Aki Salmi: Object Oriented Views at I T.A.K.E. Unconference 2015

Object Oriented
Views
Aki Salmi
@rinkkasatiainen
Wednesday, May 20, 15

Programmer
@Ambientia
skype: @rinkkasatiainen
twitter: @rinkkasatiainen
email: aki.salmi@iki.ﬁ

Content
• Background
• A way to solve
• Discussion
• Open Space: Mob Programming?

Very Brief Background
• Conﬂuence plugin

We have all seen

Controllers like

/INDEX
(1 of many actions)
Params
Service
“DAO”
“or not DAO”
DAO-DAO-DAO
Service
Service
Domain
Service
Render

Not that, not today

Let’s assume we’re
working with thin
controllers

Have we seen

views like

this
Only today: logic in a view

So how then?

How about Code I’ve
written myself?

Not much better

A Deeper Dive
Params
BUILD
CONTEXT
GET MODEL
RENDER
OR RENDER

But there is a catch

Render Many Blogs
Or 1, or 0

... based on object
types

Build a ‘different’
domain entity?
Build
‘real’
Domain
Build
‘real’
Domain

Build a ‘different’
Context
BUILD
context
Diff
context
no
context

Render ‘different’
template
Templ_0
Templ_1
Templ_n

Seems like a
violation of SRP
(Single Responsibility Principle)

What did we see
• build parameters
• build context (on 2 places)
• build domain
• render different data, differently, based
on the domain entity

Visually
Controller
HTTP GET
Domain
View 0 View 1 View N

It works

..sort of
• most of the bugs I introduced, were on
this behavior of the system.
• This class
• Concepts introduced by this class
• Integration with Conﬂuence API
• especially ‘null’s

What IF
Controller
HTTP GET
Domain
View 0 View 1 View N

What IF...
C’s responsibility
• Given a set of parameters...
• Build Model (service / repository)
• Render Template with model given
• and let other’s to ﬁgure out which
template to render

Decorate / Exhibit
Controller
HTTP GET
Domain
View
Exhibit
1) build model
2) render
3) exhibit
View tmpl
4) render

How does it work

few design decision
done by me
• avoid nulls
• separate Read Model from Write Model
• 1st class collections
• Separated Query and Command
Controller (sort of CQRS)

Domain Entity: Group
<if> ReadOrWriteModel
<if> ReadModel <if> WriteModel
GroupEntity GroupDescrGroupList

GroupEntity
* immutable
* ﬁnal private prop
* behavior rich
GroupDescriptor
* public properties
* tiny behavior
AGroupThatDoes
NotExistYet
AGroup

GroupList
* behavior: iterate

Introducing Exhibits
• Introduced by Avdi Grimm
• sort of presenter-decorator

Exhibit Characteristics
• Wraps a single model instance
• Is a true Decorator
• Brings together model and context
• Encapsulates the decision about how to
render an object
• May modify the behavior of an object

Exhibit B
Exhibit A
Exhibit visually
Model object

Exhibits: Group
<if> Exhibit
+ renderBody()
GroupListExh GroupList
GroupExhibit
GroupEntity
EditGroupExh GroupDesc
GroupWPicture

Exhibits: Group
GroupListExh ListView
GroupExhibit ShowGroup
EditGroupExh GroupDesc
GroupWPicture ShowGPicture

REST view
HTTP PATH Contr#Action Domain Class
GET /foo(.:format) foos#index FooList
POST /foo(.:format) foos#create FooDescriptor
GET /foo/new foos#new FooDescriptor
GET /foo/:id/edit foos#edit FooDescriptor
GET /foo/:id foos#show FooEntry
PATCH/PUT /foo/:id foos#update FooDescriptor
DELETE /foo/:id foos#delete FooDescriptor

Creating exhibits
public exhibit(ReadWriteModel model){
for_each( exhibit: exhibit_classes ){
if( exhibit.applicableTo( model )
// wrap model to exhibit and
serve exhibit as new model
}
}

Creating exhibits
the ruby way 1/2
Avdi Grimm: Object on Rails, Listing 77

Creating exhibits
the ruby way 2/2
Avdi Grimm: Object on Rails, Listing 77

Creating exhibits
the Java 8 way 1/N

Time for some code
Confluence plugin
Velocity templates

Controller

Exhibit A

Exhibit B

Exhibit C

Exhibit D

And visually

Surroundings
Exhibit templates

RemotePictureExhibit ||
DefaultPictureExhibit
UserProﬁleExhibit
Could be composite

Did it work -
in retrospect
• No issues in production with this code
• It is not, by far, easy to grasp. Without
someone explaining

What I did not show
• transformations of domain entities:
• Request -> Write -> Persistence
• Persistence -> Write (-> Read)
• Composite Exhibit - how to show 0, 1 or
many concepts, dynamically, based on
the ModelObject rendered

What could I experiment
• Capabilities for exhibits
• Capability.mobile
• Capability.REST
• Capability.json

Thanks!
Questions?
skype: @rinkkasatiainen
twitter: @rinkkasatiainen
email: aki.salmi@iki.ﬁ

Aki Salmi: Object Oriented Views at I T.A.K.E. Unconference 2015

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