fat models aren't enough - railsconf

8/3/2019 Fat Models Aren't Enough - RailsConf

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Fat ModelsArent Enough

Jeff Casimir / @j3

learn by doing

Tuesday, May 17, 2011


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Best Practices

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Refactoring by Hamlet DArcy

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Refactoring by Hamlet DArcy

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Don't touch anything that doesn't

have[good test]coverage.

Otherwise, you're not refactoring;you're just changingshit.



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4

Question, Object, & Suggest



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Skinny Controllers,Fat Models

Jamis Buck, October 2006



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When first getting

started with Rails,it is tempting to

shove lots of

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logic in the view.



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A better way is to

move as much of thelogic as possible

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into the controller.



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If we push that code

into the model, we...

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slim down

the controller

document the

operation by namingthe method



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9The Rails Stack



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9The Rails Stack



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BeautifulViews are HTML

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BeautifulActions are 8 simple lines

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Beautiful Models are Organized

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Fat Models Arent Enough

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Why

Bother?

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Ideas for discussion

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Ideas for discussion

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Presenter Pattern

Better Rails throughBetterRuby



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The Presenter Pattern



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Presenter Pattern, Formally

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Presenter Pattern, Formally

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Adaptation of the

Decorator Pattern

Wrapper that adds

non-mutator

methods



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Presenter Pattern, As I See It

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Presenter Pattern, As I See It

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Object-based

shepherd of

presentation

Understands themixing of one or

more objects



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19In Need of a Presenter

/app/controllers/reports_controller.rb

/app/views/reports/show.html.haml



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201a. Build Presenter

/app/presenters/student_report.rb



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attr_reader:student, :term, :report_type



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211b. Use the Presenter





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222b. Presenter as Engine




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b D f E i


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232b. Defer to Engine


- @report.courses.each do |course|- course_report [email protected]_data_for_course(course)

= render:partial => "course_report", :locals =>{:course_report => course_report}


2b D f E i


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- @report.courses.each do |course|- course_report [email protected]_data_for_course(course)

= render:partial => "course_report", :locals =>{:course_report => course_report}

= render:partial => 'course_report',:collection => @report.course_reports


2b D f E i


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= render:partial => 'course_report',:collection => @report.course_reports


2b D f t E i


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= [email protected]_reports

Asks each element for its ClassName

Renders the partial with that name andsets the local variable


3 C t i E i


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243a. Compute in Engine



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defcourse_reportscourses.collect do |c|

end end

end

@student.report_data_for_course(c)


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end end

end



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end end

end

defreport_data_for_course(course) # Compute the report data end



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end end

end

defreport_data_for_course(course) # Compute the report data end

report_data_for_course(c)


4 C i l D t


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254. Canonical Data



@report.name

"#{@report.last_name}, #{@report.first_name}""#{@report.report_title} for #{@report.start_date} to#{@report.end_date}"


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254. Canonical Data



@report.name

"#{@report.last_name}, #{@report.first_name}""#{@report.report_title} for #{@report.start_date} to#{@report.end_date}"

defstudent_name[last_name, first_name].join(", ")

end


4 C i l D t


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254. Canonical Data



@report.name

"#{@report.report_title} for #{@report.start_date} to#{@report.end_date}"


end

@report.student_name


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deftitle "#{report_title} for #{start_date} to #{end_date}" end

254. Canonical Data



@report.name

"#{@report.report_title} for #{@report.start_date} to#{@report.end_date}"


end



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deftitle "#{report_title} for #{start_date} to #{end_date}" end

254. Canonical Data



@report.name


end


@report.title

Or maybe a decorator?


5 End State Review


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265. End State Review


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5 End State Review


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5 End State


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275. End State


5 End State


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275. End State

/app/presenters/student_report.rb (rst half)


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285. End State

/app/presenters/student_report.rb (second half)


5 End State


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285. End State

/app/presenters/student_report.rb (second half)


Afterthoughts


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29Afterthoughts


Afterthoughts


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29

Did you just obliterate MVC?

Afterthoughts


Afterthoughts


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Why not just use helpers?

Afterthoughts


Afterthoughts


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They suck

Afterthoughts


Afterthoughts


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They suck

Objects are not scary

Afterthoughts


Afterthoughts


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They suck

Objects are not scary

Using Rails helpers is ok!

Afterthoughts



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Better Rails throughBetter Ruby



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A significant percentage of

Rails programmers are not

Ruby programmers.

(my theory)

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Dont RepeatYourself (DRY)



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Dont copy and paste code.


Dave Thomas & Andy Hunt



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Every piece of knowledge must have a single,

unambiguous, authoritative representation within a system.


Dave Thomas & Andy Hunt


33Real-World DRY: Sort


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33Real World DRY: Sort

Typical Param-Handling Action




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Typical Param-Handling Action




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Simple DRY Improvement




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class StudentsController < ApplicationControllerdefindex

@students=Student.all_by(params[:sort_by]) endend




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Real DRY Progress

class StudentsController < ApplicationControllerdefindex

@students=Student.all_by(params[:sort_by]) endend

class Student < ActiveRecord::Base defself.all_by(param) case param when"last_name"then order(:last_name) when"first_name"then order(:first_name) else order(:id) end

endend Thinking about scope?

Give me a minute.


36Real-World DRY: Setters


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36Real World DRY: Setters




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Action Setting Attributes




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class StudentsController < ApplicationControllerdefcreate

@student=Student.new(params, current_user) # redirects, etcend

end




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Trying to Encapsulate Creation


@student=Student.new(params, current_user) # redirects, etcend

end

class Student < ActiveRecord::Base definitialize(params, creator) self.created_by = creator self.lunch_id =LunchTracker.new self.lunch_balance =LunchTracker::STARTING_BALANCE super

endend




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Build Through the Relationship


@student= current_user.students.new(params) # redirects, etcend

end




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Build Through the Relationship



end

class Student < ActiveRecord::Base definitialize(params = nil) self.lunch_id =LunchTracker.new self.lunch_balance =LunchTracker::STARTING_BALANCE super endend



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Single Responsibility Principle

39


E bj t h ld


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Single Responsibility Principle

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Every object should

have a single

responsibility, and

that responsibility

should be entirelyencapsulated by

the class.




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40ea o d Se e s

SRP Cleanup

class Student < ActiveRecord::Base definitialize(params = nil) self.lunch_id =LunchTracker.new

super end

end

self.lunch_balance =LunchTracker::STARTING_BALANCE




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SRP Cleanup


super end

end





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0

SRP Cleanup


super end

end





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SRP Cleanup


super end

end




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More Repetition

class Student < ActiveRecord::Base definitialize(params=nil)

super endend

self.lunch_id =LunchTracker.new




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More Repetition

class Student < ActiveRecord::Base

definitialize(params=nil)

super

endend

has_one:lunch, :class_name => 'LunchTracker'





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More Repetition



super

endend






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More Repetition



super

endend


self.build_lunch




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Start / End Review


@student=Student.new(params[:student]) @student.created_by = current_user @student.lunch_id =LunchTracker.new @student.lunch_balance =0

# redirects, etcend

end




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end

class Student < ActiveRecord::Base has_one:lunch, :class_name => 'LunchTracker'definitialize(params = nil)

self.build_lunch super endend

Start / End Review



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Signs of SRP Violations 43



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Signs of SRP Violations

Methods that do too much

Symptom:Your method is longer than 8 linesSolution: refactor with extract method

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Methods located in the wrong object

Symptom: reaching too deeply into child objects / Law of Demeter

Solution: refactor with move method

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Methods located in the wrong object

Symptom: reaching too deeply into child objects / Law of Demeter

Solution: refactor with move method

Magic Numbers, copy text, and configuration data

Solution: introduce constants or a config object

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Scopes are Dead



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Why We Loved Scopes 45



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Simple Scope in Rails 3 46



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Simple Scope in Rails 3 46

Quick and Easy



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A Gotcha Scenario 47



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Frank creates a migration adding the

inactive field to Student

Frank writes a scope like this:scope :active, where(:inactive => false)

Frank checks in his code, woohoo!

Lucy checks out Franks code

Lucy runs rake db:migrate



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Frank creates a migration adding the

inactive field to Student

Frank writes a scope like this:scope :active, where(:inactive => false)

Frank checks in his code, woohoo!

Lucy checks out Franks code

Lucy runs rake db:migrate

fixedin

3.0.2+



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Scope with Parameters 48



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Scope with Parameters 48

Lambda ZOMG!



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AREL and Lazy Evaluation 49



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Scopes & Lambdas 50



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Scopes & Lambdas 50


We dont need scopes,


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We don t need scopes,

just write good Ruby. 51


We dont need scopes,


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We don t need scopes,

just write good Ruby. 51

Class Methods > Scopes


52Wrap Up


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52Wrap Up


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Use presenters as an abstraction layer between views

and models

DRY isnt about copy & paste, its about knowledge

Forget scopes, you dont need them!

Embrace Ruby

Jeff Casimir

@j3

learn by doing


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Writing Better Instructions

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Every instruction


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Writing Better Instructions

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y

added is technical

debt accumulated.



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Less code is less debt 55



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Less code is less debt

self is rarely necessary

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return is rarely necessary

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Master collection operations including:each, collect/map, select, detect, merge

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Master collection operations including:each, collect/map, select, detect, merge

Take advantage of return values from all statements, evenif, case, while

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Method Naming 56



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Method Naming

Names matter

Express meaning, imply the return type and quantity

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Method Naming

Names matter


Follow Ruby naming conventions

Solutions: if it changes the data, end in !

if it returns a boolean, end in ?

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Method Naming

Names matter


Follow Ruby naming conventions

Solutions: if it changes the data, end in !

if it returns a boolean, end in ?

Physically organize methods within a model...

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57Collecting Class Methods


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class Student class


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class Student class

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