

            services.AddTransient<ITraceWriter>(_ => config.EnableSystemDiagnosticsTracing()); // Logging

            config.DependencyResolver = new CommandQueryDependencyResolver(services);

            // Web API routes
            config.MapHttpAttributeRoutes(new CommandQueryDirectRouteProvider());

            // Json
            config.Formatters.Clear();
            config.Formatters.Add(new JsonMediaTypeFormatter());
        }
    }
}

The extension methods AddCommands and AddQueries will add 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(WebApiConfig).Assembly as a single argument.

To enable logging, inject an ITraceWriter to the constructor of the controllers.

The CommandQueryDependencyResolver will manage the dependency injection when controllers are created.

The CommandQueryDirectRouteProvider makes sure the routes from the base controllers are inherited.

Consider to clear the default formatters and only use the JsonMediaTypeFormatter.

Testing

You can unit test your controllers and command/query handlers.

using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using System.Web.Http;
using CommandQuery.Sample.AspNet.WebApi.Contracts.Queries;
using CommandQuery.Sample.AspNet.WebApi.Controllers;
using FluentAssertions;
using Newtonsoft.Json.Linq;
using NUnit.Framework;

namespace CommandQuery.Sample.AspNet.WebApi.Tests
{
    public class QueryControllerTests
    {
        public class when_using_the_real_controller_via_Post
        {
            [SetUp]
            public void SetUp()
            {
                var configuration = new HttpConfiguration();
                WebApiConfig.Register(configuration);

                var queryProcessor = configuration.DependencyResolver.GetService(typeof(IQueryProcessor)) as IQueryProcessor;

                Subject = new QueryController(queryProcessor, null)
                {
                    Request = new HttpRequestMessage(),
                    Configuration = configuration
                };
            }

            [Test]
            public async Task should_work()
            {
                var json = JObject.Parse("{ 'Id': 1 }");
                var result = await (await Subject.HandlePost("BarQuery", json)).ExecuteAsync(CancellationToken.None);
                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 json = JObject.Parse("{ 'Id': 1 }");
                var result = await Subject.HandlePost("FailQuery", json);

                await result.ShouldBeErrorAsync("The query type 'FailQuery' could not be found");
            }

            QueryController Subject;
        }

        public class when_using_the_real_controller_via_Get
        {
            [SetUp]
            public void SetUp()
            {
                var configuration = new HttpConfiguration();
                WebApiConfig.Register(configuration);

                var queryProcessor = configuration.DependencyResolver.GetService(typeof(IQueryProcessor)) as IQueryProcessor;

                Subject = new QueryController(queryProcessor, null)
                {
                    Request = new HttpRequestMessage
                    {
                        RequestUri = new Uri("http://localhost/api/query/BarQuery?Id=1")
                    },
                    Configuration = configuration
                };
            }

            [Test]
            public async Task should_work()
            {
                var result = await (await Subject.HandleGet("BarQuery")).ExecuteAsync(CancellationToken.None);
                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 Subject.HandleGet("FailQuery");

                await result.ShouldBeErrorAsync("The query type 'FailQuery' could not be found");
            }

            QueryController Subject;
        }
    }
}