Attributes in Action Filters

Action filters in ASP.NET Core allow you to execute custom logic before or after an action method runs. The most common way to apply them is through attributes.

1. TypeFilterAttribute

TypeFilterAttribute is useful when you need to create a filter dynamically and pass constructor arguments manually.

public class CustomAuthorizeAttribute : TypeFilterAttribute
{
    public CustomAuthorizeAttribute(string role) : base(typeof(CustomAuthorizationFilter))
    {
        Arguments = new object[] { role };
    }
}

🔹 Why use it?

• Allows passing non-service arguments to filters.
• Uses dependency injection for constructor dependencies.

2. ServiceFilterAttribute

Use ServiceFilterAttribute when the filter is already registered as a service in the DI container.

[ServiceFilter(typeof(CustomAuthorizationFilter))]

🔹 Why use it?

• Reuses existing services, reducing object instantiation.
• Ensures filter dependencies are managed by DI.

3. Custom Authorization Example

Here's a practical example using TypeFilterAttribute:

public class CustomAuthorizationFilter : IAuthorizationFilter
{
    private readonly string _role;
    public CustomAuthorizationFilter(string role) => _role = role;

    public void OnAuthorization(AuthorizationFilterContext context)
    {
        var user = context.HttpContext.User;
        if (!user.IsInRole(_role))
        {
            context.Result = new ForbidResult();
        }
    }
}

Applying the Filter

[CustomAuthorize("Admin")]
public IActionResult SecureEndpoint()
{
    return Ok("You have access!");
}

🚀 Best Practice: Use TypeFilterAttribute if you need custom arguments, otherwise use ServiceFilterAttribute to leverage DI.

Peace... 🍀