Unable to cast Object of type(...) to ICommandHandler

[pkskelly]

Following your recent Part 1 video on using FunctionMonkey and once I have a simple structure created to verify the plumbing works, I get the following error:

[3/17/19 2:00:58 AM] AzureFromTheTrenches.Commanding: Error occurred during command execution. Anonymously Hosted DynamicMethods Assembly: Unable to cast object of type 'ThreeWill.Functions.Application.Handlers.HelloWorldCommandHandler' to type 'AzureFromTheTrenches.Commanding.Abstractions.ICommandHandler`2[ThreeWill.Functions.Commands.HelloWorldCommand,System.String]'.``` 

Using the v1.0.0 versions of FunctionMonkey an FunctionMonkey.Compiler.  
Using v9.0.1 of the Commanding Abstractions.  
Azure Functions Core Tools 2.4.401
Function Runtime Version: 2.0.12309.0

Have you seen this before?  Both macOS w/ VS Code and VS 2017 enterprise get the same result.  Debugging does not seem to get past some of the Function framework prices, or maybe I am missing a way to debug into the actual issue.  

I'll keep digging, but thought I would ask if this might be something simple.  

[JamesRandall]

Can you share your HelloWorldCommandHandler and HelloWorldCommand implementations?

[pkskelly]

Hello James, thanks for the quick response! Below are the sample files.

The following is in a netstandard2.0 library named "ThreeWill.Functions.Commands"

using System;
using AzureFromTheTrenches.Commanding.Abstractions;

namespace ThreeWill.Functions.Commands
{
    public class HelloWorldCommand : ICommand<string>
    {
        public string Name { get; set; }
    }

}

The following is in a netstandard2.0 library named "ThreeWill.Functions.Application"

using System;
using System.Text;
using System.Collections.Generic;
using System.Threading.Tasks;
using AzureFromTheTrenches.Commanding.Abstractions;
using ThreeWill.Functions.Commands;

namespace ThreeWill.Functions.Application.Handlers
{
    internal class HelloWorldCommandHandler : ICommandHandler<HelloWorldCommand>
    {
        public Task ExecuteAsync(HelloWorldCommand command)
        {
            throw new NotImplementedException();
        }
    }
}

I can also share the entire solution if you'd like. Nothing in there of any import yet. Let me know. Very interested to get FunctionMonkey working - Thanks for creating it!

[pkskelly]

@JamesRandall, I created a private repo and added you as a collaborator to the project. Likely something simple on my part is missing. :-)

[JamesRandall]

Thanks for that. The line:

internal class HelloWorldCommandHandler : ICommandHandler<HelloWorldCommand>

needs to read

internal class HelloWorldCommandHandler : ICommandHandler<HelloWorldCommand, string>

Your ExecuteAsync method signature will then become:

public async Task<string> ExecuteAsync(HelloWorldCommand command, string previousResult)

If your command returns a result the command handler needs that as part of its generic type definition.

Hope that helps! Will leave this issue open for the moment in case not!

[pkskelly]

Thanks James, I knew it was likely something simple! Sorry for the bother but very much appreciate the response and patience! Works perfectly!

[JamesRandall]

No problem at all.

I moved Function Monkey to v1.0.0 since I recorded the first 2 videos and there were a couple of breaking changes - in case you run into any issues there is a very short doc here that describes them and how to resolve them:

https://functionmonkey.azurefromthetrenches.com/guides/upgradingTo1.0.html

I also cover them in part 3 which I should be publishing later today.