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Walkthrough: Debugging a Text Template that Accesses a Model

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When you modify or add text templates in a domain-specific language solution, you may get errors when the engine transforms the template to source code or when it compiles the generated code. The following walkthrough demonstrates some of the things you can do to debug a text template.

Note

For more information about text templates in general, see Code Generation and T4 Text Templates. For more information about debugging text templates, see Walkthrough: Debugging a Text Template.

Creating a Domain-Specific Language Solution

In this procedure, you create a domain-specific language solution that has the following characteristics:

Creating a text template

Add a text template to your solution.

To create a text template

  1. Build the solution and start running it in the debugger. (On the Build menu, click Rebuild Solution, and then on the Debug menu, click Start Debugging.) A new instance of Visual Studio opens the Debugging project.

  2. Add a text file named DebugTest.tt to the Debugging project.

  3. Make sure that the Custom Tool property of DebugTest.tt is set to TextTemplatingFileGenerator.

Debugging directives that access a model from a text template

Before you can access a model from the statements and expressions in a text template, you must first call a generated directive processor. Calling the generated directive processor makes the classes in your model available to the text template code as properties. For more information, see Accessing Models from Text Templates.

In the following procedures, you will debug an incorrect directive name and an incorrect property name.

To debug an incorrect directive name

  1. Replace the code in DebugTest.tt with the following code:

    Note

    The code contains an error. You are introducing the error in order to debug it.

    <#@ template language="C#" inherits="Microsoft.VisualStudio.TextTemplating.VSHost.ModelingTextTransformation"#>
<#@ output extension=".txt" #>
<#@ modelRoot processor="DebuggingTestLanguageDirectiveProcessor" requires="fileName='Sample.ddd'" provides="ExampleModel=ExampleModel" #>

Model: <#= this.ExampleModel #>
<#
foreach (ExampleElement element in this.ExampleModel.Elements)
{
#>
    Element: <#= element.Name #>
<#
}
#>

  2. In Solution Explorer, right-click DebugTest.tt, and then click Run Custom Tool.

    The Error List window displays this error:

    The processor named 'DebuggingTestLanguageDirectiveProcessor' does not support the directive named 'modelRoot'. The transformation will not be run.

    In this case, the directive call contains an incorrect directive name. You have specified modelRoot as the directive name, but the correct directive name is DebuggingTestLanguage.

  3. Double-click the error in the Error List window to jump to the code.

  4. To correct the code, change the directive name to DebuggingTestLanguage.

    The change is highlighted.

    <#@ DebuggingTestLanguage processor="DebuggingTestLanguageDirectiveProcessor" requires="fileName='Sample.ddd'" provides="ExampleModel=ExampleModel" #>

  5. In Solution Explorer, right-click DebugTest.tt, and then click Run Custom Tool.

    Now the system transforms the text template and generates the corresponding output file. You will not see any errors in the Error List window.

To debug an incorrect property name

  1. Replace the code in DebugTest.tt with the following code:

    Note

    The code contains an error. You are introducing the error in order to debug it.

    <#@ template language="C#" inherits="Microsoft.VisualStudio.TextTemplating.VSHost.ModelingTextTransformation"#>
<#@ output extension=".txt" #>
<#@ DebuggingTestLanguage processor="DebuggingTestLanguageDirectiveProcessor" requires="fileName='Sample.ddd'" provides="ExampleModel=LibraryModel" #>

Model: <#= this.ExampleModel #>
<#
foreach (ExampleElement element in this.ExampleModel.Elements)
{
#>
    Element: <#= element.Name #>
<#
}
#>

  2. In Solution Explorer, right-click DebugTest.tt, and then click Run Custom Tool.

    The Error List window appears and displays one of these errors:

    (C#)

    Compiling transformation: Microsoft.VisualStudio.TextTemplating<GUID>. GeneratedTextTransformation' does not contain a definition for 'ExampleModel'

    (Visual Basic)

    Compiling transformation: 'ExampleModel' is not a member of 'Microsoft.VisualStudio.TextTemplating<GUID>.GeneratedTextTransformation'.

    In this case, the text template code contains an incorrect property name. You have specified ExampleModel as the property name, but the correct property name is LibraryModel. You can find the correct property name in the provides parameter, as shown in the following code:

    <#@ DebuggingTestLanguage processor="DebuggingTestLanguageDirectiveProcessor" requires="fileName='Sample.ddd'" provides="ExampleModel=LibraryModel" #>

  3. Double-click the error in the Error List window to jump to the code.

  4. To correct the code, change the property name to LibraryModel in the text template code.

    The changes are highlighted.

    <#@ template language="C#" inherits="Microsoft.VisualStudio.TextTemplating.VSHost.ModelingTextTransformation"#>
<#@ output extension=".txt" #>
<#@ DebuggingTestLanguage processor="DebuggingTestLanguageDirectiveProcessor" requires="fileName='Sample.ddd'" provides="ExampleModel=LibraryModel" #>

Model: <#= this.LibraryModel #>
<#
foreach (ExampleElement element in this.LibraryModel.Elements)
{
#>
    Element: <#= element.Name #>
<#
}
#>

  5. In Solution Explorer, right-click DebugTest.tt, and then click Run Custom Tool.

    Now the system transforms the text template and generates the corresponding output file. You will not see any errors in the Error List window.