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| == Active Record ==
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|
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| === Create and Save ===
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|
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| <source lang="ruby">
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| article = Article.new # make an empty object
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| article.title = "My Title" # add attributes
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| article.author = "Herman"
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| article.save # save to database
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| </source>
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|
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| <source lang="ruby">
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| article.create(:title => "My Title", :author => "Herman") # make, set attributes, and save
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| </source>
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|
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| <source lang="ruby">
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| article.new_record? # new means not saved to database
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| </source>
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|
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| === Find ===
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| <source lang="ruby">
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| Article.find(3) # look for id = 3
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| Article.first # same as Article.find(:first), uses "LIMIT 1" in SQL, so may not be id = 1
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| Article.last # same as Article.find(:last)
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| Article.all # same as Article.find(:all)
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| Article.where(:title => 'RailsConf').first # chaining
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| Article.find_by_title('RailsConf') # dynamic finder
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| </source>
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|
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| === Update ===
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| <source lang="ruby">
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| article = Article.first
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| article.title = "Rails 3 is great"
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| article.published_at = Time.now
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| article.save
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| </source>
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| <source lang="ruby">
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| article = Article.first
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| article.update_attributes(:title => "RailsConf2010", :published_at => 1.day.ago) # saves too
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| </source>
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|
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| === Delete ===
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| <source lang="ruby">
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| Article.find(3).destroy # find, then destroy
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| Article.destroy(3) # same thing
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| Article.delete(3) # delete directly from database with no object callbacks
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| Article.delete_all("published_at < '2011-01-01'") # conditional
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| </source>
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|
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| === Validation and Errors ===
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| <source lang="ruby">
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| class Article< ActiveRecord::Base
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| validates :title, :presence => true
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| validates :body, :presence => true
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| end
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| </source>
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|
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| <source lang="ruby">
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| article = Article.new
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| article.errors.any? # false
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| article.save # returns false because of validation
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| article.errors.full_messages # ["Title can't be blank", "Body can't be blank"]
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| article.errors.on(:title) # "can't be blank"
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| article.valid? # false
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| </source>
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|
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| === Associations ===
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| ==== One-to-one ====
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| <source lang="ruby">
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| class User < ActiveRecord::Base
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| has_one :profile # assumes User.profile_id column
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| end # creates User.profile method
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| -------------------------------
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| class Profile < ActiveRecord::Base
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| belongs_to :user # assumes Profile.user_id column
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| end # creates Profile.user method
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| </source>
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|
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|
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| ==== One-to-many ====
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| <source lang="ruby">
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| class Message < ActiveRecord::Base
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| has_many :attachments # creates Message.attachments method
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| end
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| -------------------------------
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| class Attachment < ActiveRecord::Base
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| belongs_to :message # assumes Attachment.message_id column
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| end # creates Attachment.message method
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| </source>
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