Ensure active record can load without Railties

When I added the rake tasks for multiple databases I accidentally made
it so you couldn't use Active Record without Railties.

Since getting the database configuration depends on being able to load
Railties (there is no other way to read and parse the yaml file and load
it) I've decided that using multiple databases outside of Rails is a
no-op.

I've changed the code here to return if Rails isn't defined. Then I
changed the other tasks to use `ActiveRecord::Tasks::DatabaseTasks.env`
instead of `Rails.env`. The multi-db tasks can keep using `Rails.env`
because they'll only be generated if we're using Rails and not just
Active Record.

1 files changed, 2 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/tasks/database_tasks.rb b/activerecord/lib/active_record/tasks/database_tasks.rb
index 7285c15477..53e7e1e6d7 100644
--- a/activerecord/lib/active_record/tasks/database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/database_tasks.rb
@@ -142,6 +142,8 @@ module ActiveRecord
       end
 
       def for_each
+        return {} unless defined?(Rails)
+
         databases = Rails.application.config.load_database_yaml
         database_configs = ActiveRecord::DatabaseConfigurations.new(databases).configs_for(env_name: Rails.env)