how to each_cons in batches with active record - ruby-on-rails

Question

The following throws a LocalJumpError
records.find_each.each_cons(3)
Is there a built-in way to use each_cons in memory-friendly batches?
Edit:
Ideally the overlap would work across the batch limit. each_cons interates over overlapping groups, so records with ids (0, 1, 2), (1, 2, 3), (2, 3, 4) etc.
If the batch size is 1000 (which I think it is for Rails), it would be less than optimal to have the overlap limited within the batch group. For example the records with indexes (997, 998, 999) then next iteration to (1000, 1001, 1002) is undesirable.

Answer 1

Here's a custom method to accomplish it:
def batched_each_cons(batch_size:, each_cons:, model:)
end_of_previous = []
model.find_in_batches(batch_size: batch_size) do |batch|
rebuilt_batch = end_of_previous + batch
end_of_previous = batch[(-(each_cons-1))..-1]
rebuilt_batch.each_cons(each_cons) do |cons|
yield cons
end
end
end
batched_each_cons(batch_size: 5, each_cons: 3, model: User) do | users |
# puts users.map(&:name)
puts users.map(&:id).inspect
end
This gives:
User Load (0.7ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT $1 [["LIMIT", 5]]
[1, 2, 3]
[2, 3, 4]
[3, 4, 5]
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" > $1 ORDER BY "users"."id" ASC LIMIT $2 [["id", 5], ["LIMIT", 5]]
[4, 5, 6]
[5, 6, 7]
[6, 7, 8]
[7, 8, 9]
[8, 9, 10]
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" > $1 ORDER BY "users"."id" ASC LIMIT $2 [["id", 10], ["LIMIT", 5]]
[9, 10, 11]
[10, 11, 12]
[11, 12, 13]
[12, 13, 14]
[13, 14, 15]
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" > $1 ORDER BY "users"."id" ASC LIMIT $2 [["id", 15], ["LIMIT", 5]]
[14, 15, 16]
[15, 16, 17]
[16, 17, 18]
[17, 18, 19]
[18, 19, 20]
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" > $1 ORDER BY "users"."id" ASC LIMIT $2 [["id", 20], ["LIMIT", 5]]
(This is in my local console, normally you would not see 'User Load...', that is there to show the batching is working)

Answer 2

yeah, like this:
User.all.find_in_batches do |group|
group.each_cons(3) { |users| puts users.map(&:name) }
end