Domain Specific Development using T4

Editor's Notes

• #3: Main concepts of DSD Demo project features
• #5: 1) A task/project/problem in hand 2) Pick favorite general purpose language – C#, VB.NET 3) Deliver project Each occurrence of problem has many aspects that are the same everytime (fixed part) And other aspects that are differs each time – variable part We’re going to automatically generate code for the variable part of the solution. Fixed part – We’ll treat as the framework Variable aspect – fits into the framework itself On a current project: Fixed aspect: Web Asset and configuration management framework Variable aspect: The content models (or aka content types in SharePoint) The content types: defined as metadata in a database, configuration file etc. T4 templates run to generate special classes (and logic) for the specific content types. The generated code could then be embedded in VS.NET projects (code or assembly) or called dynamically on the server to retrieve data. Other examples: ORM software Language-oriented programming Basis – observation Instead of solving problem one-at-a-time Many problems can more easily be resolved by designing a special-purpose language Code generation – through DSL toolkit with VS.NET Use T4 to generate that specialized programming language
• #6: 1) A task/thought/problem in hand 2) Create/Pick a special-purpose language 3) Use a general purpose lang to write framework 4) Deliver project
• #7: -- Benefits Ability to work in terms of the problem space Working in terms of the model of the problem space makes it more accessible to people not familiar with the problem space You can have the domain-experts verify the correctness of your model independently The model itself should be more testable and used to simulate scenarios Once the business knowledge is captured, the DSL could be updated to use other technologies, for example, by modifying the generator
• #8: Framework – use general-purpose languages The variable pieces –generate domain-specific languages Plug the generated domain-specific languages into the framework
• #9: DSL = “custom language that targets a small problem domain, which it describes and validates in terms native to the domain.” Could be seen as a set of tools to build tools Focus: text-based only!
• #10: T4 - Engine to create text-based DSLs Visual Studio.NET 2005 - GAT toolkits 2008 - Downloadable DSL toolkit 2010 - Integrated part
• #11: Generates code from described models Models could be Metadata Configuration Database What does it stand for? What are the Inputs? What are the outputs? What does the syntax look like? What are the supported languages?
• #19: T3 == Text-to-Text Transformation T4 == Text Template Transformation Toolkit A tool in the VS.NET DSL toolkit A text-based code generation engine Templates = syntax similar to ASPX or ASCX Support: C# and VB.NET
• #20: VS.NET extensibility
• #22: .tt Pre 2010 – text file – turn it into .tt 2010 – two kinds of item templates Default transformation tools – properties of a tt file Publishing: Build Action to Content
• #23: ASP.NET-like syntax Processor directives: compilation options Blocks: Mixture of text, control logic, blocks of executable code
• #24: Base class: Microsoft.VisualStudio.TextTemplating.TextTransformation Directives Assemblies are loaded Include files are imported Text and expression blocks: Copied to the TransformText method Class-feature blocks: Copied at the class level T4 engine – calls the “TransformText” method – entry point %TEMP% folder
• #25: This demo will be the basis for all Syntax reviewed here.
• #27: Provide instructions to the T4 engine Just like ASPX pages: <#@ and end with #> Directives template assembly import output include
• #28: Characteristics of the transformed output Debug --- true/false True – you can take a look files in system %TEMP% folder Language: Values: C#, VB, C#3.5 Inherits Base class: Microsoft.VisualStudio.TextTemplating.TextTransformation Tells which base class to use Hostspecific --- true/false Mostly used to output template file name to the transformed file Host.TemplateFile Host.StandardAssemblyReferenes
• #29: “Add reference” in VS.NET One parameter name could be an assembly in the GAC <#@ assembly name=“System.Data” #> or absolute path to the assembly <#@ assembly name=“c:\projects\proj1\bin\debug\proj1.dll” #>
• #30: Equivalent to: C# using VB.NET import One parameter namespace
• #31: File to be included verbatim in template One parameter File Can contain any of the valid T4 constructs Relative paths -- to the main template
• #33: Had an overview of the processing directives Let’s talk about T4 block types
• #34: Just type directly into the .tt file Copied directly to TransformText method %TEMP% Show generated file
• #35: Control the flow of processing in TransformText method Example usage: To conditionally output Text blocks Iterate over data and output things conditionally
• #36: Use to add strings to the output file Added, in sequence To the “TransformText” method with calls to the ToString() method Used in cases to change some aspect of the generated output text file to use Calculated values External data e.g. database column values some other calculated value in a Statement block somewhere else in the .TT file.   C# – could be multiple lines VB.NET – single lines only
• #37: Any class-level construct Helper functions Fields Constants Properties any construct that is valid at the class level T4 allows the usage of text and expression blocks intermingled with class feature blocks The helper method would be called from within a Statement block.
• #39: Text template - %TEMP% Preprocessed: uses TextTemplatingFilePreprocessor transformation tool Debugging: System.Diagnostics.Debugger.Launch();
• #45: DO NOT REMOVE THIS SLIDE