1 files changed, 46 insertions, 0 deletions
diff --git a/app/services/todos/destroy/destroyed_issuable_service.rb b/app/services/todos/destroy/destroyed_issuable_service.rb
new file mode 100644
index 00000000000..db12965224b
--- /dev/null
+++ b/app/services/todos/destroy/destroyed_issuable_service.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+module Todos
+  module Destroy
+    class DestroyedIssuableService
+      BATCH_SIZE = 100
+
+      def initialize(target_id, target_type)
+        @target_id = target_id
+        @target_type = target_type
+      end
+
+      def execute
+        inner_query = Todo.select(:id).for_target(target_id).for_type(target_type).limit(BATCH_SIZE)
+
+        delete_query = <<~SQL
+        DELETE FROM "#{Todo.table_name}"
+        WHERE id IN (#{inner_query.to_sql})
+        RETURNING user_id
+        SQL
+
+        loop do
+          result = ActiveRecord::Base.connection.execute(delete_query)
+
+          break if result.cmd_tuples == 0
+
+          user_ids = result.map { |row| row['user_id'] }.uniq
+
+          invalidate_todos_cache_counts(user_ids)
+        end
+      end
+
+      private
+
+      attr_reader :target_id, :target_type
+
+      def invalidate_todos_cache_counts(user_ids)
+        user_ids.each do |id|
+          # Only build a user instance since we only need its ID for
+          # `User#invalidate_todos_cache_counts` to work.
+          User.new(id: id).invalidate_todos_cache_counts
+        end
+      end
+    end
+  end
+end