Fluent Validation Framework - A DSL for validations using fluent interfaces

Overall presenta3on  Introduc3on to Domain Speciﬁc Languages and  its techniques. As well as showing Fluent  Valida3on Framework concep3on process.   www.devoxx.com 

Domain Speciﬁc Language (DSL) is a  programming language dedicated to  solve problems of an speciﬁc domain  www.devoxx.com 

which can be technical    SQL   HQL   CSS  www.devoxx.com 

or business related.   Banking   Manufacturing   Logis3cs  www.devoxx.com 

A DSL can be internal or external.  www.devoxx.com 

External DSLs are self‐contained  www.devoxx.com 

while internal DSLs remain on top of  other programming languages.  www.devoxx.com 

In other words, internal DSLs are APIs.  www.devoxx.com  That's why they're also known as Fluent Interfaces! 

DSLs allow you to express domains clearly.  www.devoxx.com 

For example, while a business analyst of  a banking domain would say  Transfer 5.000,00 from Client A's cash account to Client B's savings account.  www.devoxx.com 

A common JAVA implementa3on could be  bankService.transfer(5000.00, clientA.getCashAccount(), clientB.getSavingsAccount());  www.devoxx.com 

An external DSL could express the same as  transfer 5000 from clientA.cashAccount to clientB.savingsAccount  www.devoxx.com 

And an internal DSL in JAVA could look like  bankService.execute( new Transfer() .of(5000) .from(clientA.cashAccount()) .to(clientB.savingsAccount()));  www.devoxx.com 

It’s not about one single method  public Transfer of(double value);  www.devoxx.com 

but an en3re meaningful opera3on.  new Transfer() .of(5000) .from(clientA.cashAccount()) .to(clientB.savingsAccount()) www.devoxx.com 

Some techniques to deﬁne internal DSLs  www.devoxx.com 

Method Chaining  new Transfer() .of(5000) .from(clientA.cashAccount()) .to(clientB.savingsAccount()) www.devoxx.com 

Nested Func3on  bankService.transfer(5000, from(clientA.cashAccount()), to(clientB.savingsAcount())); www.devoxx.com 

Object Scoping  bankService.execute( new Transfer(){{ of(5000); from(clientA.cashAccount()); to(clientB.savingsAccount()); }}); www.devoxx.com 

Fluent Valida3on Framework is a lab  project applying Fluent Interfaces to the  domain of code valida3on.  www.devoxx.com 

Main idea was changing valida3ons like  if(arg0 == null) throw new IllegalArgumentException(); www.devoxx.com 

to something like  ensure(arg0).isNotNull(); www.devoxx.com 

How to change excep3on message?  ensure(arg0).isNotNull().otherwise("arg0 cannot be null"); //doesn't work www.devoxx.com 

Trigger method at the end of the expression  ensure(arg0).isNotNull().now(); ensure(arg0).isNotNull() .otherwise() .throwThis( new IllegalStateException()) .now(); //not cool! www.devoxx.com 

Another op3on was crea3ng two entry points  ensure(arg0).isNotNull(); analyse(arg0).and().throwThis(new IllegalStateException()).ifNull(); www.devoxx.com 

Mixing method chaining with nested func3ons  ensure(myObject).is(inValidState()); analyse(systemReport).and(notifyByEmail()).ifIsNot(operatingWell()); www.devoxx.com  the solu3on became extensible!  

Today we saw   DSLs are cool!   External DSLs are hard to implement   Fluent Interfaces and Internal DSLs are the same thing   Fluent Interfaces work great for extensively used APIs  www.devoxx.com 

That’s all folks!   project hXp://ﬂuval.sourceforge.net   blog hXp://blog.danielgazineu.com   email/gtalk danielgazineu@gmail.com   twiXer @danielgazineu  www.devoxx.com 

http://danielgazineu.com	46
http://blog.danielgazineu.com	44
http://www.slideshare.net	9

Fluent Validation Framework - A DSL for validations using fluent interfaces

by Daniel Gazineu on Nov 19, 2009

Accessibility

Categories

Tags

Upload Details

Usage Rights

3 Embeds 99

Statistics

Fluent Validation Framework - A DSL for validations using fluent interfaces — Presentation Transcript