sql - How can I order a Rails collection by the attributes of associated records? -


i have 3 models: teachers, students, , assignments

class teacher < activerecord::base   has_many :assignments   has_many :students, through: assignments, uniq: true end

for given teacher, retrieve list of unique students - simple enough, call:

teacher.students

however, order list of students based on has submitted assignments recently. specifically, student updated assignment appear first, , on.

i stuck on following code, not working:

teacher.students.group("assignments.student_id").order("max(assignments.updated_at) desc")

any suggestions?

it appears original query correct:

teacher.students.group("assignments.student_id").order("max(assignments.updated_at) desc")

i had thought wasn't working because had written bad rspec test failing because wasn't handling timestamps well. once used timecop handle timestamps properly, test passed.

sorry that.


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