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Route.Constraints Property

Gets or sets a dictionary of expressions that specify valid values for a URL parameter.

Namespace:  System.Web.Routing
Assembly:  System.Web (in System.Web.dll)

public RouteValueDictionary Constraints { get; set; }

Property Value

Type: System.Web.Routing.RouteValueDictionary
An object that contains the parameter names and expressions.

The Constraints property enables you to limit acceptable values for a URL parameter that is processed by a route. You assign a RouteValueDictionary object to the Constraints property. Each element in the RouteValueDictionary object contains the name of a parameter and one of the following:

  • A string that defines a regular expression. The regular expression is case-insensitive.

  • An object that implements the IRouteConstraint interface and that includes a Match method.

The HttpMethodConstraint class implements the IRouteConstraint interface. You can include an instance of the HttpMethodConstraint class as a constraint to specify which HTTP verbs are acceptable for the route.

The following example shows how to create a Route object and set the Constraints, DataTokens, and Defaults properties.

void Application_Start(object sender, EventArgs e) 
{
    RegisterRoutes(RouteTable.Routes);
}

public static void RegisterRoutes(RouteCollection routes)
{
    Route reportRoute = new Route("{locale}/{year}", new ReportRouteHandler());
    reportRoute.Defaults = new RouteValueDictionary { { "locale", "en-US" }, { "year", DateTime.Now.Year.ToString() } };
    reportRoute.Constraints = new RouteValueDictionary { { "locale", "[a-z]{2}-[a-z]{2}" }, { "year", @"\d{4}" } };
    reportRoute.DataTokens = new RouteValueDictionary { { "format", "short" } };
    routes.Add(reportRoute);
}

The following example shows a Route object whose Constraints property contains a parameter named httpMethod with an instance of the HttpMethodConstraint class for the value.

void Application_Start(object sender, EventArgs e) 
{
    RegisterRoutes(RouteTable.Routes);
}

public static void RegisterRoutes(RouteCollection routes)
{
    string[] allowedMethods = { "GET", "POST" };
    HttpMethodConstraint methodConstraints = new HttpMethodConstraint(allowedMethods);

    Route reportRoute = new Route("{locale}/{year}", new ReportRouteHandler());
    reportRoute.Constraints = new RouteValueDictionary { { "httpMethod", methodConstraints } };

    routes.Add(reportRoute);
}

.NET Framework

Supported in: 4.5, 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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