Add pre migrations to allow more control of when data migrations can be run

Author: exosyphon-earthvectors

README.md

@@ -36,6 +36,31 @@ rake data:migrate
 
 This will run all pending data migrations and store migration history in `data_migrations` table. You're all set.
 
+If you need to generate migrations that can be run separately from data_migrations you can create Pre Migrations
+
+To create a pre data migration you need to run:
+```
+rails generate pre_data_migration migration_name
+```
+
+and this will create a `pre_migration_name.rb` file in `db/data_migrations` folder with a following content:
+```ruby
+class PreMigrationName < DataMigration
+  def up
+    # put your code here
+  end
+end
+```
+ 
+so all we need to do is to put some ruby code inside the `up` method.
+ 
+Finally, at the release time, you need to run 
+```
+rake data:migrate:pre
+```
+ 
+This will run all pending pre data migrations and store migration history in `data_migrations` table. You're all set.
+
 ## Rails Support
 
 Rails 4.0 and higher

lib/generators/pre_data_migration_generator.rb

@@ -0,0 +1,14 @@
+require 'rails/generators'
+require 'rails-data-migrations'
+
+class PreDataMigrationGenerator < Rails::Generators::NamedBase
+  source_root File.expand_path('../templates', __FILE__)
+
+  def create_migration_file
+    migration_file_name =
+      "#{RailsDataMigrations::Migrator.migrations_path}/#{Time.now.utc.strftime('%Y%m%d%H%M%S')}_pre_#{file_name}.rb"
+    copy_file 'data_migration_generator.rb', migration_file_name do |content|
+      content.sub(/ClassName/, "Pre#{file_name.camelize}")
+    end
+  end
+end

lib/rails_data_migrations/migrator.rb

@@ -53,9 +53,22 @@ def list_migrations
       def list_pending_migrations
         if rails_5_2?
           already_migrated = get_all_versions
-          list_migrations.reject { |m| already_migrated.include?(m.version) }
+          list_migrations
+            .reject { |m| already_migrated.include?(m.version) }
+            .reject { |m| m.filename.match(/\d{14}_pre_/) }
         else
-          open(migrations_path).pending_migrations
+          open(migrations_path).pending_migrations.reject { |m| m.filename.match(/\d{14}_pre_/) }
+        end
+      end
+
+      def list_pending_pre_migrations
+        if rails_5_2?
+          already_migrated = get_all_versions
+          list_migrations
+            .reject { |m| already_migrated.include?(m.version) }
+            .select { |m| m.filename.match(/\d{14}_pre_/) }
+        else
+          open(migrations_path).pending_migrations.select { |m| m.filename.match(/\d{14}_pre_/) }
         end
       end
 

lib/tasks/data_migrations.rake

@@ -34,6 +34,13 @@ namespace :data do
       apply_single_migration(:up, ENV['VERSION'])
     end
 
+    desc 'Apply pre data migrations'
+    task pre: :init_migration do
+      RailsDataMigrations::Migrator.list_pending_pre_migrations.sort_by(&:version).each do |m|
+        apply_single_migration(:up, m.version)
+      end
+    end
+
     desc 'Revert single data migration using VERSION'
     task down: :init_migration do
       apply_single_migration(:down, ENV['VERSION'])

spec/data_migrations_spec.rb

@@ -14,33 +14,62 @@
   context 'generator' do
     let(:migration_name) { 'test_migration' }
 
-    let(:file_name) { 'spec/db/data-migrations/20161031000000_test_migration.rb' }
+    context 'regular migration' do
+      let(:file_name) { 'spec/db/data-migrations/20161031000000_test_migration.rb' }
 
-    before(:each) do
-      allow(Time).to receive(:now).and_return(Time.utc(2016, 10, 31))
-      Rails::Generators.invoke('data_migration', [migration_name])
-    end
+      before(:each) do
+        allow(Time).to receive(:now).and_return(Time.utc(2016, 10, 31))
+        Rails::Generators.invoke('data_migration', [migration_name])
+      end
+
+      it 'creates non-empty migration file' do
+        expect(File.exist?(file_name)).to be_truthy
+        expect(File.size(file_name)).to be > 0
+      end
 
-    it 'creates non-empty migration file' do
-      expect(File.exist?(file_name)).to be_truthy
-      expect(File.size(file_name)).to be > 0
+      it 'creates valid migration class' do
+        # rubocop:disable Security/Eval
+        eval(File.open(file_name).read)
+        # rubocop:enable Security/Eval
+        klass = migration_name.classify.constantize
+        expect(klass.superclass).to eq(ActiveRecord::DataMigration)
+        expect(klass.instance_methods(false)).to eq([:up])
+      end
     end
 
-    it 'creates valid migration class' do
-      # rubocop:disable Security/Eval
-      eval(File.open(file_name).read)
-      # rubocop:enable Security/Eval
-      klass = migration_name.classify.constantize
-      expect(klass.superclass).to eq(ActiveRecord::DataMigration)
-      expect(klass.instance_methods(false)).to eq([:up])
+    context 'pre migration' do
+      let(:file_name) { 'spec/db/data-migrations/20190131000000_pre_test_migration.rb' }
+
+      before(:each) do
+        allow(Time).to receive(:now).and_return(Time.utc(2019, 1, 31))
+        Rails::Generators.invoke('pre_data_migration', [migration_name])
+      end
+
+      it 'creates non-empty pre migration file' do
+        expect(File.exist?(file_name)).to be_truthy
+        expect(File.size(file_name)).to be > 0
+      end
+
+      it 'creates valid pre migration class' do
+        # rubocop:disable Security/Eval
+        eval(File.open(file_name).read)
+        # rubocop:enable Security/Eval
+        klass = "pre_#{migration_name}".classify.constantize
+        expect(klass.superclass).to eq(ActiveRecord::DataMigration)
+        expect(klass.instance_methods(false)).to eq([:up])
+      end
     end
   end
 
   context 'migrator' do
     before(:each) do
-      allow(Time).to receive(:now).and_return(Time.utc(2016, 11, 1, 2, 3, 4))
+      allow(Time).to receive(:now).and_return(
+        Time.utc(2016, 11, 1, 2, 3, 4),
+        Time.utc(2019, 1, 1, 2, 3, 14)
+      )
 
       Rails::Generators.invoke('data_migration', ['test'])
+      Rails::Generators.invoke('pre_data_migration', ['test'])
     end
 
     def load_rake_rasks
@@ -54,7 +83,7 @@ def load_rake_rasks
     end
 
     it 'list migration file' do
-      expect(RailsDataMigrations::Migrator.list_migrations.size).to eq(1)
+      expect(RailsDataMigrations::Migrator.list_migrations.size).to eq(2)
     end
 
     it 'applies pending migrations only once' do
@@ -69,6 +98,17 @@ def load_rake_rasks
       end
     end
 
+    it 'applies pending pre migrations' do
+      expect(RailsDataMigrations::LogEntry.count).to eq(0)
+
+      load_rake_rasks
+
+      Rake::Task['data:migrate:pre'].execute
+
+      expect(RailsDataMigrations::Migrator.current_version).to eq(20190101020314)
+      expect(RailsDataMigrations::LogEntry.count).to eq(1)
+    end
+
     it 'requires VERSION to run a single migration' do
       ENV['VERSION'] = nil