Ruby-on-rails – ActiveRecord.find(array_of_ids), preserving order

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When you do Something.find(array_of_ids) in Rails, the order of the resulting array does not depend on the order of array_of_ids.

Is there any way to do the find and preserve the order?

ATM I manually sort the records based on order of IDs, but that is kind of lame.

UPD: if it's possible to specify the order using the :order param and some kind of SQL clause, then how?

Best Answer

Oddly, no one has suggested something like this:

index = Something.find(array_of_ids).group_by(&:id)
array_of_ids.map { |i| index[i].first }

As efficient as it gets besides letting SQL backend do it.

Edit: To improve on my own answer, you can also do it like this:

Something.find(array_of_ids).index_by(&:id).slice(*array_of_ids).values

#index_by and #slice are pretty handy additions in ActiveSupport for arrays and hashes respectively.

Related Solutions

Ruby-on-rails – Clean way to find ActiveRecord objects by id in the order specified

It's not that MySQL and other DBs sort things on their own, it's that they don't sort them. When you call Model.find([5, 2, 3]), the SQL generated is something like:

SELECT * FROM models WHERE models.id IN (5, 2, 3)

This doesn't specify an order, just the set of records you want returned. It turns out that generally MySQL will return the database rows in 'id' order, but there's no guarantee of this.

The only way to get the database to return records in a guaranteed order is to add an order clause. If your records will always be returned in a particular order, then you can add a sort column to the db and do Model.find([5, 2, 3], :order => 'sort_column'). If this isn't the case, you'll have to do the sorting in code:

ids = [5, 2, 3]
records = Model.find(ids)
sorted_records = ids.collect {|id| records.detect {|x| x.id == id}}

Rails/ActiveRecord: Return order with ActiveRecord#find(Array)

ActiveRecord is an interface to your database and returns the records to you in the same order that the database returns them. If you don't supply an 'order' parameter then the returned order is (effectively) random.

If your order is by id ascending or descending:

results = SomeModelName.find([1,2,3], :order => "id") # ascending order
results = SomeModelName.find([1,2,3], :order => "id desc") # descending order

If id order is not ascending or descending:

ids = [1, 3, 2]
r = SomeModelName.find(ids)
results = ids.map{|id| r.detect{|each| each.id == id}}

Best Answer

Related Solutions

Ruby-on-rails – Clean way to find ActiveRecord objects by id in the order specified

Rails/ActiveRecord: Return order with ActiveRecord#find(Array)

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