Add primary key to elasticsearch_indexed_projects

Add a new migration that promotes the unique index on
`elasticsearch_indexed_projects.project_id` to be the primary key of the
table.

changelogs/unreleased/270090-add-pk-to-elasticsearch-indexed-projects.yml

+---
+title: Add primary key to elasticsearch_indexed_projects
+merge_request: 48919
+author:
+type: changed

db/migrate/20201201161655_add_primary_key_to_elastic_search_indexed_projects.rb

+# frozen_string_literal: true
+
+class AddPrimaryKeyToElasticSearchIndexedProjects < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  UNIQUE_INDEX_NAME = 'index_elasticsearch_indexed_projects_on_project_id'
+  PRIMARY_KEY_NAME = 'elasticsearch_indexed_projects_pkey'
+
+  def up
+    execute(<<~SQL)
+      DELETE FROM elasticsearch_indexed_projects
+      WHERE project_id IS NULL
+    SQL
+
+    execute(<<~SQL)
+      ALTER TABLE elasticsearch_indexed_projects
+      ALTER COLUMN project_id SET NOT NULL,
+      ADD CONSTRAINT #{PRIMARY_KEY_NAME} PRIMARY KEY USING INDEX #{UNIQUE_INDEX_NAME}
+    SQL
+  end
+
+  def down
+    add_index :elasticsearch_indexed_projects, :project_id, unique: true, name: UNIQUE_INDEX_NAME # rubocop:disable Migration/AddIndex
+
+    execute(<<~SQL)
+      ALTER TABLE elasticsearch_indexed_projects
+      DROP CONSTRAINT #{PRIMARY_KEY_NAME},
+      ALTER COLUMN project_id DROP NOT NULL
+    SQL
+  end
+end

db/schema_migrations/20201201161655

+d9ad12dce02d6823536f3206e9c90a0da82c08089c3ce252e8ef28a59589e747
\ No newline at end of file

db/structure.sql

@@ -11935,7 +11935,7 @@ CREATE TABLE elasticsearch_indexed_namespaces (
 CREATE TABLE elasticsearch_indexed_projects (
     created_at timestamp with time zone NOT NULL,
     updated_at timestamp with time zone NOT NULL,
-    project_id integer
+    project_id integer NOT NULL
 );
 
 CREATE TABLE emails (
@@ -19253,6 +19253,9 @@ ALTER TABLE ONLY draft_notes
 ALTER TABLE ONLY elastic_reindexing_tasks
     ADD CONSTRAINT elastic_reindexing_tasks_pkey PRIMARY KEY (id);
 
+ALTER TABLE ONLY elasticsearch_indexed_projects
+    ADD CONSTRAINT elasticsearch_indexed_projects_pkey PRIMARY KEY (project_id);
+
 ALTER TABLE ONLY emails
     ADD CONSTRAINT emails_pkey PRIMARY KEY (id);
 
@@ -21054,8 +21057,6 @@ CREATE INDEX index_elasticsearch_indexed_namespaces_on_created_at ON elasticsear
 
 CREATE UNIQUE INDEX index_elasticsearch_indexed_namespaces_on_namespace_id ON elasticsearch_indexed_namespaces USING btree (namespace_id);
 
-CREATE UNIQUE INDEX index_elasticsearch_indexed_projects_on_project_id ON elasticsearch_indexed_projects USING btree (project_id);
-
 CREATE UNIQUE INDEX index_emails_on_confirmation_token ON emails USING btree (confirmation_token);
 
 CREATE UNIQUE INDEX index_emails_on_email ON emails USING btree (email);