h2. Configuring Rails Applications

This guide covers the configuration and initialization features available to Rails applications. By referring to this guide, you will be able to:

* Adjust the behavior of your Rails applications
* Add additional code to be run at application start time

endprologue.

h3. Locations for Initialization Code

Rails offers (at least) four good spots to place initialization code:

* application.rb
* Environment-specific Configuration Files
* Initializers
* After-Initializers

h3. Running Code Before Rails

To run some code before Rails itself is loaded, simply put it above the call to
+require 'rails/all'+ in your +application.rb+.

h3. Configuring Rails Components

In general, the work of configuring Rails means configuring the components of Rails, as well as configuring Rails itself. The +application.rb+ and environment-specific configuration files (such as +config/environments/production.rb+) allow you to specify the various settings that you want to pass down to all of the components. For example, the default Rails 3.0 +application.rb+ file includes this setting:

<ruby>
  config.filter_parameters += [:password]
</ruby>

This is a setting for Rails itself. If you want to pass settings to individual Rails components, you can do so via the same +config+ object:

<ruby>
  config.active_record.timestamped_migrations = false
</ruby>

Rails will use that particular setting to configure Active Record.

h4. Rails General Configuration

* +config.after_initialize+ takes a block which will be ran _after_ Rails has finished initializing. Useful for configuring values set up by other initializers:

<ruby>
  config.after_initialize do
    ActionView::Base.sanitized_allowed_tags.delete 'div'
  end
</ruby>

* +config.allow_concurrency+ should be set to +true+ to allow concurrent (threadsafe) action processing. Set to +false+ by default. You probably don't want to call this one directly, though, because a series of other adjustments need to be made for threadsafe mode to work properly. Can also be enabled with +threadsafe!+.

* +config.asset_host+ sets the host for the assets. Useful when CDNs are used for hosting assets rather than the application server itself. Shorter version of +config.action_controller.asset_host+.

* +config.asset_path+ takes a block which configures where assets can be found. Shorter version of +config.action_controller.asset_path+.

<ruby>
  config.asset_path = proc { |asset_path| "assets/#{asset_path}" }
</ruby>

* +config.autoload_once_paths+ accepts an array of paths from which Rails will automatically load from only once. All elements of this array must also be in +autoload_paths+.

* +config.autoload_paths+ accepts an array of additional paths to prepend to the load path. By default, all app, lib, vendor and mock paths are included in this list.

* +config.cache_classes+ controls whether or not application classes should be reloaded on each request. Defaults to _true_ in development, _false_ in test and production. Can also be enabled with +threadsafe!+.

* +config.cache_store+ configures which cache store to use for Rails caching. Options include +:memory_store+, +:file_store+, +:mem_cache_store+ or the name of your own custom class. Defaults to +:file_store+.

* +config.colorize_logging+ specifies whether or not to use ANSI color codes when logging information. Defaults to _true_.

* +config.consider_all_requests_local+ is generally set to +true+ during development and +false+ during production; if it is set to +true+, then any error will cause detailed debugging information to be dumped in the HTTP response. For finer-grained control, set this to +false+ and implement +local_request?+  in controllers to specify which requests should provide debugging information on errors.

* +config.controller_paths+ configures where Rails can find controllers for this application.

* +config.dependency_loading+ enables or disables dependency loading during the request cycle. Setting dependency_loading to _true_ will allow new classes to be loaded during a request and setting it to _false_ will disable this behavior. Can also be enabled with +threadsafe!+.

* +config.eager_load_paths+ accepts an array of paths from which Rails will eager load on boot if cache classes is enabled. All elements of this array must also be in +load_paths+.

* +config.encoding+ sets up the application-wide encoding. Defaults to UTF-8.

* +config.filter_parameters+ used for filtering out the parameters that you don't want shown in the logs, such as passwords or credit card numbers.

* +config.helper_paths+ configures where Rails can find helpers for this application.

* +config.log_level+ defines the verbosity of the Rails logger. In production mode, this defaults to +:info+. In development mode, it defaults to +:debug+.

* +config.log_path+ overrides the path to the log file to use. Defaults to +log/#{environment}.log+ (e.g. log/development.log or log/production.log).

* +config.logger+ accepts a logger conforming to the interface of Log4r or the default Ruby 1.8+ Logger class, which is then used to log information from Action Controller. Set to nil to disable logging.

* +config.middleware+ allows you to configure the application's middleware. This is covered in depth in the "Configuring Middleware" section below.

* +config.plugins+ accepts the list of plugins to load. If this is set to nil, all plugins will be loaded. If this is set to [], no plugins will be loaded. Otherwise, plugins will be loaded in the order specified.

* +config.preload_frameworks+ enables or disables preloading all frameworks at startup. Can also be enabled with +threadsafe!+. Defaults to +nil+, so is disabled.

* +config.reload_plugins+ enables or disables plugin reloading.

* +config.root+ configures the root path of the application.

* +config.secret_token+ used for specifying a key which allows sessions for the application to be verified against a known secure key to prevent tampering.

* +config.serve_static_assets+ configures Rails to serve static assets. Defaults to _true_, but in the production environment is turned off. The server software used to run the application should be used to serve the assets instead.

* +config.threadsafe!+ enables +allow_concurrency+, +cache_classes+, +dependency_loading+ and +preload_frameworks+ to make the application threadsafe.

WARNING: Threadsafe operation is incompatible with the normal workings of development mode Rails. In particular, automatic dependency loading and class reloading are automatically disabled when you call +config.threadsafe!+.

* +config.time_zone+ sets the default time zone for the application and enables time zone awareness for Active Record.

* +config.whiny_nils+ enables or disabled warnings when an methods of nil are invoked. Defaults to _false_.

h4. Configuring Generators

Rails 3 allows you to alter what generators are used with the +config.generators+ method. This method takes a block:

<ruby>
  config.generators do |g|
    g.orm :active_record
    g.test_framework :test_unit
  end
</ruby>

The full set of methods that can be used in this block are as follows:

* +force_plural+ allows pluralized model names. Defaults to _false_.
* +helper+ defines whether or not to generate helpers. Defaults to _true_
* +orm+ defines which orm to use. Defaults to _nil_, so will use Active Record by default.
* +integration_tool+ defines which integration tool to use. Defaults to _nil_
* +performance_tool+ defines which performance tool to use. Defaults to _nil_
* +resource_controller+ defines which generator to use for generating a controller when using +rails generate resource+. Defaults to +:controller+.
* +scaffold_controller+ different from +resource_controller+, defines which generator to use for generating a _scaffolded_ controller when using +rails generate scaffold+. Defaults to +:scaffold_controller+
* +stylesheets+ turns on the hook for stylesheets in generators. Used in Rails for when the +scaffold+ generator is ran, but this hook can be used in other generates as well.
* +test_framework+ defines which test framework to use. Defaults to _nil_, so will use Test::Unit by default.
* +template_engine+ defines which template engine to use, such as ERB or Haml. Defaults to +:erb+.

h4. Configuring Middleware

Every Rails application comes with a standard set of middleware which it uses in this order in the development environment:

* +ActionDispatch::Static+ is used to serve static assets. Disabled if +config.serve_static_assets+ is _true_.
* +Rack::Lock+ Will wrap the app in mutex so it can only be called by a single thread at a time. Only enabled if +config.action_controller.allow_concurrency+ is set to _false_, which it is by default.
* +ActiveSupport::Cache::Strategy::LocalCache+ Serves as a basic memory backed cache. This cache is not thread safe and is intended only for serving as a temporary memory cache for a single thread.
* +Rack::Runtime+ Sets an +X-Runtime+ header, containing the time (in seconds) taken to execute the request.
* +Rails::Rack::Logger+ Will notify the logs that the request has began. After request is complete, flushes all the logs.
* +ActionDispatch::ShowExceptions+ rescues any exception returned by the application and renders nice exception pages if the request is local or if +config.consider_all_requests_local+ is set to _true_. If +config.action_dispatch.show_exceptions+ is set to _false_, exceptions will be raised regardless.
* +ActionDispatch::RemoteIp+ checks for IP spoofing attacks. Configurable with the +config.action_dispatch.ip_spoofing_check+ and +config.action_dispatch.trusted_proxies+ settings.
* +Rack::Sendfile+ The Sendfile middleware intercepts responses whose body is being served from a file and replaces it with a server specific X-Sendfile header. Configurable with +config.action_dispatch_
* +ActionDispatch::Callbacks+ Runs the prepare callbacks before serving the request.
* +ActiveRecord::ConnectionAdapters::ConnectionManagement+ cleans active connections after each request, unless the +rack.test+ key in the request environment is set to _true_.
* +ActiveRecord::QueryCache+ caches all +SELECT+ queries generated in a request. If an +INSERT+ or +UPDATE+ takes place then the cache is cleaned.
* +ActionDispatch::Cookies+ sets cookies for the request.
* +ActionDispatch::Session::CookieStore+ is responsible for storing the session in cookies. An alternate middleware can be used for this by changing the +config.action_controller.session_store+ to an alternate value. Additionally, options passed to this can be configured by using +config.action_controller.session_options+.
* +ActionDispatch::Flash+ sets up the +flash+ keys. Only available if +config.action_controller.session_store+ is set to a value.
* +ActionDispatch::ParamsParser+ parses out parameters from the request into +params+
* +Rack::MethodOverride+ allows the method to be overridden if +params[:_method]+ is set. This is the middleware which supports the PUT and DELETE HTTP method types.
* +ActionDispatch::Head+ converts HEAD requests to GET requests and serves them as so.
* +ActionDispatch::BestStandardsSupport+ enables "best standards support" so that IE8 renders some elements correctly.

Besides these usual middleware, you can add your own by using the +config.middleware.use+ method:

<ruby>
  config.middleware.use Magical::Unicorns
</ruby>

This will put the +Magical::Unicorns+ middleware on the end of the stack. If you wish to put this middleware before another use +insert_before+:

<ruby>
  config.middleware.insert_before ActionDispatch::Head, Magical::Unicorns
</ruby>

There's also +insert_after+ which will insert a middleware _after_ another:

<ruby>
  config.middleware.insert_after ActionDispatch::Head, Magical::Unicorns
</ruby>

Middlewares can also be completely swapped out and replaced with others:

<ruby>
  config.middleware.swap ActionDispatch::BestStandardsSupport, Magical::Unicorns
</ruby>

h4. Configuring i18n

* +config.i18n.default_locale+ sets the default locale of an application used for i18n. Defaults to +:en+.

* +config.i18n.load_path+ sets the path Rails uses to look for locale files. Defaults to +config/locales/*.{yml,rb}+

h4. Configuring Active Record

<tt>config.active_record</tt> includes a variety of configuration options:

* +config.active_record.logger+ accepts a logger conforming to the interface of Log4r or the default Ruby 1.8.x Logger class, which is then passed on to any new database connections made. You can retrieve this logger by calling +logger+ on either an Active Record model class or an Active Record model instance. Set to nil to disable logging.

* +config.active_record.primary_key_prefix_type+ lets you adjust the naming for primary key columns. By default, Rails assumes that primary key columns are named +id+ (and this configuration option doesn't need to be set.) There are two other choices:
** +:table_name+ would make the primary key for the Customer class +customerid+
** +:table_name_with_underscore+ would make the primary key for the Customer class +customer_id+

* +config.active_record.table_name_prefix+ lets you set a global string to be prepended to table names. If you set this to +northwest_+, then the Customer class will look for +northwest_customers+ as its table. The default is an empty string.

* +config.active_record.table_name_suffix+ lets you set a global string to be appended to table names. If you set this to +_northwest+, then the Customer class will look for +customers_northwest+ as its table. The default is an empty string.

* +config.active_record.pluralize_table_names+ specifies whether Rails will look for singular or plural table names in the database. If set to +true+ (the default), then the Customer class will use the +customers+ table. If set to +false+, then the Customers class will use the +customer+ table.

* +config.active_record.default_timezone+ determines whether to use +Time.local+ (if set to +:local+) or +Time.utc+ (if set to +:utc+) when pulling dates and times from the database. The default is +:local+.

* +config.active_record.schema_format+ controls the format for dumping the database schema to a file. The options are +:ruby+ (the default) for a database-independent version that depends on migrations, or +:sql+ for a set of (potentially database-dependent) SQL statements.

* +config.active_record.timestamped_migrations+ controls whether migrations are numbered with serial integers or with timestamps. The default is +true+, to use timestamps, which are preferred if there are multiple developers working on the same application.

* +config.active_record.lock_optimistically+ controls whether ActiveRecord will use optimistic locking. By default this is +true+.

The MySQL adapter adds one additional configuration option:

* +ActiveRecord::ConnectionAdapters::MysqlAdapter.emulate_booleans+ controls whether ActiveRecord will consider all +tinyint(1)+ columns in a MySQL database to be booleans. By default this is +true+.

The schema dumper adds one additional configuration option:

* +ActiveRecord::SchemaDumper.ignore_tables+ accepts an array of tables that should _not_ be included in any generated schema file. This setting is ignored unless +config.active_record.schema_format == :ruby+.

h4. Configuring Action Controller

<tt>config.action_controller</tt> includes a number of configuration settings:

* +config.action_controller.asset_host+ sets the host for the assets. Useful when CDNs are used for hosting assets rather than the application server itself.

* +config.action_controller.asset_path+ takes a block which configures where assets can be found. Shorter version of +config.action_controller.asset_path+.

* +config.action_controller.page_cache_directory+ should be the document root for the web server and is set using <tt>Base.page_cache_directory = "/document/root"</tt>. For Rails, this directory has already been set to Rails.public_path (which is usually set to <tt>Rails.root + "/public"</tt>). Changing this setting can be useful to avoid naming conflicts with files in <tt>public/</tt>, but doing so will likely require configuring your web server to look in the new location for cached files.

* +config.action_controller.page_cache_extension+ configures the extension used for cached pages saved to +page_cache_directory+. Defaults to +.html+

* +config.action_controller.perform_caching+ configures whether the application should perform caching or not. Set to _false_ in development mode, _true_ in production.

* +config.action_controller.default_charset+ specifies the default character set for all renders. The default is "utf-8".

* +config.action_controller.logger+ accepts a logger conforming to the interface of Log4r or the default Ruby 1.8+ Logger class, which is then used to log information from Action Controller. Set to nil to disable logging.

* +config.action_controller.request_forgery_protection_token+ sets the token parameter name for RequestForgery. Calling +protect_from_forgery+ sets it to +:authenticity_token+ by default.

* +config.action_controller.allow_forgery_protection+ enables or disables CSRF protection. By default this is +false+ in test mode and +true+ in all other modes.

* +config.action_controller.relative_url_root+ can be used to tell Rails that you are deploying to a subdirectory. The default is +ENV['RAILS_RELATIVE_URL_ROOT']+.

The caching code adds two additional settings:

* +ActionController::Base.page_cache_directory+ sets the directory where Rails will create cached pages for your web server. The default is +Rails.public_path+ (which is usually set to +Rails.root + "/public"+).

* +ActionController::Base.page_cache_extension+ sets the extension to be used when generating pages for the cache (this is ignored if the incoming request already has an extension). The default is +.html+.

The Active Record session store can also be configured:

* +ActiveRecord::SessionStore::Session.table_name+ sets the name of the table used to store sessions. Defaults to +sessions+.

* +ActiveRecord::SessionStore::Session.primary_key+ sets the name of the ID column used in the sessions table. Defaults to +session_id+.

* +ActiveRecord::SessionStore::Session.data_column_name+ sets the name of the column which stores marshaled session data. Defaults to +data+.

h4. Configuring Action Dispatch

* +config.action_dispatch.session_store+ sets the name of the store for session data. The default is +:cookie_store+; other valid options include +:active_record_store+, +:mem_cache_store+ or the name of your own custom class.

h4. Configuring Action View

There are only a few configuration options for Action View, starting with four on +ActionView::Base+:

* +config.action_view.debug_rjs+ specifies whether RJS responses should be wrapped in a try/catch block that alert()s the caught exception (and then re-raises it). The default is +false+.

* +config.action_view.field_error_proc+ provides an HTML generator for displaying errors that come from Active Record. The default is <tt>Proc.new{ |html_tag, instance| %Q(%&lt;div class=&quot;field_with_errors&quot;&gt;#{html_tag}&lt;/div&gt;).html_safe }</tt>

* +config.action_view.default_form_builder+ tells Rails which form builder to use by default. The default is +ActionView::Helpers::FormBuilder+.

* +config.action_view.logger+ accepts a logger conforming to the interface of Log4r or the default Ruby 1.8+ Logger class, which is then used to log information from Action Mailer. Set to nil to disable logging.

* +config.action_view.erb_trim_mode+ gives the trim mode to be used by ERB. It defaults to +'-'+. See the "ERB documentation":http://www.ruby-doc.org/stdlib/libdoc/erb/rdoc/ for more information.

h4. Configuring Action Mailer

There are a number of settings available on +config.action_mailer+:

* +config.action_mailer.logger+ accepts a logger conforming to the interface of Log4r or the default Ruby 1.8+ Logger class, which is then used to log information from Action Mailer. Set to nil to disable logging.

* +config.action_mailer.smtp_settings+ allows detailed configuration for the +:smtp+ delivery method. It accepts a hash of options, which can include any of these options:
** +:address+ - Allows you to use a remote mail server. Just change it from its default "localhost" setting.
** +:port+ - On the off chance that your mail server doesn't run on port 25, you can change it.
** +:domain+ - If you need to specify a HELO domain, you can do it here.
** +:user_name+ - If your mail server requires authentication, set the username in this setting.
** +:password+ - If your mail server requires authentication, set the password in this setting.
** +:authentication+ - If your mail server requires authentication, you need to specify the authentication type here. This is a symbol and one of +:plain+, +:login+, +:cram_md5+.

* +config.action_mailer.sendmail_settings+ allows detailed configuration for the +sendmail+ delivery method. It accepts a hash of options, which can include any of these options:
** +:location+ - The location of the sendmail executable. Defaults to +/usr/sbin/sendmail+.
** +:arguments+ - The command line arguments. Defaults to +-i -t+.

* +config.action_mailer.raise_delivery_errors+ specifies whether to raise an error if email delivery cannot be completed. It defaults to +true+.

* +config.action_mailer.delivery_method+ defines the delivery method. The allowed values are +:smtp+ (default), +:sendmail+, and +:test+.

* +config.action_mailer.perform_deliveries+ specifies whether mail will actually be delivered. By default this is +true+; it can be convenient to set it to +false+ for testing.

* +config.action_mailer.default+ configures Action Mailer defaults. These default to:
<ruby>
  :mime_version => "1.0",
  :charset      => "UTF-8",
  :content_type => "text/plain",
  :parts_order  => [ "text/plain", "text/enriched", "text/html" ]
</ruby>

h4. Configuring Active Resource

There is a single configuration setting available on +config.active_resource+:

* +config.active_resource.logger+ accepts a logger conforming to the interface of Log4r or the default Ruby 1.8+ Logger class, which is then used to log information from Active Resource. Set to nil to disable logging.

h4. Configuring Active Support

There are a few configuration options available in Active Support:

* +config.active_support.bare+ enables or disables the loading of +active_support/all+ when booting Rails. Defaults to +nil+, which means +active_support/all+ is loaded.

* +config.active_support.escape_html_entities_in_json+ enables or disables the escaping of HTML entities in JSON serialization. Defaults to +true+.

* +config.active_support.use_standard_json_time_format+ enables or disables serializing dates to ISO 8601 format. Defaults to +false+.

* +ActiveSupport::BufferedLogger.silencer+ is set to +false+ to disable the ability to silence logging in a block. The default is +true+.

* +ActiveSupport::Cache::Store.logger+ specifies the logger to use within cache store operations.

* +ActiveSupport::Logger.silencer+ is set to +false+ to disable the ability to silence logging in a block. The default is +true+.


h3. Rails Environment Settings

Some parts of Rails can also be configured externally by supplying environment variables. The following environment variables are recognized by various parts of Rails:

* +ENV['RAILS_ENV']+ defines the Rails environment (production, development, test, and so on) that Rails will run under.

* +ENV['RAILS_RELATIVE_URL_ROOT']+ is used by the routing code to recognize URLs when you deploy your application to a subdirectory.

* +ENV["RAILS_ASSET_ID"]+ will override the default cache-busting timestamps that Rails generates for downloadable assets.

* +ENV["RAILS_CACHE_ID"]+ and +ENV["RAILS_APP_VERSION"]+ are used to generate expanded cache keys in Rails' caching code. This allows you to have multiple separate caches from the same application.

h3. Initialization events

Rails has 5 initialization events which can be hooked into (listed in order that they are ran):

* +before_configuration+: This is run as soon as the application constant inherits from +Rails::Application+. The +config+ calls are evaluated before this happens.
* +before_initialize+: This is run directly before the initialization process of the application occurs.
* +to_prepare+: Run after the initializers are ran for all Railties (including the application itself), but before eager loading and the middleware stack is built. 
* +before_eager_load+: This is run directly before eager loading occurs, which is the default behaviour for the _production_ environment and not for the +development+ enviroment.
* +after_initialize+: Run directly after the initialization of the application, but before the application initializers are run.


WARNING: Some parts of your application, notably observers and routing, are not yet set up at the point where the +after_initialize+ block is called.

h4. +Rails::Railtie#initializer+

Rails has several initializers that run on startup that are all defined by using the +initializer+ method from +Rails::Railtie+. Here's an example of the +initialize_whiny_nils+ initializer from Active Support:

<ruby>
  initializer "active_support.initialize_whiny_nils" do |app|
    require 'active_support/whiny_nil' if app.config.whiny_nils
  end
</ruby>


The +initializer+ method takes three arguments with the first being the name for the initializer and the second being an options hash (not shown here) and the third being a block. The +:before+ key in the options hash can be specified to specify which initializer this new initializer must run before, and the +:after+ key will specify which initializer to run this initializer _after_. 

Initializers defined using the +initializer+ method will be ran in the order they are defined in, with the exception of ones that use the +:before+ or +:after+ methods.

WARNING: You may put your initializer before or after any other initializer in the chain, as long as it is logical. Say you have 4 initializers called "one" through "four" (defined in that order) and you define "four" to go _before_ "four" but _after_ "three", that just isn't logical and Rails will not be able to determine your initializer order.

The block's argument of the +initialize+ is the instance of the application itself, and so we can access the configuration on it by using the +config+ method as this initializer does.

h4. Initializer files

After loading the framework and any gems and plugins in your application, Rails turns to loading initialization code from +config/initializers+. The files in this directory can be used to hold configuration settings that should be made after all of the frameworks and plugins are loaded.

NOTE: You can use subfolders to organize your initializers if you like, because Rails will look into the whole file hierarchy from the +initializers+ folder on down.

TIP: If you have any ordering dependency in your initializers, you can control the load order by naming. For example, +01_critical.rb+ will be loaded before +02_normal.rb+.

h3. Changelog

* November 26, 2010: Removed all config settings not available in Rails 3 (Ryan Bigg)
* August 13, 2009: Updated with config syntax and added general configuration options by "John Pignata"
* January 3, 2009: First reasonably complete draft by "Mike Gunderloy":credits.html#mgunderloy
* November 5, 2008: Rough outline by "Mike Gunderloy":credits.html#mgunderloy
