Arel Examples

example_1.rb

#--------------
# Basic Example
#--------------

require "./models"

name_variable = "Bill Smith"

# ActiveRecord
puts Customer.where(name: name_variable)

# Arel
puts Customer.where(Customer[:name].eq name_variable)

example_2.rb

#--------------------------
# A bit more useful example
#--------------------------

require "./models"

sales_var = 999

# ActiveRecord
# NOT GOOD (will raise)
# puts Customer.joins(:sales).where(price: sales_var)

# GOOD
puts Customer.joins(:sales).where("sales.price" => sales_var)

# Arel
puts Customer.joins(:sales).where(Sale[:price].eq sales_var)

example_3.rb

#------------------------
# SQL comparisons example
#------------------------

require "./models"

credits_var = 300

# ActiveRecord
puts Customer.where("credits > ?", credits_var)

# Arel
puts Customer.where(Customer[:credits].gt(credits_var))

# Comparison operators: gt, lt, gteq, lteq

example_4.rb

#----------------------
# OR conditions example
#----------------------

require "./models"

var1 = 800
var2 = 300

# ActiveRecord
puts Customer.where("credits > ? OR credits < ?", var1, var2)

# Arel
puts Customer.where(
  Customer[:credits].gt(var1).or(
    Customer[:credits].lt(var2)
  )
)

example_5.rb

#---------------------------
# Complex conditions example
#---------------------------

require "./models"

var1 = 800
var2 = "Mary Smith"
var3 = 500

# ActiveRecord
puts Customer.where("credits > ? OR (name = ? AND credits < ?)", var1, var2, var3)

# Arel
puts Customer.where(
  Customer[:credits].gt(var1).or(
    Customer[:name].eq(var2).and(
      Customer[:credits].lt(var3)
    )
  )
)

example_6.rb

#-------------
# LIKE example
#-------------

require "./models"

name_var = "Mary"

# ActiveRecord
puts Customer.where("name LIKE ?", "%#{name_var}%")

# Arel
puts Customer.where(Customer[:name].matches("%#{name_var}%"))

model.rb

require "active_record"
require "pg"

# AR connection
ActiveRecord::Base.establish_connection(
  adapter:  "postgresql",
  database: "lynda_test",
  username: "bruno",
  password: nil,
  host:     "localhost",
  port:     "5432",
)

# Columns:
#   id       :integer, primary_key
#   name     :string
#   credits  :integer
class Customer < ActiveRecord::Base
  has_many :sales

  def self.[](column)
    arel_table[column]
  end

  def to_s
    "id: #{id}, name: #{name}, credits: #{credits}"
  end
end

# Columns:
#   id           :integer, primary_key
#   customer_id  :integer
#   price        :integer
class Sale < ActiveRecord::Base
  belongs_to :customer

  def self.[](column)
    arel_table[column]
  end
end