我定制了两个 ransack predicates，让查询日期范围更好用。 其实就是让结束日期取那一天的 59:59 分

代码如下：

# Custom ransack predicate to simplify query for date range
#
# See lib/ransack.rb in ransack gem
# See wiki https://github.com/activerecord-hackery/ransack/wiki/Custom-Predicates
Ransack.configure do |config|

  config.add_predicate 'beginning_of_day_gteq',
    arel_predicate: 'gteq',
    formatter: proc { |v| v.to_date.beginning_of_day },
    validator: proc { |v| v.present? },
    type: :string

  config.add_predicate 'end_of_day_lt',
    arel_predicate: 'lt',
    formatter: proc { |v| v.to_date.end_of_day },
    validator: proc { |v| v.present? },
    type: :string
end

全文见： http://lingceng.github.io/blog/2015/12/28/query-date-range-with-ransack/?from=ruby-china.org