What is the role of a controller in ASP.NET Core Web API or MVC?

In ASP.NET Core Web API or MVC, a controller plays a crucial role in handling incoming HTTP requests and generating appropriate HTTP responses. Here's an overview of the role of a controller in both scenarios:

1. ASP.NET Core Web API:

   • In Web API, controllers are responsible for defining endpoints (HTTP methods such as GET, POST, PUT, DELETE) and processing incoming HTTP requests.
   • Each controller class typically represents a logical grouping of related endpoints.
   • Actions within the controller are annotated with attributes such as [HttpGet], [HttpPost], [HttpPut], [HttpDelete], etc., to define the HTTP verb they respond to.
   • Controllers often interact with services or repositories to retrieve or manipulate data before returning a response.

2. ASP.NET Core MVC:

   • In MVC (Model-View-Controller) pattern, controllers handle user input, manipulate the model (data), and select the appropriate view to render to the user.
   • Controllers receive user requests, process them, and determine which view to render based on the requested action.
   • Actions within the controller correspond to user actions (e.g., clicking a button, submitting a form) and are responsible for coordinating the flow of data between the model and the view.
   • Controllers interact with models (data access layer) to perform CRUD operations or any other necessary business logic.
   • Controllers often return views (HTML templates) to be rendered in the user's browser, along with any necessary data to populate those views.

In both scenarios, controllers play a pivotal role in the application's architecture, providing the logic to handle incoming requests, process data, and generate appropriate responses. They help to maintain separation of concerns by keeping the handling of HTTP requests separate from business logic and presentation concerns.