Rails Active Record查询只能联接，任何 [英] Rails Active Record Query joins only, any

问题描述

Student has_many :enrollments

通过此查询，我看到拥有 true 入学率的学生，还具有两者， true 和 false 报名：

With this query I see those students that have true enrollments, but also those that have both, true and false enrollments:

@students = Student.joins(:enrollments).where(enrollments: { is_active: false })

是否可以添加一些仅属性看到只有只名活跃学生的学生？

Is there some "only" attribute that I can add to see students that have only active enrollments?

推荐答案

一种简单的方法是找到学生无效的注册，然后将其明确排除在外。像这样的东西：

One way straightforward would be to find the students that inactive enrolments and then explicitly exclude them. Something like:

have_inactives = Enrollment.where(is_active: false).select(:student_id)
@students      = Student.joins(:enrollments).where.not(id: have_inactives)

joins（：enrollments）会过滤掉没有任何注册的学生条目以及 where.not （...）将排除所有未注册学生（使用子查询，因此所有作业仍将保留在其所属的数据库中）。

The joins(:enrollments) will filter out Student entries that don't have any enrolments and the where.not(...) will exclude all those students that have inactive enrolments (using a subquery so all the work will still be inside the database where it belongs).

顺便说一句，您可能想要修复注册的拼写，双l拼写错误可能最终使您或其他程序员发疯。

BTW, you might want to fix your spelling of "enrolment", the double-l misspelling will probably end up driving you or someone other programmer crazy.

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