76 lines
3.1 KiB
Markdown
76 lines
3.1 KiB
Markdown
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---
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title: "Creating a Route Constraint (VB) | Microsoft Docs"
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author: StephenWalther
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description: "In this tutorial, Stephen Walther demonstrates how you can control how browser requests match routes by creating route constraints with regular expressions."
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ms.author: aspnetcontent
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manager: wpickett
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ms.date: 02/16/2009
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ms.topic: article
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ms.assetid: b7cce113-c82c-45bf-b97b-357e5d9f7f56
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ms.technology: dotnet-mvc
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ms.prod: .net-framework
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msc.legacyurl: /mvc/overview/older-versions-1/controllers-and-routing/creating-a-route-constraint-vb
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msc.type: authoredcontent
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---
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Creating a Route Constraint (VB)
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====================
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by [Stephen Walther](https://github.com/StephenWalther)
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> In this tutorial, Stephen Walther demonstrates how you can control how browser requests match routes by creating route constraints with regular expressions.
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You use route constraints to restrict the browser requests that match a particular route. You can use a regular expression to specify a route constraint.
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For example, imagine that you have defined the route in Listing 1 in your Global.asax file.
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**Listing 1 - Global.asax.vb**
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[!code-vb[Main](creating-a-route-constraint-vb/samples/sample1.vb)]
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Listing 1 contains a route named Product. You can use the Product route to map browser requests to the ProductController contained in Listing 2.
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**Listing 2 - Controllers\ProductController.vb**
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[!code-vb[Main](creating-a-route-constraint-vb/samples/sample2.vb)]
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Notice that the Details() action exposed by the Product controller accepts a single parameter named productId. This parameter is an integer parameter.
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The route defined in Listing 1 will match any of the following URLs:
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- /Product/23
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- /Product/7
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Unfortunately, the route will also match the following URLs:
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- /Product/blah
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- /Product/apple
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Because the Details() action expects an integer parameter, making a request that contains something other than an integer value will cause an error. For example, if you type the URL /Product/apple into your browser then you will get the error page in Figure 1.
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[](creating-a-route-constraint-vb/_static/image1.png)
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**Figure 01**: Seeing a page explode ([Click to view full-size image](creating-a-route-constraint-vb/_static/image2.png))
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What you really want to do is only match URLs that contain a proper integer productId. You can use a constraint when defining a route to restrict the URLs that match the route. The modified Product route in Listing 3 contains a regular expression constraint that only matches integers.
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**Listing 3 - Global.asax.vb**
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[!code-vb[Main](creating-a-route-constraint-vb/samples/sample3.vb)]
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The regular expression \d+ matches one or more integers. This constraint causes the Product route to match the following URLs:
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- /Product/3
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- /Product/8999
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But not the following URLs:
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- /Product/apple
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- /Product
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These browser requests will be handled by another route or, if there are no matching routes, a *The resource could not be found* error will be returned.
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>[!div class="step-by-step"]
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[Previous](creating-custom-routes-vb.md)
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[Next](creating-a-custom-route-constraint-vb.md)
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