Where do I put my Business Logic?

Antonio de la Torre@adelatorrefoss

March 28th 2014

Grails is not my Domain Model

Antonio de la Torre@adelatorrefoss

Engineer & Agile Coach @ KaleidosMadrid, Spain

Me

A lot of questions&

one Proposal

1st. step

All code inside Controller

Scaffolding helps

Common methods

MVC&

Skinny ControllerFat Model

2nd. step

Move to Domain Model

Extra large User

God Object&

Services layer

3rd. step

Move to Services

And now XXL Services

Anemic Model&

Transaction Script

Problems

Service with too muchresponsibility

1.- in Creationcomplex objects, constraints and invariants

2.- too much invocationsa lot of injected services, no separation

3.- how to save()?addTo, hstore, GORM, mongo, ...

Persistence is a Hardware problem

No OOP

We implement behaviour in Agile

Where is our Business Logic?

but …

here it is ...

How looks like our unit tests?

mocks & stored data

Actions

Actions

Single Responsibility Principle (SRP)

SOLID

Tell, don’t ask

“Object Calisthenics. 9 steps to better SW design” , Jeff Bay

GRASP

… are all smells

OOP?

What about FP?

Functional Programming

- Inmutability- Transaction scripts- Stateless services- Stateless API- Rare workflows … - Objects with state… but we don’t usually use them

“Why OO in web, when usually is DB -> Object -> Process -> Object -> DB”Functional Programming for the Object-Oriented Programmer Brian Marick

So better if we useAgnostic Patterns

Domain Driven Designby Eric Evans

DDD

“The goal of domain-driven design is to create better software by focusing on a model of the domain rather than the technology”

Tackling complexity

DDD is a way of dealing with complexity.

Complex is easy. Simple is a lot harder.

Ubiquitous Language

“A language structured around the domain model and used by all team members to connect all the activities of the team with the software”

DDD leads to Model Driven Design

Test your model

Behaviour centric

Layered Arquitecture

Diagram

Entities

“When an object is distinguished by its identity, rather than its attributes, make this primary to its definition in the model”

Value Objects

“When you care only about the attributes of an element of the model, classify it as a VALUE OBJECT. Don’t give it any identity…”

Services

“When a significant process or transformation in the domain is not a natural responsibility of an ENTITY or VALUE OBJECT, add an operation to the model as a standalone interface declared as a SERVICE. Make the SERVICE stateless.”

Modules

“Choose MODULES that tell the story of the system and contain a cohesive set of concepts.”

Aggregates

“Cluster the ENTITIES and VALUE OBJECTS into AGGREGATES and define boundaries around each. Choose one ENTITY to be the root of each AGGREGATE, and control all access to the objects inside the boundary through the root. Allow external objects to hold references to the root only.”

Factories

“Shift the responsibility for creating instances of complex objects and AGGREGATES to a separate object, which may itself have no responsibility in the domain model but is still part of the domain design.”

Repositories

“For each type of object that needs global access, create an object that can provide the illusion of an in-memory collection of all objects of that type.”

Implementing

Implementing Entities

These are Domain Classes in Grails. They come with persistence already resolved through GORM.

hasOne vs. belongsTo property can be used to define the lifecycle of entities and their relationships.

Implementing Value Objects

In Grails, you can use “embedded” property in GORM field to manage a value object.

And deal with them with POGO or Command Objects

Implementing Services

With our Services in Grails● Dependency Injection● Transaction support

Implementing Modules

Grails plug-in mechanism.

Implementing Aggregates

Aggregates are implemented in the hasMany - belongsTo relationship.Can control the root access within a Service.

Implementing Factories

Implement Factories classes to create new instances with an abstract interface… It could be configurable with properties.

Implementing Repositories

Grails Service can be used to implement a dedicated Repository object that simply delegates its operation to Grails GORM.

All together

All together …

In a more complex Aggregation, create a service to manage, this service acts as a Repository. Control invariants.

To access a simple Entity use GORM.In a Domain Model with hasOne and belongsTo can act as an Aggregate Root, and use GORM directly.

And we reserve Factories to instantiate external providers, like email service, S3 access, push mobile notifications, and so on …

In code ...

Model your domain, create your business logic, and separate it from your infrastructure.

ResourcesDomain Driven Design

Eric Evans

http://www.slideshare.net/thinkddd/domain-driven-design-dddsydney-2011

- (Intro) Complex vs Simple

http://pragprog.com/articles/tell-dont-ask

- Tell, don't ask

http://juan-garcia-carmona.blogspot.com.es/2012/11/solid-y-grasp-buenas-practicas-hacia-el.html

- SOLID

- Spanish

http://www.martinfowler.com/bliki/AnemicDomainModel.html

- Anemic Model

Resourceshttp://www.slideshare.net/sergiopolo/introduccin-a-ddd

(Spanish)

- Building Blocks

http://www.slideshare.net/harshjegadeesan/domain-driven-design-presentation

STARRED- Intro

- Building Blocks

http://www.slideshare.net/GlenWilson/domain-driven-design-pattern-summaries-presentation

- Extense document with Pattern Summaries

http://www.slideshare.net/ziobrando/taming-complex-domains-with-domain-driven-design-presentation

STARRED!!- Building Blocks

- Large Scale DDD

Resourceshttp://www.slideshare.net/DimkaG/domain-driven-design-and-model-driven-development- ideas to implement the building blocks.

http://blog.refactoringin.net/2011/08/17/grails-as-a-ddd-platform/- Unique reference directly with Grails- Repository??? with GORM…

Brian Marick - Functional Programming for the Object-Oriented Programmerhttps://leanpub.com/fp-oo

http://www.mabishu.com/blog/2012/12/14/object-calisthenics-write-better-object-oriented-code/Object Calisthenics Write Better OO Code

Javier Acero - Mi dominio es mio y no lo compartohttp://vimeo.com/69157481(Spanish)