Relation#each_batch doesn't respect limited datasets

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#329 2 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Stale
Tech stack
ruby, sql
Domain
database

Research direction

Start at the Relation#each_batch implementation and reproduce the issue with a limited relation such as users.limit(10) and a batch size of 10. Trace how the relation is used while batching, then ensure the existing limit remains effective; done means only the limited rows are processed.

Written by the indexing model from the issue text.

Description

bug

Describe the bug

When using Relation#each_batch, if you pass in a relation that already has a limit applied, Relation#each_batch will not respect it and process the batches as if the limit did not exist.

To Reproduce

users = ROM.env.relations[:users]
1000.times { create_user }
top_100 = users.limit(10)

i = 0
top_100.each_batch(size: 10) do |batch|
   i += 1
  raise 'This is unexpected...' if i > 10
end

Expected behavior

Relation#each_batch should respect the passed in limit, ideally by wrapping the input dataset in a subquery such that it will not be manipulated.

Your environment

  • Affects my production application: YES
  • Ruby version: 2.6.2
  • OS: Linux
Dominant language
Ruby
Stars
220
Forks
97
No merged PRs in 30d

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