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# frozen_string_literal: true
module Gitlab
module BackgroundMigration
# Background migration that updates the value of one or more
# columns using the value of other columns in the same table.
#
# - The {start_id, end_id} arguments are at the start so that it can be used
# with `queue_batched_background_migration`
# - Uses sub-batching so that we can keep each update's execution time at
# low 100s ms, while being able to update more records per 2 minutes
# that we allow background migration jobs to be scheduled one after the other
# - We skip the NULL checks as they may result in not using an index scan
# - The table that is migrated does _not_ need `id` as the primary key
# We use the provided primary_key column to perform the update.
class CopyColumnUsingBackgroundMigrationJob < BatchedMigrationJob
job_arguments :copy_from, :copy_to
operation_name :update_all
feature_category :database
def perform
assignment_clauses = build_assignment_clauses(copy_from, copy_to)
each_sub_batch do |relation|
relation.update_all(assignment_clauses)
end
end
private
def build_assignment_clauses(copy_from, copy_to)
copy_from = Array.wrap(copy_from)
copy_to = Array.wrap(copy_to)
unless copy_from.count == copy_to.count
raise ArgumentError, 'number of source and destination columns must match'
end
assignments = copy_from.zip(copy_to).map do |from_column, to_column|
from_column = connection.quote_column_name(from_column)
to_column = connection.quote_column_name(to_column)
"#{to_column} = #{from_column}"
end
assignments.join(', ')
end
end
end
end
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