1 files changed, 38 insertions, 0 deletions
diff --git a/lib/gitlab/background_migration/batching_strategies/backfill_project_namespace_per_group_batching_strategy.rb b/lib/gitlab/background_migration/batching_strategies/backfill_project_namespace_per_group_batching_strategy.rb
new file mode 100644
index 00000000000..f352c527b54
--- /dev/null
+++ b/lib/gitlab/background_migration/batching_strategies/backfill_project_namespace_per_group_batching_strategy.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    module BatchingStrategies
+      # Batching class to use for back-filling project namespaces for a single group.
+      # Batches over the projects table and id column combination, scoped to a given group returning the MIN() and MAX()
+      # values for the next batch as an array.
+      #
+      # If no more batches exist in the table, returns nil.
+      class BackfillProjectNamespacePerGroupBatchingStrategy < PrimaryKeyBatchingStrategy
+        # Finds and returns the next batch in the table.
+        #
+        # table_name - The table to batch over
+        # column_name - The column to batch over
+        # batch_min_value - The minimum value which the next batch will start at
+        # batch_size - The size of the next batch
+        # job_arguments - The migration job arguments
+        def next_batch(table_name, column_name, batch_min_value:, batch_size:, job_arguments:)
+          next_batch_bounds = nil
+          model_class = ::Gitlab::BackgroundMigration::ProjectNamespaces::Models::Project
+          quoted_column_name = model_class.connection.quote_column_name(column_name)
+          projects_table = model_class.arel_table
+          hierarchy_cte_sql = Arel::Nodes::SqlLiteral.new(::Gitlab::BackgroundMigration::ProjectNamespaces::BackfillProjectNamespaces.hierarchy_cte(job_arguments.first))
+          relation = model_class.where(projects_table[:namespace_id].in(hierarchy_cte_sql)).where("#{quoted_column_name} >= ?", batch_min_value)
+
+          relation.each_batch(of: batch_size, column: column_name) do |batch| # rubocop:disable Lint/UnreachableLoop
+            next_batch_bounds = batch.pluck(Arel.sql("MIN(#{quoted_column_name}), MAX(#{quoted_column_name})")).first
+
+            break
+          end
+
+          next_batch_bounds
+        end
+      end
+    end
+  end
+end