1 files changed, 55 insertions, 0 deletions
diff --git a/railties/lib/rails/generators/rails/db/system/change/change_generator.rb b/railties/lib/rails/generators/rails/db/system/change/change_generator.rb
new file mode 100644
index 0000000000..63849eb18d
--- /dev/null
+++ b/railties/lib/rails/generators/rails/db/system/change/change_generator.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+require "rails/generators/base"
+
+module Rails
+  module Generators
+    module Db
+      module System
+        class ChangeGenerator < Base # :nodoc:
+          include Database
+          include AppName
+
+          class_option :to, required: true,
+            desc: "The database system to switch to."
+
+          def self.default_generator_root
+            path = File.expand_path(File.join(base_name, "app"), base_root)
+            path if File.exist?(path)
+          end
+
+          def initialize(*)
+            super
+
+            unless DATABASES.include?(options[:to])
+              raise Error, "Invalid value for --to option. Supported preconfigurations are: #{DATABASES.join(", ")}."
+            end
+
+            opt = options.dup
+            opt[:database] ||= opt[:to]
+            self.options = opt.freeze
+          end
+
+          def edit_database_config
+            template("config/databases/#{options[:database]}.yml", "config/database.yml")
+          end
+
+          def edit_gemfile
+            database_gem_name, _ = gem_for_database
+            gsub_file("Gemfile", all_database_gems_regex, database_gem_name)
+          end
+
+          private
+            def all_database_gems
+              DATABASES.map { |database| gem_for_database(database) }
+            end
+
+            def all_database_gems_regex
+              all_database_gem_names = all_database_gems.map(&:first)
+              /(\b#{all_database_gem_names.join('\b|\b')}\b)/
+            end
+        end
+      end
+    end
+  end
+end