Fix existing migrations for repository_storages_weighted column

For instances that upgraded to GitLab 13.1.x, it's likely that the
`application_settings.repository_storages_weighted` column did not
properly update. This happened because the schema for
`ApplicationSetting` may have been cached, so the newly-added column
wasn't visible to the model.

To ensure the column always has the right data, we make the
pre-deployment migration fill in the right data and flush the
cache. This essentially does the same thing as the post-deployment
migration, but it ensures that the application can properly run before
post-deployment migrations have completed.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/225588

changelogs/unreleased/jc-add-seed-to-repository-storages-weighted.yml

+---
+title: Fix existing repository_storages_weighted migrations
+merge_request: 35814
+author:
+type: fixed

db/migrate/20200508203901_add_repository_storages_weighted_to_application_settings.rb

@@ -3,11 +3,37 @@
 class AddRepositoryStoragesWeightedToApplicationSettings < ActiveRecord::Migration[6.0]
   DOWNTIME = false
 
+  class ApplicationSetting < ActiveRecord::Base
+    serialize :repository_storages
+    self.table_name = 'application_settings'
+  end
+
   def up
     add_column :application_settings, :repository_storages_weighted, :jsonb, default: {}, null: false
+
+    seed_repository_storages_weighted
   end
 
   def down
     remove_column :application_settings, :repository_storages_weighted
   end
+
+  private
+
+  def seed_repository_storages_weighted
+    # We need to flush the cache to ensure the newly-added column is loaded
+    ApplicationSetting.reset_column_information
+
+    # There should only be one row here due to
+    # 20200420162730_remove_additional_application_settings_rows.rb
+    ApplicationSetting.all.each do |settings|
+      storages = Gitlab.config.repositories.storages.keys.collect do |storage|
+        weight = settings.repository_storages.include?(storage) ? 100 : 0
+        [storage.to_sym, weight]
+      end
+
+      settings.repository_storages_weighted = Hash[storages]
+      settings.save!
+    end
+  end
 end

db/post_migrate/20200526000407_seed_repository_storages_weighted.rb

 # frozen_string_literal: true
 
 class SeedRepositoryStoragesWeighted < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
   class ApplicationSetting < ActiveRecord::Base
     serialize :repository_storages
     self.table_name = 'application_settings'
   end
 
   def up
+    # We need to flush the cache to ensure the newly-added column is loaded
+    ApplicationSetting.reset_column_information
+
+    # There should only be one row here due to
+    # 20200420162730_remove_additional_application_settings_rows.rb
     ApplicationSetting.all.each do |settings|
       storages = Gitlab.config.repositories.storages.keys.collect do |storage|
         weight = settings.repository_storages.include?(storage) ? 100 : 0
-        [storage, weight]
+        [storage.to_sym, weight]
       end
 
       settings.repository_storages_weighted = Hash[storages]

spec/migrations/add_repository_storages_weighted_to_application_settings_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'migrate', '20200508203901_add_repository_storages_weighted_to_application_settings.rb')
+
+RSpec.describe AddRepositoryStoragesWeightedToApplicationSettings, :migration do
+  let(:storages) { { "foo" => {}, "baz" => {} } }
+  let(:application_settings) do
+    table(:application_settings).tap do |klass|
+      klass.class_eval do
+        serialize :repository_storages
+      end
+    end
+  end
+
+  before do
+    allow(Gitlab.config.repositories).to receive(:storages).and_return(storages)
+  end
+
+  let(:application_setting) { application_settings.create! }
+  let(:repository_storages) { ["foo"] }
+
+  it 'populates repository_storages_weighted properly' do
+    application_setting.repository_storages = repository_storages
+    application_setting.save!
+
+    migrate!
+
+    expect(application_settings.find(application_setting.id).repository_storages_weighted).to eq({ "foo" => 100, "baz" => 0 })
+  end
+end