Ruby on rails 轨道抛出'；列必须以'；无明显理由的例外

情况如下： 当在

psql

中运行或使用

ActiveRecord:：Base.connection.execute

SELECT SUM(loan_investments.amount) AS total_balance,
       COUNT(DISTINCT loan_investments.loan_id) AS number_of_loans,
       AVG(loan_investments.interest_rate) AS average_interest_rate,
       AVG(DATE_PART('month', loans.last_payment_date) - DATE_PART('month', NOW())) AS average_remaining_period 
FROM "loan_investments" 
INNER JOIN "loans" ON "loans"."id" = "loan_investments"."loan_id" 
WHERE "loan_investments"."user_id" = 8 
GROUP BY loan_investments.user_id;

下面是用于生成上述SQL的范围

 scope :performance_overview, -> {
     investments = joins(:loan)
     investments = investments.select("SUM(loan_investments.amount) AS total_balance,
                                  COUNT(DISTINCT loan_investments.loan_id) AS number_of_loans,
                                  AVG(loan_investments.interest_rate) AS average_interest_rate,
                                  AVG(DATE_PART('month', loans.last_payment_date) - DATE_PART('month', NOW())) AS average_remaining_period")
     investments.group('loan_investments.user_id')
  }

运行此作用域时，会引发以下异常：

错误：“loan_investments.id”列必须出现在GROUP BY子句中，或在聚合函数中使用

这是完全出乎意料的，因为loan_investments.id甚至不在任何地方使用，当在控制台中运行此sql时，它会产生正确的结果。我猜ActiveRecord想按

loan\u investments.id

进行分组，因为我们查询model

LoanInvestment

，但我不知道这是否正确

---

所以问题是为什么会出现此异常？

您在最后一行缺少一个作业

scope :performance_overview, -> {
 investments = joins(:loan)
 investments = investments.select("SUM(loan_investments.amount) AS total_balance,
                              COUNT(DISTINCT loan_investments.loan_id) AS number_of_loans,
                              AVG(loan_investments.interest_rate) AS average_interest_rate,
                              AVG(DATE_PART('month', loans.last_payment_date) - DATE_PART('month', NOW())) AS average_remaining_period")
 investments = investments.group('loan_investments.user_id')

---

}

您是否在调试日志中查看了实际生成的SQL语句？这个错误（很可能）不是来自Rails，而是来自Postgres，这意味着生成的SQL不是您所认为的。您可能希望通过添加到末尾来检查此作用域生成的SQL。提供的SQL是我从运行中收到的。要在给定作用域上创建SQL，我不太确定为什么我需要在最后一行添加一个赋值，因为investments.group（'loan\u investments.user\u id'））返回应返回的作用域关系，因为它始终是

invenstations

的一个附加项。但是，如果模型是

invenstation

并且范围在内部，则只需将元素与“.”连接在一起，而无需任何赋值。