Compare dates in Rails with associated model without using .select

Question

Sorry if this has been posted elsewhere, not sure what to search for.

I have this query that is currently using .select, but there must be a better way to get the same result without using the dreaded .select? The mission is: find all shift cancellations that were created within 6 hours of when the shift was supposed to start:

ShiftCancellation.select{|c| c.created_at > c.shift.date_time - 6.hours}

ShiftCancellation belongs_to :shift and vice versa.

I'm on Postgres, so SQL-exclusive queries won't work.

Matt · Answer 1 · 2017-12-15T15:05:49.037

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You can join to the other table to allow all fields to be queried, but I'm not sure what the best way to get the date - 6hours is. I think DATE_SUB may be what you need:

ShiftCancellation.joins(:shift).where("shift_cancellations.created_at > DATE_SUB(shifts.date_time, INTERVAL 6 HOUR)"}

Bunch of examples here: https://stackoverflow.com/a/1888569/385532

edited Dec 15 '17 at 15:05

answered Dec 15 '17 at 14:53

Matt

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Ah sorry, forgot to mention I'm on Postgres, so DATE_SUB won't work. – mantralux Dec 15 '17 at 15:12
@mantralux check the examples in the link, there's a postgres alternative – Matt Dec 15 '17 at 16:08

score 0 · Answer 2 · answered Dec 15 '17 at 19:30

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Solved it.

ShiftCancellation.joins(:shift).where("shift_cancellations.created_at > (shifts.date_time - interval '6 hours')")

answered Dec 15 '17 at 19:30

mantralux

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Compare dates in Rails with associated model without using .select

2 Answers2