Remove constraints from sprints table

As part of the plan to make title an optional attribute for Iteration,
the non-null constraint is removed along with the uniqueness constraints
from the database while the application-level checks are preserved.

We are including a down migration to set any null titles to their
primary keys (ids) because we want to start accepting null titles
behind a feature flag in the same release.

Changelog: changed

db/migrate/20220304052335_remove_not_null_contraint_on_title_from_sprints.rb

+# frozen_string_literal: true
+
+class RemoveNotNullContraintOnTitleFromSprints < Gitlab::Database::Migration[1.0]
+  enable_lock_retries!
+
+  def up
+    change_column_null :sprints, :title, true
+  end
+
+  def down
+    execute <<~SQL
+      UPDATE sprints SET title = id WHERE title IS NULL
+    SQL
+
+    change_column_null :sprints, :title, false
+  end
+end

db/migrate/20220304061631_remove_unique_index_for_sprints_on_iterations_cadence_id_and_title.rb

+# frozen_string_literal: true
+
+class RemoveUniqueIndexForSprintsOnIterationsCadenceIdAndTitle < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_sprints_on_iterations_cadence_id_and_title'
+
+  def up
+    remove_concurrent_index_by_name :sprints, INDEX_NAME
+  end
+
+  def down
+    add_concurrent_index :sprints, [:iterations_cadence_id, :title], name: INDEX_NAME, unique: true
+  end
+end

db/migrate/20220304062107_remove_unique_index_for_sprints_on_project_id_and_title.rb

+# frozen_string_literal: true
+
+class RemoveUniqueIndexForSprintsOnProjectIdAndTitle < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_sprints_on_project_id_and_title'
+
+  def up
+    remove_concurrent_index_by_name :sprints, INDEX_NAME
+  end
+
+  def down
+    add_concurrent_index :sprints, [:project_id, :title], where: "project_id IS NOT NULL", name: INDEX_NAME, unique: true
+  end
+end

db/schema_migrations/20220304052335

+ba2bae8d9561eeab907ecf30664a593bdf93ab1041453f93794bf0be4464e92c
\ No newline at end of file

db/schema_migrations/20220304061631

+7394be90999876473cfe39c38e72f21c7bb36a5038300d6fe1354f15f3d77e21
\ No newline at end of file

db/schema_migrations/20220304062107

+a9aace14f847412c2af03cc6de61616a0f48d32d0fd24b25f6b1f85513c87139
\ No newline at end of file

db/structure.sql

@@ -20651,7 +20651,7 @@ CREATE TABLE sprints (
     group_id bigint,
     iid integer NOT NULL,
     cached_markdown_version integer,
-    title text NOT NULL,
+    title text,
     title_html text,
     description text,
     description_html text,
@@ -29065,12 +29065,8 @@ CREATE INDEX index_sprints_on_due_date ON sprints USING btree (due_date);
 
 CREATE INDEX index_sprints_on_group_id ON sprints USING btree (group_id);
 
-CREATE UNIQUE INDEX index_sprints_on_iterations_cadence_id_and_title ON sprints USING btree (iterations_cadence_id, title);
-
 CREATE UNIQUE INDEX index_sprints_on_project_id_and_iid ON sprints USING btree (project_id, iid);
 
-CREATE UNIQUE INDEX index_sprints_on_project_id_and_title ON sprints USING btree (project_id, title) WHERE (project_id IS NOT NULL);
-
 CREATE INDEX index_sprints_on_title ON sprints USING btree (title);
 
 CREATE INDEX index_sprints_on_title_trigram ON sprints USING gin (title gin_trgm_ops);

spec/migrations/remove_not_null_contraint_on_title_from_sprints_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+require_migration!
+
+RSpec.describe RemoveNotNullContraintOnTitleFromSprints, :migration, schema: 20220304052335 do
+  let(:migration) { described_class.new }
+  let(:namespaces) { table(:namespaces) }
+  let(:sprints) { table(:sprints) }
+  let(:iterations_cadences) { table(:iterations_cadences) }
+
+  let!(:group) { namespaces.create!(name: 'foo', path: 'foo') }
+  let!(:cadence) { iterations_cadences.create!(group_id: group.id, title: "cadence 1") }
+  let!(:iteration1) { sprints.create!(id: 1, title: 'a', group_id: group.id, iterations_cadence_id: cadence.id, start_date: Date.new(2021, 11, 1), due_date: Date.new(2021, 11, 5), iid: 1) }
+
+  describe '#down' do
+    it "removes null titles by setting them with ids" do
+      migration.up
+
+      iteration2 = sprints.create!(id: 2, title: nil, group_id: group.id, iterations_cadence_id: cadence.id, start_date: Date.new(2021, 12, 1), due_date: Date.new(2021, 12, 5), iid: 2)
+
+      migration.down
+
+      expect(iteration1.reload.title).to eq 'a'
+      expect(iteration2.reload.title).to eq '2'
+    end
+  end
+end