Rails powered API - resource filters by URL params (ie /resources?user_id=12&state=active,finished)

filter_by_params_helper.rb

# (c) 2014 Lukas Dolezal (lukas@dolezalu.cz)
# MIT licence

# include in your base controller (ApplicationController)
# include FilterByParamsHelper
module FilterByParamsHelper

  # use in controller:
  # @resources = filter_by_params(@resources, params.slice(:user_id, :state))
  #
  # or
  # @resources = filter_by_params(@resources, filterable_params)
  # ...
  # protected
  # def filterable_params
  #   params.slice(:user_id, :state)
  # end
  #
  # call your URL:
  # /resources?user_id=12
  # or for select subset by multiple values:
  # /resources?user_id=12,34,56&state=valid,finished
  #
  # notice: values cannot contain commas "," as its used to determine set.
  def filter_by_params(resources, filter_params)
    filter =
    filter_params
    .select{|key, val| val.is_a? String}
    .map{|key, val|
      if val.include?(',')
        [key, val.split(',')]
      else
        [key, val]
      end
    }

    if filter.empty?
      resources
    else
      resources.where(Hash[filter])
    end
  end

end