where_preference.rb

class User < ActiveRecord::Base
  def self.my_where(key, value)
    # Normally with 2 arguments, you can easily do:
    where(key: value)
  end
  
  def self.where_preference(conditions)
    # But with a map and several k-v pairs, you'd have to do something like
    conditions.inject(self) do |scope, (k, v)|
      scope.where(k => v)
    end
    # But what is `subject` here so that this can be chainable with other Arel queries?
    # The reason I ned this is for an hstore query that looks like:
    # where("preferences @> hstore(:key,:value)", key: k, value: v)
  end
end