Arel goodness (with CASE statement) in < v7

arel_patches.rb

# Remove this for Arel v7.0
module Arel
  module Nodes
    class Case < Arel::Nodes::Node
      include Arel::OrderPredications
      include Arel::Predications
      include Arel::AliasPredication

      attr_accessor :case, :conditions, :default

      def initialize expression = nil, default = nil
        @case = expression
        @conditions = []
        @default = default
      end

      def when condition, expression = nil
        @conditions << When.new(Nodes.build_quoted(condition), expression)
        self
      end

      def then expression
        @conditions.last.right = Nodes.build_quoted(expression)
        self
      end

      def else expression
        @default = Else.new Nodes.build_quoted(expression)
        self
      end

      def initialize_copy other
        super
        @case = @case.clone if @case
        @conditions = @conditions.map { |x| x.clone }
        @default = @default.clone if @default
      end

      def hash
        [@case, @conditions, @default].hash
      end

      def eql? other
        self.class == other.class &&
          self.case == other.case &&
          self.conditions == other.conditions &&
          self.default == other.default
      end
      alias :== :eql?
    end

    class When < Binary # :nodoc:
    end

    class Else < Unary # :nodoc:
    end
  end
end
module Arel
  module Visitors
    class DepthFirst < Arel::Visitors::Visitor
      alias :visit_Arel_Nodes_Else              :unary

      def visit_Arel_Nodes_Case o
        visit o.case
        visit o.conditions
        visit o.default
      end

      alias :visit_Arel_Nodes_When               :binary
    end
  end
end
module Arel
  module Predications
    def when right
      Nodes::Case.new(self).when quoted_node(right)
    end
  end
end

module Arel
  module Visitors
    class ToSql < Arel::Visitors::Reduce
      def visit_Arel_Nodes_Case o, collector
        collector << "CASE "
        if o.case
          visit o.case, collector
          collector << " "
        end
        o.conditions.each do |condition|
          visit condition, collector
          collector << " "
        end
        if o.default
          visit o.default, collector
          collector << " "
        end
        collector << "END"
      end

      def visit_Arel_Nodes_When o, collector
        collector << "WHEN "
        visit o.left, collector
        collector << " THEN "
        visit o.right, collector
      end

      def visit_Arel_Nodes_Else o, collector
        collector << "ELSE "
        visit o.expr, collector
      end
    end
  end
end