背景
正常的 rails 预加载集合是这样工作的:
Person.find(:all, :include=>:companies)
这会生成一些执行的 sql
LEFT OUTER JOIN companies ON people.company_id = companies.id
问题
但是,我需要一个自定义连接(如果我使用 find_by_sql
也会出现这种情况)所以我不能使用 vanilla :include => :companies
自定义 join/sql 将为我提供我需要的所有数据,但我如何告诉 activerecord 它属于关联的 Company
对象而不仅仅是一堆额外的行?
更新
我需要在联接中添加其他条件。像这样:
SELECT blah blah blah
LEFT OUTER JOIN companies ON people.company_id = companies.id AND people.magical_flag IS NULL
<Several other joins>
WHERE blahblahblah
最佳答案
可以不使用ActiveRecord添加连接条件吗?
例如,我有一个使用多个相关记录的非常复杂的查询,它通过组合条件和包含指令工作得很好
Contractors.find(
:all,
:include => {:council_areas => :suburbs},
:conditions => ["suburbs.postcode = ?", customer.postcode]
)
假设:
- 承包商有_many CouncilAreas
- CouncilAreas 有_many 郊区
此联接返回由 customer.postcode 标识的郊区的承包商。
生成的查询如下所示:
SELECT contractors.*, council_areas.*, suburbs.*
FROM `contractors`
LEFT OUTER JOIN `contractors_council_areas` ON `contractors_council_areas`.contractor_id = `contractors`.id
LEFT OUTER JOIN `council_areas` ON `council_areas`.id = `contractors_council_areas`.council_area_id
LEFT OUTER JOIN `council_areas_suburbs` ON `council_areas_suburbs`.council_area_id = `council_areas`.id
LEFT OUTER JOIN `suburbs` ON `suburbs`.id = `council_areas_suburbs`.suburb_id WHERE (suburbs.postcode = '5000')
(注意:为简洁起见,我编辑了列列表)。
关于sql - 如何使用自定义加入 rails 来加载对象?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/130268/