job-iteration can cause infinite loop when using multi-column cursor in different tables with the same attribute

[pedropb]

Reproduction steps:

• Run dev test on branch pb-bug-multi-cursor-different-tables
• See commit for more details: ec50219

Expected behaviour:

• Cursor should always move forward

Other notes

• Ran into this issue while working on Use Arel instead of String for AR Enumerator conditionals #456

[pedropb]

My initial investigation points to cursor_value not considering the table names when updating the cursor value.

These are the queries logged:

Product Load (0.9ms)  SELECT `products`.* FROM `products` INNER JOIN `comments` ON `comments`.`product_id` = `products`.`id` ORDER BY products.id,comments.id LIMIT 2
Product Load (1.0ms)  SELECT `products`.* FROM `products` INNER JOIN `comments` ON `comments`.`product_id` = `products`.`id` WHERE (products.id > '2' OR (products.id = '2' AND (comments.id > '2'))) ORDER BY products.id,comments.id LIMIT 2
Product Load (1.0ms)  SELECT `products`.* FROM `products` INNER JOIN `comments` ON `comments`.`product_id` = `products`.`id` WHERE (products.id > '3' OR (products.id = '3' AND (comments.id > '3'))) ORDER BY products.id,comments.id LIMIT 2

vs the expected positions:

# [ product.id, comment.id ]
[[1, 1], [2, 2], [2, 3], [3, 4], [3, 5], [3, 6]]

Once the cursor hits product.id = 3 it gets stuck, because the queries always returns [3, 4], [3, 5], and cursor_value does not use the table_name (iow: column.to_s.split(".").first) on @columns to update the value on the cursor:

job-iteration/lib/job-iteration/active_record_enumerator.rb

Lines 46 to 54 in 24c3053

	def cursor_value(record)
	positions = @columns.map do |column|
	attribute_name = column.to_s.split(".").last
	column_value(record, attribute_name)
	end
	return positions.first if positions.size == 1
	positions
	end