ruby-on-rails - 两个关系的交集

Question

假设我有两个关系在同一模型中保存记录，例如:

@companies1 = Company.where(...)
@companies2 = Company.where(...)

如何找到这两种关系的交集，即仅存在于两者中的那些公司？

Answer 1

默认情况下，将这些 where 连接在一起会创建您想要的 AND。

很多是:

class Company < ActiveRecord::Base
  def self.where_1
    where(...)
  end
  def self.where_2
    where(...)
  end
end

@companies = Company.where_1.where_2

======已更新======

有两种情况:

# case 1: the fields selecting are different
Company.where(:id => [1, 2, 3, 4]) & Company.where(:other_field => true)
# a-rel supports &, |, +, -, but please notice case 2

# case 2
Company.where(:id => [1, 2, 3]) & Company.where(:id => [1, 2, 4, 5])

# the result would be the same as
Company.where(:id => [1, 2, 4, 5])
# because it is &-ing the :id key, instead of the content inside :id key

因此，如果您属于情况 2，则需要按照@apneadiving 的评论进行操作。

Company.where(...).all & Company.where(...).all

当然，这样做会发出两个查询，并且很可能查询到比您需要的更多的结果。