Running T4 templates from other T4 template

What your probably looking for is T4 Toolbox. It will allow you to actually generate code in individual files and add them to a project automatically.

Highly Recommended.

I have used t4 toolbox to generate whole projects just based on a model.

(T4 Toolbox was formerly located at http://t4toolbox.codeplex.com/ but is now at https://github.com/olegsych/T4Toolbox )

We do this a lot. Here is an example how we reuse a common T4 template yet "pass parameters" into it:

<#
var currentUsername = "billclinton"; // this is for integration tests impersonating a user in our case
#>
<#@ include file="..\SomeTemplateThatIWantToReuseHere.tt" #>

And we keep our T4 template "generic" by dynamically determining the location that the T4 template is actually ran in (in this case, the T4 template that has the include line in it):

string namespaceName = code.VsNamespaceSuggestion();
var namespaceParts = namespaceName.Split('.');
var currentNamespaceLeg = namespaceParts.Last();

This allows us to do some very powerful templating without the need to duplicate our templates. The only thing being "duplicated" are our 4-line .tt files that have the include call in them, but these are pretty much maintenance free except whatever "configuration" we want to perform by passing in variables in the way we do it.

Yes, you can. This is how I'm doing it:

string templateText = File.ReadAllText(Host.ResolvePath(templateFileName));
Engine engine = new Engine();
string output = engine.ProcessTemplate(templateText, Host);
//this is optional - record all output to your file of choice:
File.WriteAllText(outputFilePath, output);