ruby-on-rails - How i can write a query inside select in rails

Question

How can I write this query in Ruby on Rails? Query inside a select

SELECT id, 
       company_id, 
       (SELECT name 
        FROM   companies 
        WHERE  id = referred_to_id) AS name 
FROM   referrals 
WHERE  company_id = 21 

Answer 1

在 Rails 中，您真的不需要担心编写这样的 SQL。ActiveRecord处理所有简单 SQL 命令的创建。

只要您在模型中正确设置了关系，下面的代码将为您提供公司名称。

@referral = Referral.find(21)
@referral.company.name

请参阅有关 Active Record 关联的本教程

Answer 2

@referrals = Referral.select('id, company_id, (SELECT name FROM companies WHERE  id = referred_to_id) AS name').where(company_id: 21)

Answer 3

@referral = Referral.joins(:company).select([:id,:company_id]).where(id: 21).first

然后使用

@referral.id
@referral.company_id
@referral.company.name

Answer 4

使用 activerecord，您可以通过以下方式实现：

referral = Referral.find(21)
referral.company.name

但是，如果您真的只想面对这些属性，则可以使用：

record = Referral.where("referrals.company_id = 21").joins("left join companies on referrals.referred_to_id = companies.id").select("referrals.id , referrals.company_id, companies.name as name").first

现在您可以访问该特殊对象的属性：

record.id
record.company_id
record.name