Fix batched migrations using legacy job arguments

db/post_migrate/20210615234935_fix_batched_migrations_old_format_job_arguments.rb

+# frozen_string_literal: true
+
+class FixBatchedMigrationsOldFormatJobArguments < ActiveRecord::Migration[6.1]
+  class BatchedMigration < ActiveRecord::Base
+    self.table_name = 'batched_background_migrations'
+  end
+
+  def up
+    # rubocop:disable Style/WordArray
+    [
+      ['events', 'id', ['id', 'id_convert_to_bigint'], [['id'], ['id_convert_to_bigint']]],
+      ['push_event_payloads', 'event_id', ['event_id', 'event_id_convert_to_bigint'], [['event_id'], ['event_id_convert_to_bigint']]]
+    ].each do |table_name, column_name, legacy_job_arguments, current_job_arguments|
+      base_scope = BatchedMigration
+        .where(job_class_name: 'CopyColumnUsingBackgroundMigrationJob', table_name: table_name, column_name: column_name)
+      # rubocop:enable Style/WordArray
+
+      # rubocop:disable Rails/WhereEquals
+      base_scope
+        .where('job_arguments = ?', legacy_job_arguments.to_json)
+        .where('NOT EXISTS (?)', base_scope.select('1').where('job_arguments = ?', current_job_arguments.to_json))
+        .update_all(job_arguments: current_job_arguments)
+      # rubocop:enable Rails/WhereEquals
+    end
+  end
+
+  def down
+    # No-op, there is no way to know were the existing record migrated from
+    # legacy job arguments, or were using the current format from the start.
+    # There is no reason to go back anyway.
+  end
+end

db/schema_migrations/20210615234935

+205336e95a6e3c9fa8c56fa67e66ef3023ba8c6cd4e6f3599160b74b3fbfaa3c
\ No newline at end of file

spec/migrations/fix_batched_migrations_old_format_job_arguments_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require_migration!
+
+# rubocop:disable Style/WordArray
+RSpec.describe FixBatchedMigrationsOldFormatJobArguments do
+  let(:batched_background_migrations) { table(:batched_background_migrations) }
+
+  context 'when migrations with legacy job arguments exists' do
+    it 'updates job arguments to current format' do
+      legacy_events_migration = create_batched_migration('events', 'id', ['id', 'id_convert_to_bigint'])
+      legacy_push_event_payloads_migration = create_batched_migration('push_event_payloads', 'event_id', ['event_id', 'event_id_convert_to_bigint'])
+
+      migrate!
+
+      expect(legacy_events_migration.reload.job_arguments).to eq([['id'], ['id_convert_to_bigint']])
+      expect(legacy_push_event_payloads_migration.reload.job_arguments).to eq([['event_id'], ['event_id_convert_to_bigint']])
+    end
+  end
+
+  context 'when only migrations with current job arguments exists' do
+    it 'updates nothing' do
+      events_migration = create_batched_migration('events', 'id', [['id'], ['id_convert_to_bigint']])
+      push_event_payloads_migration = create_batched_migration('push_event_payloads', 'event_id', [['event_id'], ['event_id_convert_to_bigint']])
+
+      migrate!
+
+      expect(events_migration.reload.job_arguments).to eq([['id'], ['id_convert_to_bigint']])
+      expect(push_event_payloads_migration.reload.job_arguments).to eq([['event_id'], ['event_id_convert_to_bigint']])
+    end
+  end
+
+  context 'when migrations with both legacy and current job arguments exist' do
+    it 'updates nothing' do
+      legacy_events_migration = create_batched_migration('events', 'id', ['id', 'id_convert_to_bigint'])
+      events_migration = create_batched_migration('events', 'id', [['id'], ['id_convert_to_bigint']])
+      legacy_push_event_payloads_migration = create_batched_migration('push_event_payloads', 'event_id', ['event_id', 'event_id_convert_to_bigint'])
+      push_event_payloads_migration = create_batched_migration('push_event_payloads', 'event_id', [['event_id'], ['event_id_convert_to_bigint']])
+
+      migrate!
+
+      expect(legacy_events_migration.reload.job_arguments).to eq(['id', 'id_convert_to_bigint'])
+      expect(events_migration.reload.job_arguments).to eq([['id'], ['id_convert_to_bigint']])
+      expect(legacy_push_event_payloads_migration.reload.job_arguments).to eq(['event_id', 'event_id_convert_to_bigint'])
+      expect(push_event_payloads_migration.reload.job_arguments).to eq([['event_id'], ['event_id_convert_to_bigint']])
+    end
+  end
+
+  def create_batched_migration(table_name, column_name, job_arguments)
+    batched_background_migrations.create!(
+      max_value: 10,
+      batch_size: 10,
+      sub_batch_size: 10,
+      interval: 1,
+      job_class_name: 'CopyColumnUsingBackgroundMigrationJob',
+      table_name: table_name,
+      column_name: column_name,
+      job_arguments: job_arguments
+    )
+  end
+end
+# rubocop:enable Style/WordArray