During my PDC talk I had shown some of the snippets that can come handy while using Web.Config Transformations� This post is intended to share the XDT snippets and instructions on how to install them to use them with VS 2010�
- Download XDT zip file from my SkyDrive
- Unzip the files and copy the inner XDT folder into %Program Files%\Microsoft Visual Studio 10.0\Xml\1033\Snippets
- After this the XDT snippets will be available for you to use within any XML file within VS 2010�
To know how to use XDTs for Web.Config file please check out the post about Web.Config Transformations
Few interesting points about Transforms & Locators which are worth noting to do pretty powerful stuff with your XML are:
- Transforms - Transforms act on a XML node i.e. from XDT engine standpoint the node on which a transform is found is plucked out of the document and passed as a node to the Transform itself (e.g. �SetAttributes� Transform)� The Transform class internally implements the logic of modifying the node with its own special logic (i.e. setting attributes in case of �SetAttributes� Transform) and returns back the node to the engine� The XDT engine then replaces the new node into the document� The engine also passes the handle of the parent node to the transform which the transform can then play around with (e.g. �Insert� Transform receives a new node as well as the parent node and has the DOM code of inserting the new node under the parent�)
- Locators � XDT usually traverses through the XML document and constructs the XPath all along e.g. when it hits the add node under connectionStrings in web.config it has already constructed the XPath (/configuration/connectionString/add)� Locators help with narrowing down the XPath so that the correct node can be picked up� Check out the example below:
<connectionStrings>
<add name="1stDB"
connectionString="Data Source=Server1;Initial Catalog=DB1;Integrated Security=True"
xdt:Transform="SetAttributes" />
<add name="2ndDB"
connectionString="Data Source=Server2;Initial Catalog=DB2;Integrated Security=True"
xdt:Transform="SetAttributes" xdt:Locator="Match(name)"/>
</connectionStrings>
Based on the standard logic of XPath traversing XDT will always pick up the first �add� node i.e. one with 1stDB in the example below� That may not be always desirable� In XDT we could have implemented the logic to do special things for appSettings & connectionStrings but then that would have made XDT specific to web.config instead we implemented Locators which now allows XDT to be general purposes XML transformation engine� In the above example if we use a Locator called xdt:Locator=�Match(name)� on the 2ndDB then as soon as the XDT engine encouters a locator it calls the class implementing it (i.e. �Match� and allows it to play with the XPath that is being generated� In this case the match locator will help construct the XPath as /configuration/connectionString/add[@name=�2ndDB�]
The high level takeaway here is that when you play around with the snippets for XDT keep the above concepts for Transforms & Locators in mind and with the quick snippet explanations of each transforms and locators you should be able to very easily use all of them� If you encounter any issues plz feel free to reach out�
Thanks!!
-Vishal
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