ASP.NET Tutorial : Exploring Filters within.NET Core

When it comes to web development,.NET Core is a strong and adaptable framework that provides a strong foundation for developing contemporary, scalable, and high-performing apps. The notion of filters is one of the key components that enhances.NET Core's extensibility and flexibility. With the use of filters, developers can add logic to the pipeline used to process requests or answers, allowing for the modular and reusable implementation of cross-cutting issues like authentication, logging, and exception handling.

What do.NET Core Filters do?

In.NET Core, filters are parts that let programmers run code either ahead of or behind particular request processing pipeline steps. They offer fine-grained control over the when and where the filter logic is implemented, and they can be applied globally to all actions, at the controller level, or at the action level. 

Categories of Filters
Authorization Filters: These are the programs that decide if a request is allowed to access a specific resource or not. They are frequently employed in the implementation of permission and authentication logic. Developers can restrict access to particular actions or controllers according to user roles, permissions, or other parameters by implementing authorization filters.

[Authorize]
public IActionResult SecureAction()
{
    // Code for the secure action
}

Action Filters: Action filters allow developers to execute code before and after the execution of an action method. This type of filter is beneficial for tasks such as logging, validation, or modifying the result of an action.

public class CustomActionFilter : IActionFilter
{
    public void OnActionExecuting(ActionExecutingContext context)
    {
        // Code executed before the action method
    }

    public void OnActionExecuted(ActionExecutedContext context)
    {
        // Code executed after the action method
    }
}

Result Filters: Result filters enable developers to execute code before and after the execution of the result that is returned by the action method. This can be useful for tasks such as modifying the response or logging the result.

public class CustomResultFilter : IResultFilter
{
    public void OnResultExecuting(ResultExecutingContext context)
    {
        // Code executed before the result is executed
    }

    public void OnResultExecuted(ResultExecutedContext context)
    {
        // Code executed after the result is executed
    }
}

Exception Filters: Exception filters allow developers to handle exceptions that occur during the processing of a request. This type of filter can be used to log exceptions, perform custom error handling, or redirect users to error pages.

public class CustomExceptionFilter : IExceptionFilter
{
    public void OnException(ExceptionContext context)
    {
        // Code to handle exceptions
    }
}

Applying Filters in .NET

Filters can be registered in the Startup.cs file or applied using attributes. One simple technique to add filter logic straight to the controllers or actions is to apply filters using attributes.

[TypeFilter(typeof(CustomActionFilter))]
public class SampleController : Controller
{
    // Controller actions
}

As an alternative, the Startup.cs file allows filters to be registered globally.

services.AddControllers(options =>
{
    options.Filters.Add<CustomActionFilter>();
});

A strong method for adding modular and reusable logic to the request processing pipeline is offered by filters in.NET Core. Developers can encapsulate cross-cutting concerns in a tidy and structured way by using filters to handle tasks like authentication, logging, and altering the outcome of an operation. Developers can improve the scalability, maintainability, and general quality of their.NET Core web apps by utilizing filters.

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