Add ProjectNamespace model and DB relationships

- Add ProjectNamespace model in Namespaces
- Add foreign key

Changelog: added

app/models/namespaces/project_namespace.rb

+# frozen_string_literal: true
+
+module Namespaces
+  class ProjectNamespace < Namespace
+    has_one :project, foreign_key: :project_namespace_id, inverse_of: :project_namespace
+  end
+end

app/models/project.rb

@@ -162,6 +162,7 @@ def topics
   belongs_to :creator, class_name: 'User'
   belongs_to :group, -> { where(type: 'Group') }, foreign_key: 'namespace_id'
   belongs_to :namespace
+  belongs_to :project_namespace, class_name: 'Namespaces::ProjectNamespace', foreign_key: 'project_namespace_id', inverse_of: :project
   alias_method :parent, :namespace
   alias_attribute :parent_id, :namespace_id
 

db/migrate/20210824055322_add_project_namespace_id_to_project.rb

+# frozen_string_literal: true
+
+class AddProjectNamespaceIdToProject < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def up
+    with_lock_retries do
+      # This is being added to Projects as a replacement for Namespace
+      # See https://gitlab.com/gitlab-org/gitlab/-/issues/337099
+      add_column :projects, :project_namespace_id, :bigint # rubocop: disable Migration/AddColumnsToWideTables
+    end
+  end
+
+  def down
+    with_lock_retries do
+      remove_column :projects, :project_namespace_id
+    end
+  end
+end

db/post_migrate/20210824102624_add_project_namespace_index_to_project.rb

+# frozen_string_literal: true
+
+class AddProjectNamespaceIndexToProject < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_projects_on_project_namespace_id'
+
+  def up
+    add_concurrent_index :projects, :project_namespace_id, name: INDEX_NAME, unique: true
+  end
+
+  def down
+    remove_concurrent_index_by_name :projects, INDEX_NAME
+  end
+end

db/post_migrate/20210824102750_add_project_namespace_foreign_key_to_project.rb

+# frozen_string_literal: true
+
+class AddProjectNamespaceForeignKeyToProject < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  TARGET_COLUMN = :project_namespace_id
+
+  def up
+    add_concurrent_foreign_key :projects, :namespaces, column: TARGET_COLUMN, on_delete: :cascade
+  end
+
+  def down
+    with_lock_retries do
+      remove_foreign_key_if_exists(:projects, column: TARGET_COLUMN)
+    end
+  end
+end

db/schema_migrations/20210824055322

+abd298ec9e6d9016c05032504d9ff0de7af9c6a031e0eacb041f29e59e82f289
\ No newline at end of file

db/schema_migrations/20210824102624

+f1fc9e062f5100db6a549fffa2fcd78d8eb6854cea388a6ac7addf4f6f232920
\ No newline at end of file

db/schema_migrations/20210824102750

+cc99eb2b40ee88d4d6df07253f599deb26be2fca7b941c5cecb2f8fb7ff3641d
\ No newline at end of file

db/structure.sql

@@ -18269,7 +18269,8 @@ CREATE TABLE projects (
     marked_for_deletion_at date,
     marked_for_deletion_by_user_id integer,
     autoclose_referenced_issues boolean,
-    suggestion_commit_message character varying(255)
+    suggestion_commit_message character varying(255),
+    project_namespace_id bigint
 );
 CREATE SEQUENCE projects_id_seq
@@ -26148,6 +26149,8 @@ CREATE INDEX index_projects_on_pending_delete ON projects USING btree (pending_d
 CREATE INDEX index_projects_on_pool_repository_id ON projects USING btree (pool_repository_id) WHERE (pool_repository_id IS NOT NULL);
+CREATE UNIQUE INDEX index_projects_on_project_namespace_id ON projects USING btree (project_namespace_id);
+
 CREATE INDEX index_projects_on_repository_storage ON projects USING btree (repository_storage);
 CREATE INDEX index_projects_on_runners_token ON projects USING btree (runners_token);
@@ -27662,6 +27665,9 @@ ALTER TABLE ONLY terraform_state_versions
 ALTER TABLE ONLY protected_branch_push_access_levels
     ADD CONSTRAINT fk_7111b68cdb FOREIGN KEY (group_id) REFERENCES namespaces(id) ON DELETE CASCADE;
+ALTER TABLE ONLY projects
+    ADD CONSTRAINT fk_71625606ac FOREIGN KEY (project_namespace_id) REFERENCES namespaces(id) ON DELETE CASCADE;
+
 ALTER TABLE ONLY integrations
     ADD CONSTRAINT fk_71cce407f9 FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE;

lib/gitlab/import_export/project/import_export.yml

@@ -128,6 +128,7 @@ excluded_attributes:
     - :name
     - :path
     - :namespace_id
+    - :project_namespace_id
     - :creator_id
     - :pool_repository_id
     - :import_url

spec/lib/gitlab/import_export/all_models.yml

@@ -370,6 +370,7 @@ project:
 - value_streams
 - group
 - namespace
+- project_namespace
 - management_clusters
 - boards
 - last_event

spec/models/namespaces/project_namespace_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Namespaces::ProjectNamespace, type: :model do
+  describe 'relationships' do
+    it { is_expected.to have_one(:project).with_foreign_key(:project_namespace_id).inverse_of(:project_namespace) }
+  end
+end

spec/models/project_spec.rb

@@ -16,6 +16,7 @@
   describe 'associations' do
     it { is_expected.to belong_to(:group) }
     it { is_expected.to belong_to(:namespace) }
+    it { is_expected.to belong_to(:project_namespace).class_name('Namespaces::ProjectNamespace').with_foreign_key('project_namespace_id').inverse_of(:project) }
     it { is_expected.to belong_to(:creator).class_name('User') }
     it { is_expected.to belong_to(:pool_repository) }
     it { is_expected.to have_many(:users) }

spec/requests/api/project_attributes.yml

@@ -32,6 +32,7 @@ itself: # project
     - pages_https_only
     - pending_delete
     - pool_repository_id
+    - project_namespace_id
     - pull_mirror_available_overridden
     - pull_mirror_branch_prefix
     - remote_mirror_available_overridden