Validation Filter in Azure Function

Question

Problem

I am using fluent validation for model validation and I want it to be done by ValidationFilter in azure function. I already did it in asp.net core app but I don't know how to do it in azure functions

Code

MyValidator

using FluentValidation;

namespace MyLocker.Models.Validations
{
    public class PortfolioFolderVMValidator : AbstractValidator<PortfolioFolderVM>
    {
        public PortfolioFolderVMValidator()
        {
            RuleFor(reg => reg.Title).NotEmpty().WithName("Title").WithMessage("{PropertyName} is required");
            RuleFor(reg => reg.UserId).NotEmpty().WithName("UserId").WithMessage("{PropertyName} is required");
        }
    }
}

Validate Model Action Filter

using System.Collections.Generic;
using System.Linq;
using System.Net;
using Microsoft.AspNetCore.Mvc.Filters;
using MyLocker.Models.Common;

namespace MyLocker.WebAPI.Attributes
{
    public sealed class ValidateModelAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext context)
        {
            if (!context.ModelState.IsValid)
            {
                var errors = context.ModelState.Keys.SelectMany(key => context.ModelState[key].Errors.Select(error => new ValidationError(key, error.ErrorMessage))).ToList();
                context.Result = new ContentActionResult<IList<ValidationError>>(HttpStatusCode.BadRequest, errors, "BAD REQUEST", null);
            }
        }
    }
} 

Startup

after that add it in startup.cs class like this

 services.AddMvc(opt => opt.Filters.Add(typeof(ValidateModelAttribute)))
            .AddFluentValidation(fv => fv.RegisterValidatorsFromAssemblyContaining<PortfolioFileModelValidator>())

I tried it in azure function but there are different classes and interface in it.

Answer 1

At present , there are 2 types of filter are available with Azure function:

• FunctionInvocationFilterAttribute

  As the name indicates, Filter used to execute PRE and POST processing logic when target job function is invoked.

• FunctionExceptionFilterAttribute

  Exception Filter will be called whenever there is an exception thrown by the Azure Function.

But you can write a wrapper on top of Azure function which will help you write the clean code.

For the wrapper based implementation , you can refer below code repo:

https://gist.github.com/bruceharrison1984/e5a6aa726ce726b15958f29267bd9385#file-fluentvalidation-validator-cs

Also alternatively you can implement the pipeline for validation the data model passed to azure function. You can find the complete reference in below repo:

https://github.com/kevbite/AzureFunctions.GreenPipes/tree/master/src/AzureFunctions.GreenPipes

Out of these 2 approach, Wrappers is more cleaner and easier to implement.

Let me know if you need any other help.