APPLIED CODE GENERATION IN .NET

Dmytro Mindra Lohika, Odessa

What’s the matter ?

• We are engineers ! • Engineers’ time is valuable and expensive; • Engineers don’t like repetitive tasks;

Task classification

• Brains • Experience • Procedures

Houston, we’ve got a problem !

Our business domain contains 500+ entities.

Each entity needs CRUD.

Houston, we’ve got a problem !

And you have lots of time. The whole 4 months.

For your big team of 4 developers that should

not be a problem !

Houston, we’ve got a problem !

Oh, and we’re not sure which parts will stay generic and which won’t

Houston, we’ve got a problem !

Be agile, don’t wait for the analysts to finish their job, because we don’t have that kind of time.

Just change your code when the Requirements are

finished.

Houston, we’ve got a problem !

For each domain entity we should have • Stored Procedures • Repository • Service • Controller • Views • etc That’s about 1000 lines of code per entity.

Houston, we’ve got a problem !

But we have 500+ entities 500*1000 = 500000 lines of code. Who wants to type this in ?

Houston, we’ve got a problem !

• And when the changes arrive someone should make corrections to 500*1000 lines of code.

What are the solutions ? • Hand-code everything (and every change)

– Hire a lot of monkeys coders

• Design everything generically, correctly the first time – Mission impossible

• Use only code generation

– And spend your life changing generator to match all possible requirements

• Use combination of tools including code generation. – This seems reasonable

Boilerplate • Interestingly, the term (boilerplate) arose

from the newspaper business. Columns and other pieces that were syndicated were sent out to subscribing newspapers in the form of a mat (i.e. a matrix). Once received, boiling lead was poured into this mat to create the plate used to print the piece, hence the name boilerplate. As the article printed on a boilerplate could not be altered, the term came to be used by attorneys to refer to the portions of a contract which did not change through repeated uses in different applications, and finally to language in general which did not change in any document that was used repeatedly for different occasions.

CODE GENERATION is code that writes code

Some common terms

• Code generation • Automatic programming • Generative programming

IDE Generated Code Example

Tools evolution

Code Smith http://www.codesmithtools.com/

Demo

Generator

Code Generator

Input Output

Why CG? • Productivity • Quality • Consistency • Abstraction

PROS

• Code uniformity • Easy to debug • Easy to introduce huge changes • No more boilerplate code

CONS

• Someone should maintain the generator • Generator has learning curve • Generator usually has limitations

Applications • Database Access • Generate Test Data • Generate Integration Tests • User Interface • Documentation • Unit tests • File Formats • Web services • Business logic • DLL Wrappers • Firewall configuration • Website configuration • Looking for localizable strings

Code Generation is Fun ? • CG makes boring job for you

• Writing generator is fun

• Once written generator works for you

• You can experiment with different implementations by

modifying generator and regeneration the code.

• While writing the generator you get deeper into the technology instead of doing dull job.

Scaffolding and prototyping

• Code generation can help you to build fast prototypes.

MVC Scaffolding Demo

Rules

1. Give the proper respect to hand-coding 2. Handwrite the code first 3. Control the source code 4. Make a considered decision about the

implementation language 5. Integrate the generator into the development

process

Rules

6. Include warnings 7. Make it friendly 8. Include documentation 9. Keep in mind that generation is a cultural

issue 10. Maintain the generator

A note about DSL

A domain-specific language (DSL) is a programming language or specification language dedicated to a particular problem domain

Model Driven Architecture

Model Driven Architecture • Code generation has a dramatic impact on

development time and engineering productivity.

• The application is amenable to change on a large scale.

• The business rules are abstracted into files that are free of language or framework details that would hinder portability.

• The code for the application is of consistently high quality across the code base.

Benefits of MDA

• Quality • Consistency • A single point of knowledge • More design time • Design decisions that stand out

Software Factories

Industrializing Software Development

Software Factory

Consider this:

• Code generation has a large initial schedule overhead;

• Code generators are ideal for well-known large-scale problems;

• Code generation is powerful when used appropriately;

• Always keep in mind code generation limitations!

Code Generation Skills

• Text Templates • Regular Expressions • XML Parsing • Reflection

Show me the tools

Available tools

• StringBuilder • CodeSnippets • XSLT • Reflection Emit • EnvDTE • CodeDom • T4 • … (Python, Ruby,

StringBuilder

• Advantages – Almost all .net developers should feel comfortable using

the StringBuilder class so it requires no additional languages / tools to learn.

– Even with the disadvantages, the StringBuilder can be an excellent choice if you need to generate code quickly. Especially if you don’t need to maintain the “template” long term.

• Disadvantages – Unable to truly see the “template” within the control logic. – Requires a recompile if the “template” should be changed.

Code Snippets

• Advantages – Simple Xml based template with numerous

samples provided within Visual Studio. – Several open source code snippet libraries

available.

• Disadvantages – Limited snippet functions and at the present time

developers are unable to author additional snippet functions!

XSLT

• Advantages – Xml based template. – Simple code generation technique for those

developers comfortable with XSLT transformations.

• Disadvantages – While Xml is a relatively simple technology, XSLT

has been known to bring grown men to tears! – XSLT can be difficult to debug.

Reflection Emit

It is rocket science mixed with the black arts. • Full representation of physical structure • Allows building modules and assemblies at

runtime – Transient code only used at runtime – Persistent code for reuse

• Create classes, types and emit IL • Used by .NET compilers to build .NET apps • Can be as fast as normal code

EnvDTE

• EnvDTE is an assembly-wrapped COM library containing the objects and members for Visual Studio core automation.

• Using EnvDTE you can develop your own add-ins for Visual Studio that can generate code.

CodeDom • Advantages

– Allows a single “template” to generate code within several target languages, such as VB and C#.

– Additional language providers can be written to support other languages.

– Proven technology, used by Microsoft for code generation in all versions of Visual Studio since .net was released.

• Disadvantages – Unable to truly see the “template” within the control logic. – Requires a recompile if the “template” should be changed. – Very few developers have experience using the CodeDom

even though it has been with us since the .net framework 1.0.

Text Template Transformation Toolkit

How T4 Works ?

T4 Tools

• Tangible T4 Editor for Visual Studio 2010 RTM adds IntelliSense and Syntax Coloring to T4 Text Templates.

• T4 Toolbox

T4 Pros and Cons • Advantages

– Ability to embed C# control logic within the template. – Syntax that will be somewhat familiar to classic ASP developers.. – Preferred code generation technique for Entity Framework 4.0

and the Visual Studio 2010 modeling tools., which means lots of samples on MSDN, etc.

– Templates can be precompiled. • Disadvantages

– While third parties have written language support for Visual Studio no built in support for editing T4 templates exists in Visual Studio today.

– Relatively new technology, therefore not many developers have experience with T4 templates.

ReSharper 6.0 Code Generation

Create from Usage Generate Type Members Generate Type Constructor Generate Properties Generate Delegating Members Generate Formatting Members Generate Equality Members Implement/Override Methods

Some advices

Shall I Generate Interfaces?

Shall I Generate Interfaces?

No !

Shall I Unit Test generated code ?

• You shouldn’t unit test generated code. You may unit test generator instead.

Real World Case Studies

Case 1: Client – Server Communication

Existing API

Generated Server Proxy

Generated Client Proxy

Communication channel

Case 2: API Wrapper Le

gacy

API

Adap

ter Exist

ing

Appl

icat

ion

Case 3: Protocol Parser

Case 4: Model Driven DAL

Partially generated DB

Generated Entities

Generated Repositories

Hand written services

XML Model

It’s an Engineering, Baby ! Conclusion:

• Not a silver bullet but another good tool;

• Makes life easier when applied properly;

• Writing generator is much more fun than writing boilerplate code;

• Generated code is easier to debug;

• You can make huge changes in regenerated code easily;

Do try this !

• Code generation can make you flexible and responsive. Do try this at home. (Or at work)