T4 (Text Template Transformation Toolkit) Code Generation - Best Kept Visual Studio Secret

Rob beat me to it. Blogging about T4 (the Text Template Transformation Toolkit)had been on my list literally for a year. He and I were singing itspraises last night. Hopefully I can add something small to theconversation.

What's the story? Well, T4 is a code generator built right into Visual Studio. To be clear, you HAVE THIS NOW on your system…go play. Now's the time to introduce code generation to your company. If you're doing something twice or more, manually, in your company, generate it.

However,it's not deep-deep built in, because there's no item templates in File |New Item and there's no intellisense or syntax highlighting.

You don't need this, but if you want really get the most out of T4, first, head over to Clarius Consulting and get their "T4 Editor Community Edition." That'll get you some basic coloring. They have a pay version that gets you more if you want.

Now, go into Visual Studio and make a Console App (or any app) and add a Text File, but name it something with a .tt extension.You'll get a warning since it's a generator, that someone couldgenerate evil. Click OK if you are cool with potential evil. ;)

Now,look in Solution Explorer at the .tt file. If you're using C#, you'llhave a sub .cs file, or if you're using VB, a sub .vb file. That's thefile that will hold the result of the generation. This is the samevisual metaphor used to the express the template/generated filerelationship with .designer files you've seen elsewhere in VisualStudio.

If you look in the Properties for the .tt file, you'llsee it's using a CustomTool listed as the "TextTemplatingFileGenerator."This custom tool extensibility point is how things like XSD and WSDLcode generators hook in to generate their artifacts.

T4 can generate any kind of text file, not just code. Whatever you like. You can use it in your projects, as above, or you can call T4 from the command-line.

Aside from Kzu and the folks at Clarius, Rob notes that Oleg Sych has a great collection of T4 resources. He's got some great Tutorials:

• Creating your first code generator
• Troubleshooting code generation errors
• Debugging code generation files
• Creating reusable code generation templates
• Creating complex code generators
• Reusing code generators on multiple projects

Here's some of the links from Oleg's blog.

• How to create a simple T4 template
• How to use T4 to generate .config files
• How to use T4 to generate Decorator classes
• How to use T4 to generate CRUD stored procedures
• How to use T4 to generate strongly-typed navigation class in ASP.NET (by Kirill Chilingarashvili)
• How to use T4 to generate strongly-typed AzMan wrapper
• How to generate multiple outputs from single T4 template
• T4 template for generating ADO.NET Entity Framework Stored Procedures  (by David DeWinter)
• T4 script for generating ADO.NET Entity Framework Views (by ADO.NET team)
• T4 template for generating LINQ to SQL Data Context (by Damien Guard)
• T4 template for generating WiX source files (by New Age Solutions)
• T4 template for generating SQL view from C# enumeration
• MSBuild task for transforming T4 templates (by Elton Stoneman)
• T4 template for generating state machines in C# (by Andrew Matthews)

Oleg also has a CodePlex project called T4 Toolbox that is a library of T4 templates that get added to File | New Item.

Also, check out Damien Guard's T4 templates that are a wholesale replacement of code that LINQ to SQL generates. Here's an example, where I use Damien's T4 templates against the sample Chinook Database.

Noticethat I've named the .tt file the same as the .dbml, so Damian's codecan find it. I also continue to let original LINQ to SQL generate it's.designer.cs file, but make that file's Build Action "None" so it's notever compiled. That effectively puts Damian's code in charge.

Here'sa screenshot showing a bit of Damian's T4 template using the syntaxhighlighting from the Clairus T4 Visual Studio free download. If I'd paythem, I'd get intellisense and syntax highlighting inside thecode blocks also. It looks like a lot like ASP.NET Web Forms, orVelocity, or any templating language really. The code blocks are whereyour logic is and outside the codeblocks is the template for whateveryou want to generate. Notice how Damien gets input and sets output. Youhave full control, you can read files off the file system, from withyour project, etc. He sets the output extension also. I like to use.g.cs or .g.vb, myself. In this example his generated file isChinook.generated.cs.

I particularly like Damien's examplebecause he's swapping out parts of LINQ to SQL that he didn't like (thegenerated code) while keeping the part he did (the general mode, thedesigner, the dbml file.) If you don't like something, fix it.

Plus, it all works in Visual Studio without installing anything.

If you're doing Code Gen, or thinking about it, check out T4 as it's a great place to start. Also, search my blog for "Code Generation" as I was livign and breathing it with CodeSmith for the many years I worked at Corillian. Have fun!