ASP.NET Core offers a variety of built-in route constraints, sometimes your application requires more specialized validation rules. Custom route constraint classes allow you to define your own criteria for determining whether a parameter value is valid. Key Requirements Implement IRouteConstraint: Create a class that implements the IRouteConstraint interface. Match Method: Implement the Match method, which will contain your custom validation logic. This method receives several parameters: httpContext: The current HttpContext. route: The IRouter object associated with the route. routeKey: The name of the route parameter being validated. values: A dictionary containing the route values. routeDirection: Indicates whether the route is being matched for an incoming request or for generating a URL. Return true or false: The Match method must return true if the parameter value is valid according to your constraint, and false otherwise.
Code // MonthsCustomConstraint.cs public class MonthsCustomConstraint : IRouteConstraint { public bool Match(HttpContext? httpContext, IRouter? route, string routeKey, RouteValueDictionary values, RouteDirection routeDirection) { // Check if the parameter value exists if (!values.ContainsKey(routeKey)) { return false; // Not a match }
Regex regex = new Regex(“^(apr|jul|oct|jan)$”); string? monthValue = Convert.ToString(values[routeKey]);
if (regex.IsMatch(monthValue)) { return true; // It’s a match } return false; // Not a match } }
Using the Custom Constraint // … (in your endpoint configuration) … endpoints.Map(“sales-report/{year:int:min(1900)}/{month:months}”, async context => { // … your endpoint handler logic … });
Notice the :months constraint after the month parameter. This indicates that the value for month should be validated against the MonthsCustomConstraint class.
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Route Constraints in Asp.net Core