Mastering ASP.NET Web API

Writing custom route constraints

Till now, we used the inbuilt route constraints; they serve a large number of use cases, but different business requirements could lead to the need to write custom constraints. Writing custom Route constraints is achieved using the IRouteConstraint interface present in the Microsoft.AspNetCore.Routing namespace.

The interface has a Match method, which takes in HttpContext, IRoute, routeKey, values, and RouteDirection. When the Match method is implemented, if the condition for the constraint matches with the parameter value, it returns TRUE, else FALSE.

For example, let's take a business use case for custom route constraints which specifies that the parameter should contain the domain name as @packt.com, else ...