活动记录获取所有不匹配条件的实例答案

【问题标题】：Active record get all instance that do not match condition活动记录获取所有不匹配条件的实例
【发布时间】：2016-09-26 23:17:25
【问题描述】：

我有以下 AR 查询，它返回一组房间（在给定时间段内不可用的房间）：

rooms = Room.joins(:bookings).where("(bookings.start_date >= ? AND bookings.start_date <= ?) OR (bookings.end_date >= ? AND bookings.end_date <= ?) OR (bookings.start_date <= ? AND bookings.end_date >= ?)", from, to, from, to, from, to)

我想修改那个查询，让它返回所有其他房间；那是在请求的时间段内可用的那些。正确的结果如下：

all_rooms = Room.all
available_rooms = all_rooms - rooms

但我直接想在单个查询中获取可用房间。我已经添加了一个 .not 但它没有给我正确的结果：

rooms = Room.joins(:bookings).where.not("(bookings.start_date >= ? AND bookings.start_date <= ?) OR (bookings.end_date >= ? AND bookings.end_date <= ?) OR (bookings.start_date <= ? AND bookings.end_date >= ?)", from, to, from, to, from, to)

我应该如何修改查询？

【问题讨论】：

标签： ruby-on-rails activerecord querying

【解决方案1】：

假设：

A = (bookings.start_date >= ? AND bookings.start_date <= ?)
B = (bookings.end_date >= ? AND bookings.end_date <= ?) 
C = (bookings.start_date <= ? AND bookings.end_date >= ?)
first_logic  = A or B or C
second_logic = not(first_logic) = not(A or B or C) = not(A) and not(B) and not(C)

available_rooms 是second_logic 的条件，所以会是这样的：

available_rooms = Room.joins(:bookings)
                      .where.not("bookings.start_date >= ? AND bookings.start_date <= ?", from, to)
                      .where.not("bookings.end_date >= ? AND bookings.end_date <= ?", from, to)
                      .where.not("bookings.start_date <= ? AND bookings.end_date >= ?", from, to)

【讨论】：