Using Function Monkey with MediatR

If you're looking for help with C#, .NET, Azure, Architecture, or would simply value an independent opinion then please get in touch here or over on Twitter.

There are a lot of improvements coming in v4 of Function Monkey and the beta is currently available on NuGet. As the full release approaches I thought it would make sense to introduce some of these new capabilities here.

In order to simplyify Azure Functions development Function Monkey makes heavy use of commanding via a mediator and ships with my own mediation library. However there’s a lot of existing code out their that makes use of the popular MediatR library which, if Function Monkey supported, could fairly easily be moved into a serverless execution environment.

Happily Function Monkey now supports just this! You can use my existing bundled mediator, bring your own mediator, or add the shiny new FunctionMonkey.MediatR NuGet package. Here we’re going to take a look at using the latter.

First begin by creating a new, empty, Azure Functions project and add three NuGet packages:


At the time of writing be sure to use the prerelease packages version 4.0.39-beta.4 or later.

Next create a folder called Models. Add a class called ToDoItem:

public class ToDoItem
    public Guid Id { get; set; }
    public string Title { get; set; }
    public bool IsComplete { get; set; }

Now add a folder called Services and add an interface called IRepository:

internal interface IRepository
    Task<ToDoItem> Create(string title);

And a memory based implementation of this called Repository:

internal class Repository : IRepository
    private readonly List<ToDoItem> _items = new List<ToDoItem>();
    public Task<ToDoItem> Create(string title)
        ToDoItem newItem = new ToDoItem()
            Title = title,
            Id = Guid.NewGuid(),
            IsComplete = false
        return Task.FromResult(newItem);

Now create a folder called Commands and in here create a class called CreateToDoItemCommand:

public class CreateToDoItemCommand : IRequest<ToDoItem>
    public string Title { get; set; }

If you’re familiar with Function Monkey you’ll notice the difference here – we’d normally implement the ICommand<> interface but here we’re implementing MediatR’s IRequest<> interface instead.

Next create a folder called Handlers and in here create a class called CreateToDoItemCommandHandler as shown below:

internal class CreateToDoItemCommandHandler : IRequestHandler<CreateToDoItemCommand, ToDoItem>
    private readonly IRepository _repository;

    public CreateToDoItemCommandHandler(IRepository repository)
        _repository = repository;
    public Task<ToDoItem> Handle(CreateToDoItemCommand request, CancellationToken cancellationToken)
        return _repository.Create(request.Title);

Again the only real difference here is that rather than implement the ICommandHandler interface we implement the IRequestHandler interface from MediatR.

Finally we need to add our FunctionAppConfiguration class to the root of the project to wire everything up:

public class FunctionAppConfiguration : IFunctionAppConfiguration
    public void Build(IFunctionHostBuilder builder)
            .Setup(sc => sc
                .AddSingleton<IRepository, Repository>()
            .Functions(functions => functions
                .HttpRoute("todo", route => route

Again this should look familiar however their are two key differences. Firstly in the Setup block we use MediatR’s IServiceCollection extension method AddMediatR – this will wire up the request handlers in the dependency injector. Secondly the .UseMediatR() option instructs Function Monkey to use MediatR for its command mediation.

And really that’s all their is to it! You can use both requests and notifications and you can find a more fleshed out example of this on GitHub.

As always feedback is welcome on Twitter or over on the GitHub issues page for Function Monkey.


  • If you're looking for help with C#, .NET, Azure, Architecture, or would simply value an independent opinion then please get in touch here or over on Twitter.

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