Increment all attributes in a relation with two queries using ActiveRecord increment_counter and pluck methods

product.rb

class Product < ActiveRecord::Base
  
  # we could use the below version to acheive
  # the desired result in a single statement
  # with raw sql, however this solution
  # wouldn't be database agnostic and I think
  # most developers would prefer the ruby
  # version as two queries is still very
  # fast.
  #
  #  def self.increment_positions
  #    connection.execute("UPDATE products SET position = position + 1")
  #  end
  #
  # Additionally, this will update all rows
  # in the products table and connot be scoped.
  # The below version can.
  
  def self.increment_positions
    increment_counter :position, pluck(:id)
  end
  
end

product_spec.rb

describe ".increment_positions" do
  it 'increments all positions in a relation' do
    a, b = create(:product, position: 1), create(:product, position: 2)
    Product.increment_positions
    a.reload.position.must_equal 2
    b.reload.position.must_equal 3
  end

  it 'does not increment positions outside a relation' do
    a, b = create(:product, position: 1), create(:product, position: 2)
    Product.where.not(position: 1).increment_positions
    a.reload.position.must_equal 1
    b.reload.position.must_equal 3
  end
end