How can I define a custom attribute in ASP.NET Core Web API for endpoints and return an ObjectResult in it?

Question

I am creating an ASP.NET Core Web API project. I want to define an attribute (for example ExampleAttribute) and access the HttpContext in it and doing some action and finally return an ObjectResult if necessary, or continue.

I don't know if I am doing it right or not, but I want to define an attribute in this way:

    public class DeveloperTaskAttribute : Attribute
    {
        // using HttpContext and doing some action

        // I will returning BadRequest("") if necessary
        // or continue...
    }

And I'm trying to use this attribute on this endpoint:

    [HttpGet]
    [ExampleAttribute] // using attribute
    public IActionResult EndPoint1() 
    {      
        // doing some action in endpoint1
    }

How can I do this?

Thanks for any help.

Roozbeh · Accepted Answer · 2023-07-30 06:35:19Z

Instead of using attribute, use ActionFilter and Attribute.

https://learn.microsoft.com/en-us/aspnet/mvc/overview/older-versions-1/controllers-and-routing/understanding-action-filters-cs

Get custom attributes via ActionExecutingContext from controller .Net Core

First define an attribute :

[AttributeUsage(AttributeTargets.Method)]
public sealed class SampleAttribute : Attribute
{ 
}

Then define a class which is implement IActionFilter :

public sealed class SampleActionFilter : IActionFilter
{
    public void OnActionExecuted(ActionExecutedContext context){ }
    public void OnActionExecuting(ActionExecutingContext context)
    {
        var attrib = (context.ActionDescriptor as ControllerActionDescriptor).MethodInfo.GetCustomAttributes<SampleAttribute>().FirstOrDefault();
        if (attrib is null) return;

        if (!someCondition) return;

        context.HttpContext.Response.StatusCode = 400;
        context.Result = new ObjectResult(new { done = false });
    }
}

To register this action filter :

services.AddControllers(mvcOptions => { mvcOptions.Filters.Add<SampleActionFilter>(); });

bkh6722 · Accepted Answer · 2024-09-08 15:46:54Z

You need to use ActionFilterAttribute Only:

Defining a new Attribute:


    public class TestAttribute : TypeFilterAttribute
        {
            public TestAttribute() : base(typeof(TestFilter))
            {
            }
    
            private class TestFilter : ActionFilterAttribute
            {
                private readonly MyDbContext _myDbContext;
    
                public TestFilter(MyDbContext myDbContext)
                {
                    _myDbContext = myDbContext;
                }
    
                public override void OnActionExecuting(ActionExecutingContext context)
                {
                    // Dont use async - await methods !
                    // Do something
                    var user= context.HttpContext.User    
                }
            }
    
    
        }

Note: You must use the word Attribute at the end of the name

And using in controller:

        [Test]
        [HttpGet]
        [Route("Example")]
        public async Task<IActionResult> ExampleMethod()
        {}

Documentation: https://www.andybutland.dev/2020/06/dependency-injection-in-aspnet-core-attributes.html

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