Migrating old websites & Rewrite maps in IIS 7

If you’re migrating to a new website and need to map old IDs to new IDs, I’ve just discovered that the UrlRewrite plugin in IIS has a great feature I hadn’t come across before called rewriteMaps. This means instead of writing a whole bunch of indentical looking rewrite rules, you can write one – and then simply list the ID mappings.

The syntax of the RegEx takes a bit of getting used to, but in our case we needed to map

/(various|folder|names|here)/display.asp?id=[ID]

to a new website url that looked like this:

/show/[NewId]

You can define a rewriteMap very simply – most examples I saw included full URLs here, but we just used the ID maps directly:

<rewriteMaps>
  <rewriteMap name="Articles">
    <add key="389" value="84288" />
    <add key="525" value="114571" />
    <add key="526" value="114572" />
  </rewriteMap>
</rewriteMaps>

You can reference a rewriteMap using {MapName:{SomeCapturedValue}}, so if SomeCapturedValue equalled 525 then you’d get back 114571 in the list above.

Because we’re looking to match a querystring based id, and you can’t match queryString parameters in the primary match clause, we needed to add a condition, and then match on that captured condition value instead, using an expression like this:

http://www.newdomain.com/show/{Articles:{C:1}}/

The final rule XML follows:

<rule name="Redirect rule for Articles" stopProcessing="true">
  <match url="(articles|java|dotnet|xml|databases|training|news)/display\.asp" />
  <conditions>
    <add input="{QUERY_STRING}" pattern="id=([0-9]+)" />
  </conditions>
  <action type="Redirect" url="http://www.developerfusion.com/show/{Articles:{C:1}}/" appendQueryString="false" />
</rule>