Add WikiAccessLevel migration from `NULL` to `20`

db/post_migrate/20180809195358_migrate_null_wiki_access_levels.rb

+# frozen_string_literal: true
+
+class MigrateNullWikiAccessLevels < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  class ProjectFeature < ActiveRecord::Base
+    include EachBatch
+
+    self.table_name = 'project_features'
+  end
+
+  def up
+    ProjectFeature.where(wiki_access_level: nil).each_batch do |relation|
+      relation.update_all(wiki_access_level: 20)
+    end
+  end
+
+  def down
+    # there is no way to rollback this change, there are no downsides in keeping migrated data.
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180808162000) do
+ActiveRecord::Schema.define(version: 20180809195358) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"

spec/migrations/migrate_null_wiki_access_levels_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20180809195358_migrate_null_wiki_access_levels.rb')
+
+describe MigrateNullWikiAccessLevels, :migration do
+  let(:namespaces) { table('namespaces') }
+  let(:projects) { table(:projects) }
+  let(:project_features) { table(:project_features) }
+  let(:migration) { described_class.new }
+
+  before do
+    namespace = namespaces.create(name: 'foo', path: 'foo')
+
+    projects.create!(id: 1, name: 'gitlab1', path: 'gitlab1', namespace_id: namespace.id)
+    projects.create!(id: 2, name: 'gitlab2', path: 'gitlab2', namespace_id: namespace.id)
+    projects.create!(id: 3, name: 'gitlab3', path: 'gitlab3', namespace_id: namespace.id)
+
+    project_features.create!(id: 1, project_id: 1, wiki_access_level: nil)
+    project_features.create!(id: 2, project_id: 2, wiki_access_level: 10)
+    project_features.create!(id: 3, project_id: 3, wiki_access_level: 20)
+  end
+
+  describe '#up' do
+    it 'migrates existing project_features with wiki_access_level NULL to 20' do
+      expect { migration.up }.to change { project_features.where(wiki_access_level: 20).count }.by(1)
+    end
+  end
+end