Load and merge application settings from YAML files.
At load time, settings are merged in two stages. First, all YAML data are recursively merged in reverse file order. Settings in succeeding files override all duplicate settings in preceding files. Second, the user selected settings—specified by key (e.g., environment key)—are recursively merged with the default settings.
This class can load multiple settings files, which provides a few benefits:
Confidential settings can be stored separately and securely from non-confidential settings; for example, in a public repository.
Settings for each application component or service (e.g., database, payment gateway, logger, CDN) can be stored in their respective files.
Shared or system-wide settings can be merged with application settings.
Settings File Examples
Absolute minimal settings
Above is the mandatory
default stanza, which must be present in at least one of the YAML settings files, even if it is empty. This isn't very useful, so lets add a couple of default settings.
default: setting_1: on setting_2: off
Here we have settings that specify the database name, user, host, and password file. There are three additional top-level stanzas:
test. These stanzas can be defined for any reason and have any name, but typically represent the runtime environment or mode of the application. Zero or more non-default top-level stanzas can be defined.
# database.yaml default: db: host: db.example.com user: dbusr pass: config/db-access development: db: name: myapp_dev production: db: name: myapp pass: /var/www/sites/myapp/db-access test: db: name: myapp_test
With these settings, the
default will always provide the database
user because it is not overridden in any other stanza. However, the database
name is not specified in
default because it is set in each environment. In
production, the database password file is unique—and secure of course—thus overrides
First things first!
Load database settings
production using the database settings above. The
production settings are merged into
settings = .('database.yaml', :production) settings.db.host # => "db.example.com" settings.db.user # => "dbusr" settings.db.name # => "myapp" settings.db.pass # => "/var/www/sites/myapp/db-access"
The settings are accessed using methods. The
db setting is actually a Hash and can also be accessed as such.
settings.db['host'] # => "db.example.com"
The difference is that method access raises an error if a setting is nonexistent.
settings.db.mia # KeyError: key not found: "mia" settings.db['mia'] # => nil
Method access is only available for string and symbol keys of Hash settings.
Load multiple settings files
It may be helpful to store settings for each application component separately. Or perhaps, settings are in a shared location. Here's how to initialize for such a situation:
settings = . '/etc/app-defaults.yml', # system wide '/etc/payment-gateway.yml', # system wide '/var/www/share/config/cdn.yml', # common for sites 'config/app.yml', # app specific 'config/database.yml', # app specific ENV['APP_MODE']
settings variable above is a compilation of four merges. First, config/database.yml will merge with and override config/app.yml; the result will merge with and override cdn.yml; and so on. Therefore, specify files with more generic settings first.
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Copyright © 2013-2017, Clint Pachl <[email protected]>
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