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Settler can be used for defining application wide settings in Rails. Settings are loaded from a YAML file and stored in the database using ActiveRecord to allow users to update settings on the fly. The YAML configuration allows you to not only specify defaults, but setting value validations and typecasts as well!


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Settler can be used for defining application wide settings in Ruby. Settings are loaded from a YAML file and stored in the database using ActiveRecord to allow users to update settings on the fly. The YAML configuration allows you to not only specify defaults, but setting value validations and typecasts as well!


Settler v3 has not been released yet! You can find the latest v2 release code and docs here:


  • Ruby 1.9.2, 1.9.3, 2.0.0, 2.1.5, 2.2.2, 2.3.0 (tested)

Supported ORMs

  • Activerecord 3.1, 3.2, 4.0, 4.1, 4.2, 5.0 (tested)
  • In-memory store


Add the gem to your Gemfile:

gem 'settler'

Upgrading from v2

In settler v3, settler objects have been namespaced under the namespace Settler. Please update your sources accordingly:

Setting     => Settler::ORM::Activerecord::Setting
Typecaster  => Settler::Typecaster



  • A settler.yml file is needed to load the settings configuration. You can set its location as follows:

    Settler.source = '/path/to/my/settler.yml'

    By default, it will be set to config/settler.yml for Rails. The contents of this file are described in the section 'Configuration'.

  • A default YAML namespace can be set as follows:

    Settler.namespace = 'staging'


  • You must create the table used by the Settler::ORM::Activerecord::Setting model and install an initial configuration file. Simply run this command:

    rails g settler
  • This will create a migration and add a settler.yml configuration file in your config directory. Now just migrate the database:

    rake db:migrate
  • Next, you'll have to edit the settler.yml file, of which the details are described in the Configuration section.

  • You can manually set the configuration file source and default namespace as described above.


  • Settler.orm can be set to either :activerecord or :ruby. Default is :activerecord.
    • In :ruby mode, settings will not be persisted, but loaded in-memory instead.
    • In :activerecord mode, settings will be persisted using AR. However, settings will be loaded in :ruby mode when a database connection cannot be created or when the settings table has not been created (yet).
  • Settler.typecast_on_write should be set to true if you want values to be typecasted before they are written to the database.
  • Settler.password_secret can be used to set a custom secret for the password typecaster.


The initial version of settler.yml contains an example settings for specifying a google analytics key. A setting consists of at least a key and a value. Consider the following example:

  label: Google analytics key
  value: 'UA-xxxxxx-x'
  editable: true
  deletable: false
    presence: true

In this case, google_analytics_key is the key of the setting. Every nested property is either an attribute of the setting or a list of validations. Label, value, editable and deletable are attributes of the Settler::Setting model. If a setting with a given key does not exist, it is created with the attributes found. Therefore, you can consider these attributes as the default values for the setting. See the validations section for more info on validations.

Note that you can use ERB in the configuration file if you need to. For example:

  value: '<%= GOOGLE_ANALYTICS_KEY %>'

will evaluate the GOOGLE_ANALYTICS_KEY constant.

Access settings

  • Accessors will be created for every defined setting, returning a Setting instance:

    >> Settler.google_analytics_key
    Setting Load (0.7ms)   SELECT * FROM "settings" WHERE ("settings"."key" = 'google_analytics_key') LIMIT 1
    | id | key                  | label                | value      | editable | deletable |
    | 6  | google_analytics_key | Google analytics key | UA-xxxxx-x | true     | false     |
  • You can access a setting's value quickly by using the index operator:

    >> Settler[:google_analytics_key]
    Setting Load (0.7ms)   SELECT * FROM "settings" WHERE ("settings"."key" = 'google_analytics_key') LIMIT 1
    => "UA-xxxxx-x"
  • Activerecord only: some named scopes for finding setting are available that may be useful as well:

    • Settler::ORM::Activerecord::Setting.editable: returns all editable settings.
    • Settler::ORM::Activerecord::Setting.deletable: returns all deletable settings.
    • Settler::ORM::Activerecord::Setting.deleted: returns all deleted settings.


  • Setting values can be typecasted to several types. This can easily be done by adding a 'typecast' property to settler.yml. For example:

      label: A float that should be typecasted
      value: '0.25'
      typecast: float

    will ensure that the value returned by this setting will always be a float (0.25) instead if the string representation of a float.

  • The following typecasters are available by default:

    • integer
    • float
    • datetime
    • boolean
    • password

    Note: the boolean typecaster will yield true when the value is 1,t or true (case ignored), false otherwise.

  • It is possible to create and use your own typecaster instead of the built in typecasters. A custom type caster should look like this:

    class CustomTypecaster < Settler::Typecaster
      def typecast(value)
      # typecast and return value

When you require this class in your application, you can easily use your typecaster by specifying its class name in the settler configuration:

  label: An integer that should be custom typecasted
  value: 1
  typecast: CustomTypecaster



  • Validations are not stored in every setting, but are loaded on validation of a Setting instance. They apply to the value of the setting. The following validations can be created:
    • presence, true/false.
    • inclusion, followed by a YAML array (e.g. ['a','b','c']). Accepts a comma separated string as well.
    • format, followed by a YAML regex (e.g. !ruby/regexp "/^UA-.{6}-.$/i"). String can be given as well, which will be converted to a regex. Note that you will not be able to pass regex modifiers in that case, therefore the YAML regex syntax is recommended.

Changing / Destroying settings

Settings are represented by your ORM of choice. In the case of ActiveRecord, you can just update and destroy settings like you would update or destroy any AR model.


  • The key attribute is read only as it should never be changed through your application.

  • By default, settings will only be editable or deletable iff the corresponding attribute is set to true. This will be enforced before saving or destroying a record:

    >> Settler.google_analytics_key.destroy
    Setting Load (0.7ms)   SELECT \* FROM "settings" WHERE ("settings"."key" = 'google_analytics_key') LIMIT 1
    => false
  • Settings can be reset to the values defined in the configuration file by calling reset!:

    >> Settler.google_analytics_key.reset!
    => true

    Note that this will always work regardless of the editable attribute, so be careful when using this method!

  • The Settler::ORM::Activerecord::Setting model performs a soft delete when it is destroyed, meaning the record is not really destroyed, but just marked as deleted. The reason for doing this is because settings are reloaded from the configuration file when your application is (re)started, unless a setting is already available in the database. Therefore, it should know about all deleted settings, otherwise it would re-insert the deleted setting. If you want to enforce this behaviour, use Setting#delete instead.


  • The Ruby ORM just represents your YAML configuration as in-memory setting objects. You cannot edit or destroy these settings.

Advanced usage

  • When you define an inclusion validation on a setting, you can access these values for use in web forms by calling 'valid_values' on the setting:

    >> Settler.search_algorithm.valid_values
    Setting Load (0.7ms)   SELECT * FROM "settings" WHERE ("settings"."key" = 'search_algorithm') LIMIT 1
    => ["ferret", "sphinx"]

    NB: This method returns nil when valid values cannot be found.

  • Overriding setting attributes in the configuration is not as easy as it seems, since YAML doesn't support nested node merges. When overriding specific setting attributes, you should therefore do something like this:

    settings: &settings
      google_analytics_key: &google
      label: Google analytics key
      value: 'UA-xxxxxx-x'
      <<: *settings
        <<: *google
        label: Development Google analytics key
        value: 'UA-xxxxxx-1'
  • Report missing / raise missing

    • You can tell Settler to report missing attributes:

      Settler.report_missing = true

      This will output a warning to STDOUT and (if present) the Rails logger to notify you that a missing setting was requested.

    • It is also possible to raise an exception instead when requesting missing attributes:

      Settler.raise_missing = true

Note on Patches/Pull Requests

  • Fork the project.
  • Make your feature addition or bug fix.
  • Add tests for it. This is important so I don't break it in a future version unintentionally.
  • Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
  • Send me a pull request. Bonus points for topic branches.


Copyright (c) 2016 Reinier de Lange. See LICENSE for details.