SharpDevelop 4.2 now supports SubSonic T4 templates. Subsonic is an open source object-relational mapper and makes use of T4 templates in all but one of its supported methods to provide access to your data. Before we take a look at what new T4 features were added to SharpDevelop to support SubSonic let us see what you need to do to get everything working.

Using SubSonic T4 Templates with SharpDevelop

In order to use the SubSonic T4 templates with SharpDevelop you need to make two modifications to the Settings.ttimport file.

Replace the EnvDTE assembly reference:

<#@ assembly name="EnvDTE" #>

With the following:

<#@ assembly name="$(addinpath:ICSharpCode.PackageManagement)PackageManagement.dll" #>

This references SharpDevelop's NuGet addin assembly which implements its own version of the Visual Studio object model.

Add a new import directive as shown below:

<#@ import namespace="EnvDTE = ICSharpCode.PackageManagement.EnvDTE" #>

This creates a namespace alias for EnvDTE so the references to the Visual Studio object model in the SubSonic T4 template will work.

All that is left now is to save the changes made to the Settings.ttimport file and generate the database access code by executing the ActiveRecord.tt, Context.tt and Struct.tt T4 templates. This can be done by right clicking them in the Projects window and selecting Execute Custom Tool.

Now we will take a look at the new features that made this possible.

Referencing SharpDevelop Properties and Environment Variables in T4 Templates

The T4 assembly and include directives now support the $(PropertyName) syntax to use SharpDevelop properties such as SolutionDir and ProjectDir.

<#@ assembly name="$(ProjectDir)lib\MyLibrary.dll" #> 
<#@ include file="$(SolutionDir)Templates\MyTextTemplate.tt" #> 

The assembly and include directives also support environment variables through the %EnvironmentVariableName% syntax.

<#@ assembly name="%ProgramFiles%\lib\MyLibrary.dll" #> 
<#@ include file="%HOMEPATH%\MyTextTemplate.tt" #>

This new feature also supports the addinpath property and is used to allow a T4 template to reference SharpDevelop's NuGet addin using the $(addinpath:AddIn-ID) syntax which is expanded to the directory containing the addin.

Accessing the SharpDevelop IDE from a T4 Template

The SubSonic T4 templates use the Visual Studio object model to find the project's app.config file and read the database connection string stored here in order to access your database. To support this the T4 templating host in SharpDevelop now implements the IServiceProvider interface which allows you to access SharpDevelop's implementation of the Visual Studio object model.

To access the Visual Studio object model you set the T4 template so it is host specific:

<#@ template language="C#" hostspecific="true" #>

Then you can access the DTE object, which is the top-level object of the Visual Studio object model, as shown below.

<#
    IServiceProvider provider = (IServiceProvider)Host; 
    EnvDTE.DTE dte = (EnvDTE.DTE)provider.GetService(typeof(EnvDTE.DTE));
#>

The Visual Studio object model is not fully implemented in SharpDevelop so you may run into problems if you make extensive use of this object model.