ActiveRecord query returns object twice (2 instances of same object)

Question

Something is probably wrong with my query, not sure exactly what...

# this is the correct output
Plan.select { |p| p.plan_dates.select { |pd| pd.ddate.to_date >= cancel_from_this_date }.count > 0 }.map(&:id)
# => [54]

# this is the output where the object is returned twice
Plan.joins(:plan_dates).where("plan_dates.ddate >= ?", cancel_from_this_date.in_time_zone).pluck("id")
# => [54, 54]

abhinavmsra · Accepted Answer · 2015-07-27 16:47:49Z

2

It is quite natural.

Plan.joins(:plan_dates) returns a Plan object for all Plan with PlanDate.

Now, if multiple plan_dates have single Plan, you will get duplicate plans.

To resolve this, you need to use uniq as follows:

Plan.joins(:plan_dates).uniq.where("plan_dates.ddate >= ?", cancel_from_this_date.in_time_zone).pluck("id")

answered Jul 27, 2015 at 16:47

abhinavmsra

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5 Comments

abhinavmsra Over a year ago

your welcome. you can study more at guides.rubyonrails.org/active_record_querying.html

james Over a year ago

ugh i read that whole thing but i still am running into a zillion problems

abhinavmsra Over a year ago

can you mention them, if i can help?

james Over a year ago

YES good lord yes: 1) stackoverflow.com/questions/31658941/…, 2) stackoverflow.com/questions/31644628/…

JosephK Over a year ago

So, a Model-based query, filtered through another table's values with join, can return duplicates of the instances passed as the set to be filtered (the intention being to 'reduce' the set by returning only the matching values from the original-set). Absolutely crazy unexpected result from a step which should be subtractive - and quite difficult to track down. Thank you!!!

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