Relation#each_batch doesn't respect limited datasets

[ianks]

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

[flash-gordon]

Why do you think wrapping in a subquery is ideal here? In my opinion, taking current limit into consideration makes more sense.

[ianks]

That's good as well. The subquery is nice because you do not have to worry about twiddling around calculating the correct limits, and the user would not have to worry bout accidentally overriding the limit after the batch is yielded. However, it would add some complexity w/r/t remapping the current current clauses (i.e. making sure the exact same where clauses, etc) are added back to the yielded dataset. Either option is an improvement :)