Rails Active Record查询只能联接，任何

Question

Student has_many :enrollments

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 })

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

Answer 1

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)

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).

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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.