Filters in asp net core web api

Introduction

ASP.NET is a popular programming language used for building web applications. One of the key features of ASP.NET is its ability to handle filters in web APIs. Filters are used to perform certain actions before or the execution of a web API method. In this article, we will explore how to use filters in ASP.NET Core Web API with examples.

What are Filters?

Filters in ASP.NET Core Web API are used to add additional to the execution pipeline of a web API method. They can be used to perform tasks such as authentication, authorization, logging, exception handling, and more. Filters can be applied globally to all API methods or can be applied to specific methods or controllers.

Types of Filters

There are four types of filters in ASP.NET Core Web API:

  1. Authorization Filters: filters are used to perform authentication and authorization tasks before executing a web API method. They can be used to restrict access to certain API methods on user roles or permissions.
  2. Action Filters: Action filters are used to perform actions before or after the execution of a web API method. They can be used to log and responses, modify the input or output of a method, or perform any other custom action.
  3. Exception Filters: Exception filters are used to handle exceptions that occur during the execution of a web API method. They can be used to log exceptions, return custom error messages, or perform any other action when an exception occurs.
  4. Result Filters: Result filters are used to modify the result of a web API method before it is returned to the client. They can be used to add additional data to the result, modify the status code, or perform any other action on the result.

Using Filters in ASP.NET Core Web API

To use filters in ASP.NET Core Web API, you need to define the filters and them to the desired methods or controllers. Let's take a look at some examples:

Example 1: an Authorization Filter

To apply an authorization filter to a web API method, you can use the [Authorize] attribute. This attribute restricts access to the method to only authenticated users. Here's an example:


[Authorize]
[HttpGet]
public  Get()
{
    // Method logic here
}

Example 2: Applying an Action Filter

To apply an action filter to a web API method, you can a custom action filter class by implementing the IActionFilter interface. Here's an example:


public class LogActionFilter : IActionFilter
{
    public void OnActionExecuting(ActionExecutingContext context)
    {
        // Logic to be executed before the method
    }

    public void OnActionExecuted(ActionExecutedContext context)
    {
        // Logic to be executed after the method
    }
}

[ServiceFilter(typeof(LogActionFilter))]
[HttpGet]
public IActionResult Get()
{
    // Method logic here
}

Example 3: Applying an Exception Filter

To apply an exception filter to a web API method, you can create a custom exception filter class by implementing the IExceptionFilter interface. Here's an example:


public class LogExceptionFilter : IExceptionFilter
{
    public void OnException(ExceptionContext context)
    {
        // Logic to handle the exception
    }
}

[ServiceFilter(typeof(LogExceptionFilter))]
[HttpGet]
public IActionResult Get()
{
    // Method logic here
}

Example 4: Applying a Result Filter

To apply a result filter to a web API method, you can create a custom result filter class by implementing the IResultFilter interface. Here's an example:


public class ModifyResultFilter : IResultFilter
{
    public void OnResultExecuting(ResultExecutingContext context)
    {
        // Logic to modify the result before it is returned
    }

    public void OnResultExecuted(ResultExecutedContext context)
    {
        // Logic to be executed after the result is returned
    }
}

[ServiceFilter(typeof(ModifyResultFilter))]
[HttpGet]
public IActionResult Get()
{
    // Method logic here
}

Conclusion

Filters in ASP.NET Core Web API are a powerful feature that allows you to add additional logic to the execution pipeline of your web API methods. By using types of filters, you can perform tasks such as authentication, authorization, logging, exception handling, and result modification. By applying filters to specific methods or controllers, you can customize the behavior of your web API and enhance its functionality.

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