Web API Filters

Web API Filters

Introduction Web API filters are components in the ASP.NET Web API framework that allow you to implement cross-cutting concerns, such as logging, authentication, authorization, and exception handling, among others. Filters can be applied at different levels within the Web API pipeline, providing a flexible way to handle common functionality in a modular and reusable manner.

Types of Filters There are four main types of filters in Web API:

1. Authorization Filters: These filters are responsible for handling authentication and authorization logic before executing an action. They can be used to ensure that only authenticated and authorized users can access certain resources. An example of an authorization filter is the [Authorize] attribute.

csharp
[Authorize]
public IHttpActionResult Get(int id)
{
    // Retrieve and return resource with the specified ID
}

2. Action Filters: Action filters are used to perform additional processing before and after an action method is executed. They can be used to modify the input or output of an action, or to perform logging or auditing tasks. An example of an action filter is the [ActionFilter] attribute.

csharp
[ActionFilter]
public IHttpActionResult Post([FromBody] MyModel model)
{
    // Process and store the received data
}

3. Exception Filters: Exception filters are responsible for handling exceptions that occur during the execution of an action method. They can be used to log exceptions, transform them into a different format, or provide custom error messages to the client. An example of an exception filter is the [ExceptionFilter] attribute.

csharp
[ExceptionFilter]
public IHttpActionResult Get(int id)
{
    try
    {
        // Retrieve and return resource with the specified ID
    }
    catch (NotFoundException ex)
    {
        return NotFound();
    }
}

4. Result Filters: Result filters are used to modify the result of an action method before it is returned to the client. They can be used to apply transformations to the data, add headers to the response, or perform other post-processing tasks. An example of a result filter is the [ResultFilter] attribute.

csharp
[ResultFilter]
public IHttpActionResult Get(int id)
{
    // Retrieve and return resource with the specified ID
}

Filter Execution Order Filters are executed in a specific order within the Web API pipeline. The order of execution is as follows:

1. Authorization Filters
2. Action Filters (OnActionExecuting)
3. Exception Filters (OnException)
4. Action Filters (OnActionExecuted)
5. Result Filters (OnResultExecuting)
6. Action Execution
7. Result Filters (OnResultExecuted)

By understanding the filter execution order, you can control the flow of your application and apply the necessary logic at each step.

Conclusion Web API filters provide a powerful way to implement common functionality in a modular and reusable manner. By applying filters at various levels within the Web API pipeline, you can handle cross-cutting concerns efficiently and maintain clean and organized code. Understanding the different types of filters and their execution order is essential for building robust and secure Web API applications.