Add iteration_id column to lists

Also adds a foreign key constraint and cascades deletes when the
iteration is deleted

changelogs/unreleased/250479-iteration-lists-creation.yml

+---
+title: Add iteration_id column to lists
+merge_request: 48103
+author:
+type: added

db/migrate/20201119031515_add_iteration_id_to_lists.rb

+# frozen_string_literal: true
+
+class AddIterationIdToLists < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  def change
+    add_column :lists, :iteration_id, :bigint
+  end
+end

db/migrate/20201119053603_add_iteration_lists_foreign_key.rb

+# frozen_string_literal: true
+
+class AddIterationListsForeignKey < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  INDEX_NAME = 'index_lists_on_iteration_id'
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :lists, :iteration_id, name: INDEX_NAME
+    add_concurrent_foreign_key :lists, :sprints, column: :iteration_id, on_delete: :cascade
+  end
+
+  def down
+    remove_foreign_key_if_exists :lists, :sprints, column: :iteration_id
+    remove_concurrent_index_by_name :lists, INDEX_NAME
+  end
+end

db/schema_migrations/20201119031515

+6d2e6937c9e41975b1fd402bf2985796792a1e5f8e4f4f98bc76b65ff73c4e02
\ No newline at end of file

db/schema_migrations/20201119053603

+c7567489156bbc047cf9f7827f060ad507fd5d328179f2796566a7dc54806e3e
\ No newline at end of file

db/structure.sql

@@ -13593,7 +13593,8 @@ CREATE TABLE lists (
     milestone_id integer,
     max_issue_count integer DEFAULT 0 NOT NULL,
     max_issue_weight integer DEFAULT 0 NOT NULL,
-    limit_metric character varying(20)
+    limit_metric character varying(20),
+    iteration_id bigint
 );
 
 CREATE SEQUENCE lists_id_seq
@@ -21522,6 +21523,8 @@ CREATE UNIQUE INDEX index_list_user_preferences_on_user_id_and_list_id ON list_u
 
 CREATE UNIQUE INDEX index_lists_on_board_id_and_label_id ON lists USING btree (board_id, label_id);
 
+CREATE INDEX index_lists_on_iteration_id ON lists USING btree (iteration_id);
+
 CREATE INDEX index_lists_on_label_id ON lists USING btree (label_id);
 
 CREATE INDEX index_lists_on_list_type ON lists USING btree (list_type);
@@ -23174,6 +23177,9 @@ ALTER TABLE ONLY notes
 ALTER TABLE ONLY members
     ADD CONSTRAINT fk_2e88fb7ce9 FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;
 
+ALTER TABLE ONLY lists
+    ADD CONSTRAINT fk_30f2a831f4 FOREIGN KEY (iteration_id) REFERENCES sprints(id) ON DELETE CASCADE;
+
 ALTER TABLE ONLY approvals
     ADD CONSTRAINT fk_310d714958 FOREIGN KEY (merge_request_id) REFERENCES merge_requests(id) ON DELETE CASCADE;