How deeply does Building Web APIs with ASP.NET Core cover result resource?

Explains the generic return-type change and manual validation branches, stopping short of framework internals.

Result resource

As explained in Building Web APIs with ASP.NET Core

ActionResult is an ASP.NET Core action return type that can represent either a typed response value or an HTTP action result.

ActionResult<T> lets an ASP.NET Core action return either a successful typed value or an HTTP action result. For example, an action returning Task<ActionResult<RestDTO<Domain[]>>> can produce domain data when validation succeeds, or an ObjectResult containing validation details when it fails. section 6.2.3

Use the return type when an action must:

Return a JSON object for a successful request. section 6.2.3
Return different HTTP statuses, such as 501 for an unsupported page size or 400 for an invalid sort order. section 6.2.3

Verify both response paths

Call /Domains?pageSize=101 and /Domains?sortOrder=InvalidValue. Open the browser Network tab and inspect each HTTP status, not only the response body. section 6.2.3

How Building Web APIs with ASP.NET Core covers it

Cover of Building Web APIs with ASP.NET Core

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Also explained in

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ASP.NET Core in Action, 3eActionResult<T> is an ASP.NET Core MVC result type that allows an action method to return either a typed value or an arbitrary HTTP action result.
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Pro ASP.NET Core 7, Tenth EditionAn action result is an object representing a response produced by an MVC action method.
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.NET in Action, Second EditionActionResult is an ASP.NET Core result abstraction that represents the outcome of handling a web request, including its response content and HTTP status code.

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Related concepts

IActionResultimplements · IActionResult is an ASP.NET Core MVC interface implemented by objects that represent the result of processing an HTTP request.
ControllerBaseproduced by · ControllerBase is the ASP.NET Core MVC base class providing controller behavior and action-result helpers without view-specific functionality.
web API action methodused by · A web API action method is a controller method associated with a matched HTTP request that processes it and produces a response.
resourcekind of · An API resource is a conceptual entity or target exposed through an interface and addressable for access or manipulation.
ViewResultincludes · ViewResult is an MVC action-result type that represents rendering a view with an optional name and model.

This explainer was generated by Manning's knowledge graph from the text of Building Web APIs with ASP.NET Core. The section links point to the parts of the book it draws on.