Rails 3: An improved Search agnostic model using Arel

realty_request_controller.rb

class RealtyRequestController < ApplicationController
  #... other actions ...
  def search
    @s = Search.new(RealtyRequest,params[:search]) do |s|
      s.contract_id :eq # value to search defaults to params[:search][:contract_id]
      s.price_max :lteq # same here
      s.price_min :gteq
      s.zone :matches, "%#{params[:search][:zone]}%" # here I look for '%param%'
      s.province :matches, "%#{params[:search][:province]}%"
      s.municipality :matches, "%#{params[:search][:municipality]}%"
      s.rooms :eq
      s.mq :eq
    end

    @realty_requests = @s.result # assing result
    @realty_requests.order(:created_at) # add order option

    # ... other rendering stuff ...
  end
end

search.rb

class Search
  attr_accessor :attributes

  def initialize(model, attrs = {})
    @attributes = {}
    @model = model
    @arel = model.arel_table

    model.columns.each do |field|
      pattr = field.name

      attrs = Hash[attrs.select {|k,v| !v.empty? }]
      searchable = !attrs[pattr].nil?

      @attributes[pattr.to_sym] = attrs[pattr] if searchable

      self.class.send(:define_method,field.name) do |cond, *value|
        attr = field.name.to_sym
        value = value.first || @attributes[attr] || nil
        @model = @model.where(@arel[attr].send(cond,value)) if searchable
      end
    end

    if block_given?
      yield self
    end
  end

  def result
    @model
  end
end