两个关系的交集 [英] Intersection of two relations

问题描述

说我有两个关系持有记录在同一个模型，如：

Say I have two relations that hold records in the same model, such as:

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

我

如何才能找到这两个关系的交集，即只有在同时存在，这些公司？

How can I find the intersection of these two relations, i.e. only those companies that exist within both?

推荐答案

在默认情况下连接这些其中，一起创建并这是你想要的。

By default connecting those where together creates AND which is what you want.

因此​​，许多是：

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

@companies = Company.where_1.where_2

======修订==

====== UPDATED ======

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

所以，如果你是在第二种情况下，你需要做的像什么@apneadiving评论。

So if you are in case 2, you will need to do like what @apneadiving commented.

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

当然，这样做发出两个查询，并最有可能的查询比你需要更多的结果。

Of course, doing this sends out two queries and most likely queried more results than you needed.

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