ActiveRecord::Base

http://api.rubyonrails.org/classes/ActiveRecord/Base.html#M001343

  Company.find(:first, :conditions => [
   "id = :id AND name = :name AND division = :division AND created_at > :accounting_date",
   { :id => 3, :name => "37signals", :division => "First", :accounting_date => '2005-01-01' }
 ])
  Student.find(:all, :conditions => { :first_name => "Harvey", :status => 1 })
 Student.find(:all, :conditions => params[:student]);
 Student.find(:all, :conditions => { :grade => 9..12 })
 Student.find(:all, :conditions => { :grade => [9,11,12] })


 class Song < ActiveRecord::Base
   # Uses an integer of seconds to hold the length of the song
   def length=(minutes)
     write_attribute(:length, minutes.to_i * 60)
   end

   def length
     read_attribute(:length) / 60
   end
 end


 # Now 'Bob' exist and is an 'admin'
 User.find_or_create_by_name('Bob', :age => 40) { |u| u.admin = true }


 class User < ActiveRecord::Base
   serialize :preferences
 end
 user = User.create(:preferences => { "background" => "black", "display" => large })
 User.find(user.id).preferences # => { "background" => "black", "display" => large }


 class User < ActiveRecord::Base
   serialize :preferences, Hash
 end
 user = User.create(:preferences => %w( one two three ))
 User.find(user.id).preferences    # raises SerializationTypeMismatch


 User.create([{ :first_name => 'Jamie' }, { :first_name => 'Jeremy' }]) do |u|
   u.is_admin = false
 end


 # Delete multiple objects
 todos = [1,2,3]
 Todo.delete(todos)

 Person.find(1, 2, 6) # returns an array for objects with IDs in (1, 2, 6)
 Person.find([7, 17]) # returns an array for objects with IDs in (7, 17)

 Person.exists?(:name => "David")
 Person.exists?(['name LIKE ?', "%#{query}%"])


 Person.find(:all, :conditions => [ "category IN (?)", categories], :limit => 50)
 Person.find(:all, :conditions => { :friends => ["Bob", "Steve", "Fred"] }
 Person.find(:all, :offset => 10, :limit => 10)
 Person.find(:all, :include => [ :account, :friends ])
 Person.find(:all, :group => "category")

 Person.transaction do
   person = Person.find(1, :lock => true)
   person.visits += 1
   person.save!
 end

 Post.update_counters 5, :comment_count => -1, :action_count => 1

 { :name => "foo'bar", :group_id => 4 }
   # => "name='foo''bar' and group_id= 4"
 { :status => nil, :group_id => [1,2,3] }
   # => "status IS NULL and group_id IN (1,2,3)"
 { :age => 13..18 }
   # => "age BETWEEN 13 AND 18"
 { 'other_records.id' => 7 }
   # => "`other_records`.`id` = 7"