Implements migration scripts

gemfiles/rails4.gemfile

@@ -8,6 +8,8 @@ gem 'eventmachine' if ENV['EM']
 gem "activesupport", "< 5.0.0"
 gem "activemodel",   "< 5.0.0"
 
+gem 'generator_spec'
+
 group :development do
   gem 'pry'
   gem 'simplecov', :require => false

gemfiles/rails5.gemfile

@@ -8,6 +8,8 @@ gem 'eventmachine' if ENV['EM']
 gem "activesupport",     "< 6"
 gem "activemodel",       "< 6"
 
+gem 'generator_spec'
+
 group :development do
   gem 'pry'
   gem 'simplecov', :require => false

gemfiles/rails6.gemfile

@@ -8,8 +8,10 @@ gem 'eventmachine' if ENV['EM']
 gem "activesupport",     ">= 6.0.0"
 gem "activemodel",       ">= 6.0.0"
 
+gem 'generator_spec'
+
 group :development do
-  gem 'pry'
   gem 'awesome_print', :require => false
+  gem 'pry'
   gem 'simplecov', :require => false
 end

lib/no_brainer/error.rb

@@ -14,6 +14,7 @@ class LostLock                < RuntimeError; end
   class LockInvalidOp           < RuntimeError; end
   class LockUnavailable         < RuntimeError; end
   class InvalidPolymorphicType  < RuntimeError; end
+  class MigrationFailure        < RuntimeError; end
 
   class DocumentInvalid < RuntimeError
     attr_accessor :instance

lib/no_brainer/migration.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+module NoBrainer
+  #
+  # Parent class of all migration scripts.
+  # This class is used by the NoBrainer::Migrator class.
+  #
+  class Migration
+    class NoImplementedError < StandardError; end
+
+    def migrate!
+      up
+    rescue StandardError
+      raise unless respond_to?(:down)
+
+      begin
+        down
+        raise
+      rescue StandardError
+        raise
+      end
+    end
+
+    def rollback!
+      down if respond_to?(:down)
+    rescue StandardError
+      raise
+    end
+
+    def up
+      raise NoImplementedError
+    end
+  end
+end

lib/no_brainer/migrator.rb

@@ -0,0 +1,125 @@
+# frozen_string_literal: true
+
+module NoBrainer
+  #
+  # The Migrator class is used in order to execute a migration script and store
+  # the migration script "version" or timestap in a table allowing to run it
+  # only once.
+  # The mechanism is heavily inspired by the ActiveRecord one.
+  #
+  # It supports both migrate and rollback.
+  #
+  class Migrator
+    def self.migrations_table_name
+      'nobrainer_migration_versions'
+    end
+
+    def initialize(path)
+      @path = path
+      @version, snake_class_name = path.scan(%r{^.*/(\d+)_(.*)\.rb}).flatten
+
+      @name = snake_class_name ? snake_class_name.camelize : nil
+    end
+
+    def migrate
+      return if version_exists?
+
+      require @path
+
+      announce 'migrating'
+
+      time = Benchmark.measure do
+        migration_script = @name.constantize.new
+        migration_script.migrate!
+      end
+
+      announce 'migrated (%.4fs)' % time.real
+
+      create_version!
+    end
+
+    def rollback
+      return unless version_exists?
+
+      announce 'reverting'
+
+      require @path
+
+      time = Benchmark.measure do
+        migration_script = @name.constantize.new
+        migration_script.rollback!
+      end
+
+      announce 'reverted (%.4fs)' % time.real
+
+      remove_version!
+    end
+
+    private
+
+    # Stollen from the ActiveRecord gem
+    def announce(message)
+      text = "#{@version} #{@name}: #{message}"
+      length = [0, 75 - text.length].max
+      puts "== #{text} #{'=' * length}"
+    end
+
+    def check_if_version_exists?
+      NoBrainer.run do |r|
+        r.table(self.class.migrations_table_name).filter({ version: @version })
+      end.first.present?
+    end
+
+    def create_migrations_table_if_needed!
+      return if migrations_table_exists?
+
+      create_migrations_table!
+    end
+
+    def create_migrations_table!
+      result = NoBrainer.run do |r|
+        r.table_create(self.class.migrations_table_name)
+      end
+
+      return if result['tables_created'] == 1
+
+      raise NoBrainer::Error::MigrationFailure,
+            'Something prevented from creating the ' \
+            "'#{self.class.migrations_table_name}' table."
+    end
+
+    def create_version!
+      result = NoBrainer.run do |r|
+        r.table(self.class.migrations_table_name).insert({ version: @version })
+      end
+
+      return true if result['inserted'] == 1
+
+      raise NoBrainer::Error::MigrationFailure,
+            "Something prevented from inserting the version '#{@version}'"
+    end
+
+    def migrations_table_exists?
+      NoBrainer.run(&:table_list).include?(self.class.migrations_table_name)
+    end
+
+    def remove_version!
+      result = NoBrainer.run do |r|
+        r.table(self.class.migrations_table_name)
+         .filter({ version: @version })
+         .delete
+      end
+
+      return true if result['deleted'] == 1
+
+      raise NoBrainer::Error::MigrationFailure,
+            "Something prevented from deleting the version '#{@version}'"
+    end
+
+    def version_exists?
+      create_migrations_table_if_needed!
+
+      check_if_version_exists?
+    end
+  end
+end

lib/no_brainer/railtie/database.rake

@@ -1,3 +1,9 @@
+# frozen_string_literal: true
+
+def sorted_migration_script_pathes
+  Dir.glob(Rails.root.join('db', 'migrate', '*.rb')).sort
+end
+
 namespace :nobrainer do
   desc 'Drop the database'
   task :drop => :environment do
@@ -37,5 +43,22 @@ namespace :nobrainer do
   task :reset => [:drop, :sync_schema_quiet, :seed]
 
   task :create => [:sync_schema]
-  task :migrate => [:sync_schema]
+
+  desc 'Run migration scripts'
+  task :migrate => :environment do
+    NoBrainer.sync_schema
+
+    sorted_migration_script_pathes.each do |script|
+      migrator = NoBrainer::Migrator.new(script)
+      migrator.migrate
+    end
+  end
+
+  desc 'Rollback the last migration script'
+  task :rollback => :environment do
+    sorted_migration_script_pathes.reverse.each do |script|
+      migrator = NoBrainer::Migrator.new(script)
+      break if migrator.rollback
+    end
+  end
 end

lib/nobrainer.rb

@@ -16,7 +16,8 @@ module NoBrainer
   # Code that is loaded through the DSL of NoBrainer should not be eager loaded.
   autoload :Document, :IndexManager, :Loader, :Fork, :Geo, :SymbolDecoration
   eager_autoload :Config, :Connection, :ConnectionManager, :Error,
-                 :QueryRunner, :Criteria, :RQL, :Lock, :ReentrantLock, :Profiler, :System
+                 :QueryRunner, :Criteria, :RQL, :Lock, :ReentrantLock, :Profiler,
+                 :System, :Migrator, :Migration
 
   class << self
     delegate :connection, :disconnect, :to => 'NoBrainer::ConnectionManager'

lib/rails/generators/nobrainer/migration_generator.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require 'rails/generators/nobrainer/namespace_fix'
+require 'rails/generators/named_base'
+
+module NoBrainer
+  module Generators
+    #
+    # Generates a migration script prefixed with the date and time of
+    # its creation.
+    #
+    class MigrationGenerator < Rails::Generators::NamedBase
+      extend NoBrainer::Generators::NamespaceFix
+      source_root File.expand_path('../templates', __dir__)
+
+      desc 'Generates a new migration script in ./db/migrate/'
+
+      check_class_collision
+
+      def create_model_file
+        template 'migration.rb', File.join('db', 'migrate', timestamped_filename)
+      end
+
+      hook_for :test_framework
+
+      def timestamped_filename
+        "#{Time.current.strftime('%Y%m%d%H%M%S')}_#{file_name}.rb"
+      end
+    end
+  end
+end

lib/rails/generators/templates/migration.rb

@@ -0,0 +1,7 @@
+class <%= class_name %> < NoBrainer::Migration
+  def up
+  end
+
+  def down
+  end
+end