Handouts Slides Basic Rails

7/27/2019 Handouts Slides Basic Rails

1/25

CS169.1x Lecture 6:

Basic Rails"Fall 2012"

1"


2/25

The Database is Golden

Contains valuable customer datadont wantto test your app on that!

Rails solution: development, production andtest environments each have own DBDifferent DB types appropriate for eachHow to make changes to DB, since will haveto repeat changes on production DB?Rails solution: migrationscript describingchanges, portable across DB types


3/25

Migration Advantages

Can identify each migration, and know whichone(s) applied and when

Many migrations can be created to be reversibleCan manage with version controlAutomated == reliably repeatableCompare: use Bundler vs. manuallyinstall libraries/gemsTheme: dont do itautomate itspecifywhat to do, create tools to automate


4/25

Meet a Code Generator

rails generate migration CreateMovies

Note, this just creates themigration. We havent appliedit.

Apply migration to development:rakedb:migrate

Apply migration to production:heroku rakedb:migrateApplying migration also records in DB itselfwhich migrations have been applied

http://pastebin.com/

VYwbc5fq


5/25

Rails Cookery #1

Augmenting app functionality ==adding models, views, controller actions

To add a new modelto a Rails app:

(or change/add attributes of an existing model)

1.Create a migration describing the changes:rails generate migration(gives you boilerplate)

2.Apply the migration: rake db:migrate3.If new model, create model file app/models/model.rbUpdate test DB schema: rake db:test:prepare


6/25

An object representing an instance of a model

An object representing a table

Come on, it could be anything

An object representing a database

*

Based on what youve seen of Rails, what kind of object is likelybeingyielded in the migration code:def up

create_table 'movies' do |t|t.datetime 'release_date' ...

endend


7/25

Ted Codd

CRUD in SQL

Structured Query Language (SQL) is thequery language used by RDBMSsRails generates SQL statements atruntime, based on your Ruby code

4 basic operations on a table row:Create, Read, Update attributes, DeleteINSERT INTO users(username, email, birthdate)VALUES ("fox","[email protected]", "1968-05-12"),

"patterson", "[email protected]", "????")

SELECT * FROMusersWHERE (birthdate BETWEEN "1987-01-01" AND2000-01-01)

UPDATE users SET email = "[email protected]"WHEREusername="fox"

DELETE FROMusersWHERE id=1


8/25

The Ruby side of a model

Subclassing fromActiveRecord::Baseconnects a model to the databaseprovides CRUD operations on the modelDatabase table name derived frommodels name: Moviemovies

Database table column names are getters &setters for model attributes

Observe: the getters and setters do notsimply modify instance variables!

http://pastebin.com/ruu5y0D8


9/25

Creating: new save

Must call save orsave! on an AR modelinstance to actually save changes to DB

'!' version is dangerous: throws exception ifoperation failscreate just combines new and saveOnce created, object acquires a primary key(id column in every AR model table)ifx.id is nil orx.new_record? is true, x has neverbeen saved

These behaviors inherited fromActiveRecord::Basenot true of Ruby objects in general


10/25

Read: finding things in DB

class method whereselects objects based onattributesMovie.where("rating='PG'")

Movie.where('release_date < :cutoffand

rating = :rating',

:rating => 'PG', :cutoff=> 1.year.ago)Movie.where("rating=#{rating}") # BAD IDEA!

Can be chained together efficientlykiddie = Movie.where("rating='G'")

old_kids_films =

kiddie.where "release_date < ?", 30.years.ago


11/25

Read: find_*

find by id:Movie.find(3) #exception if notfoundMovie.find_by_id(3)# nil if not found

dynamic attribute-based finders usingmethod_missing:Movie.find_all_by_rating('PG')

Movie.find_by_rating('PG')Movie.find_by_rating!('PG')


12/25

Update: 2 ways

Modify attributes, then saveobjectm=Movie.find_by_title('The Help')m.release_date='2011-Aug-10'

m.save!Update attributes on existingobjectMovie.find_by_title('The Help').update_attributes!(

:release_date => '2011-Aug-10')

Transactional: either all attributes areupdated, or none are


13/25

def silly_fortune_2

self.fortune_text + 'in bed'

end

def silly_fortune_3

fortune_text + 'in bed'

end

They will all return a silly fortune

def silly_fortune_1

@fortune_text + 'in bed'

end

*

Assume table fortune_cookieshas column fortune_text

Which of these instance methods ofFortuneCookie "show", :controller=>"movies"}

params[:id]3

def show@movie =

Movie.find(params[:id])

end


17/25

What else can we do?

How about letting user return to movie list?RESTful URI helper to the rescue again:movies_path with no arguments links to Indexaction=link_to 'Back to List', movies_path


18/25

Only (C) is true

Only (A) and (B) are true

Only (A) and (C) are true

Only (A) is true

*

A) A route consists ofboth a URI and an HTTP method

B) A route URI must be generated by Rails URI helpers

C) A route URI may be generated by Rails URI helpers


19/25

Dealing with forms

Creating a resource usuallytakes 2 interactions

new: Retrieve blank formcreate: Submit filled formHow to generate/display?How to get values filled inby user?What to return (render)?


20/25

Rails Cookery #3

To create a new submittable form:1.Identify the action that gets the form itself2.Identify the action that receives submission3.Create routes, actions, views for eachIn form view, form element name attributescontrol how values will appear in params[]

Helpers provided for many common elements


21/25

Creating the Form

Anatomy of a form in HTMLthe action and methodattributes (i.e., the route)only namedform inputs will be submittedGenerating the form in Railsoften can use URI helper foraction, since its justthe URI part of a route (still need method)

form field helpers (see api.rubyonrails.org) generateconveniently-named form inputs


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22/25

Redirection, the Flash and the

Session(ELLS 4.7)

Armando Fox

2012 Armando Fox & David Patterson

Licensed under

Creative Commons Attribution-

NonCommercial-ShareAlike 3.0 Unported

What view should be rendered


23/25

What view should be rendered

for create action?

Idiom: redirectuser to a more useful page.e.g., list of movies, if create successfule.g., New Movie form, if unsuccessfulRedirect triggers a whole new HTTPrequestHow to inform userwhythey were redirected?Solution: flash[]quacks like a hash that

persists until end ofnextrequestflash[:notice] conventionally for informationflash[:warning] conventionally for errors


24/25

Flash & Session

session[]: like a hash that persists foreverreset_sessionnukes the whole thingsession.delete(:some_key), like a hashBy default, cookies store entire contents ofsession & flash

Alternative: store sessions in DB table (Google railssession use database table)Another alternative: store sessions in a NoSQLstorage system, like memcached


25/25

Truebut a bad idea!

False, because you cant put arbitrary

objects into a hashFalse, because session[] isnt really ahash, it just quacks like one

Trueknock yourself out!

*

Ben Bitdiddle says: You can put arbitraryobjects (not just simple ones like ints and

strings) into the session[]. What do youthink?

Documents

Handouts Slides Basic Rails