Question

I have been using mysql in a new rails application, but now I wanted to give mongoDB a try so I installed mongo mapper and mongoid (to use mongo session). The installation seems to be fine because I can create mongo models. But for some reason rails is still trying to connect to mysql: Can't connect to local MySQL server.

This is horrible, because even if I wasn’t using mongo, rails shouldn’t be trying to connect to mysql for every request. It’s throwing that error even for non-existent urls.

What can I do to debug this? I guess I could try removing the mysql gem from the Gemfile and running bundle install. But I still don’t like the fact that it’s trying to connect even when I’m not using it. Shouldn’t it try to connect ‘lazily’ (ie: only on demand)?

development.rb:

Myapp::Application.configure do
  # Settings specified here will take precedence over those in config/application.rb

  # In the development environment your application's code is reloaded on
  # every request. This slows down response time but is perfect for development
  # since you don't have to restart the web server when you make code changes.
  config.cache_classes = false

  # Log error messages when you accidentally call methods on nil.
  config.whiny_nils = true

  # Show full error reports and disable caching
  config.consider_all_requests_local       = true
  config.action_controller.perform_caching = false

  # Don't care if the mailer can't send
  config.action_mailer.raise_delivery_errors = false

  # Print deprecation notices to the Rails logger
  config.active_support.deprecation = :log

  # Only use best-standards-support built into browsers
  config.action_dispatch.best_standards_support = :builtin

  # Raise exception on mass assignment protection for Active Record models
  config.active_record.mass_assignment_sanitizer = :strict

  # Log the query plan for queries taking more than this (works
  # with SQLite, MySQL, and PostgreSQL)
  config.active_record.auto_explain_threshold_in_seconds = 0.5

  # Do not compress assets
  config.assets.compress = false

  # Expands the lines which load the assets
  config.assets.debug = true
end

application.rb:

require File.expand_path('../boot', __FILE__)

require 'rails/all'

if defined?(Bundler)
  # If you precompile assets before deploying to production, use this line
  Bundler.require(*Rails.groups(:assets => %w(development test)))
  # If you want your assets lazily compiled in production, use this line
  # Bundler.require(:default, :assets, Rails.env)
end

module Myapp
  class Application < Rails::Application
# Settings in config/environments/* take precedence over those specified here.
# Application configuration should go into files in config/initializers
# -- all .rb files in that directory are automatically loaded.

# Custom directories with classes and modules you want to be autoloadable.
# config.autoload_paths += %W(#{config.root}/extras)

# Only load the plugins named here, in the order given (default is alphabetical).
# :all can be used as a placeholder for all plugins not explicitly named.
# config.plugins = [ :exception_notification, :ssl_requirement, :all ]

# Activate observers that should always be running.
# config.active_record.observers = :cacher, :garbage_collector, :forum_observer

# Set Time.zone default to the specified zone and make Active Record auto-convert to this zone.
# Run "rake -D time" for a list of tasks for finding time zone names. Default is UTC.
# config.time_zone = 'Central Time (US & Canada)'

# The default locale is :en and all translations from config/locales/*.rb,yml are auto loaded.
# config.i18n.load_path += Dir[Rails.root.join('my', 'locales', '*.{rb,yml}').to_s]
# config.i18n.default_locale = :de

# Configure the default encoding used in templates for Ruby 1.9.
config.encoding = "utf-8"

# Configure sensitive parameters which will be filtered from the log file.
config.filter_parameters += [:password]

# Use SQL instead of Active Record's schema dumper when creating the database.
# This is necessary if your schema can't be completely dumped by the schema dumper,
# like if you have constraints or database-specific column types
# config.active_record.schema_format = :sql

# Enforce whitelist mode for mass assignment.
# This will create an empty whitelist of attributes available for mass-assignment for all models
# in your app. As such, your models will need to explicitly whitelist or blacklist accessible
# parameters by using an attr_accessible or attr_protected declaration.
# config.active_record.whitelist_attributes = true

# Enable the asset pipeline
config.assets.enabled = true

# Version of your assets, change this if you want to expire all your assets
config.assets.version = '1.0'

config.generators do |g|
  g.orm :mongo_mapper
end
  end
end

Answer 1

When ActiveRecord is part of application, it tries to establish connection to database at startup. If it fails to connect, application won’t start.

The problem is here:

require 'rails/all'

This line includes all “usual” rails components, ActiveRecord among them. If you go to its definition, it should look like this (for rails 3.2):

require "rails"

%w(
  active_record
  action_controller
  action_mailer
  active_resource
  rails/test_unit
  sprockets
).each do |framework|
  begin
    require "#{framework}/railtie"
  rescue LoadError
  end
end

Take this code, remove active_record line and put it instead your rails/all line. Now, ActiveRecord isn’t included and your application will loudly fail when it sees ActiveRecord references in the code, like this:

config.active_record.mass_assignment_sanitizer = :strict

You need to remove these too. You don’t need to delete database.yml, but you probably should, since it has no meaning now.