preferences

preferences adds support for easily creating custom preferences for models.

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Description

Preferences for models within an application, such as for users, is a pretty common idiom. Although the rule of thumb is to keep the number of preferences available to a minimum, sometimes it's necessary if you want users to be able to disable things like e-mail notifications.

Generally, basic preferences can be accomplished through simple designs, such as additional columns or a bit vector described and implemented by preference_fu. However, as you find the need for non-binary preferences and the number of preferences becomes unmanageable as individual columns in the database, the next step is often to create a separate “preferences” table. This is where the preferences plugin comes in.

preferences encapsulates this design by exposing preferences using simple attribute accessors on the model, hiding the fact that preferences are stored in a separate table and making it dead-simple to define and manage preferences.

Usage

Installation

preferences requires an additional database table to work. You can generate a migration for this table like so:

script/generate preferences

Then simply migrate your database:

rake db:migrate

Defining preferences

To define the preferences for a model, you can do so right within the model:

class User < ActiveRecord::Base
  preference :hot_salsa
  preference :dark_chocolate, :default => true
  preference :color, :string
  preference :favorite_number
  preference :language, :string, :default => 'English', :group_defaults => {:chat => 'Spanish'}
end

In the above model, 5 preferences have been defined:

For each preference, a data type and default value can be specified. If no data type is given, it's assumed to be a boolean value. If no default value is given, the default is assumed to be nil.

Accessing preferences

Once preferences have been defined for a model, they can be accessed either using the accessor methods that are generated for each preference or the generic methods that are not specific to a particular preference.

Accessors

There are several shortcut methods that are generated for each preference defined on a model. These reflect the same set of methods (attribute accessors) that are generated for a model's columns. Examples of these are shown below:

Query methods:

user.prefers_hot_salsa?         # => false
user.preferred_language?        # => true

Reader methods:

user.prefers_hot_salsa          # => false
user.preferred_language         # => "English"

Writer methods:

user.prefers_hot_salsa = false        # => false
user.preferred_language = 'English'   # => "English"

Generic methods

Each preference accessor is essentially a wrapper for the various generic methods shown below:

Query method:

user.prefers?(:hot_salsa)     # => false
user.preferred?(:language)    # => true

Reader method:

user.prefers(:hot_salsa)      # => false
user.preferred(:language)     # => "English"

Write method:

user.write_preference(:hot_salsa, false)      # => false
user.write_preference(:language, "English")   # => "English"

Accessing all preferences

To get the collection of all custom, stored preferences for a particular record, you can access the stored_preferences has_many association which is automatically generated:

user.stored_preferences

In addition to this, you can get a hash of all stored preferences and default preferences, by accessing the preferences helper:

user.preferences  # => {"language"=>"English", "color"=>nil}

This hash will contain the value for every preference that has been defined for the model, whether that's the default value or one that has been previously stored.

A short-hand alternative for preferences is also available:

user.prefs  # => {"language"=>"English", "color"=>nil}

Grouping preferences

In addition to defining generic preferences for the owning record, you can also group preferences by ActiveRecord objects or arbitrary names. This is best shown through an example:

user = User.find(:first)
car = Car.find(:first)

user.preferred_color = 'red', car
# user.write_preference(:color, 'red', car) # The generic way

This will create a color preference of “red” for the given car. In this way, you can have “color” preferences for different records.

To access the preference for a particular record, you can use the same accessor methods as before:

user.preferred_color(car)
# user.preferred(:color, car) # The generic way

In addition to grouping preferences for a particular record, you can also group preferences by name. For example,

user = User.find(:first)

user.preferred_color = 'red', :automobiles
user.preferred_color = 'tan', :clothing

user.preferred_color(:automobiles)  # => "red"
user.preferred_color(:clothing)     # => "tan"

user.preferences(:automobiles)      # => {"color"=>"red"}

Saving preferences

Note that preferences are not saved until the owning record is saved. Preferences are treated in a similar fashion to attributes. For example,

user = user.find(:first)
user.attributes = {:prefers_hot_salsa => false, :preferred_color => 'red'}
user.save!

Preferences are stored in a separate table called “preferences”.

Tracking changes

Similar to ActiveRecord attributes, unsaved changes to preferences can be tracked. For example,

user.preferred_language               # => "English"
user.preferred_language_changed?      # => false
user.preferred_language = 'Spanish'
user.preferred_language_changed?      # => true
user.preferred_language_was           # => "English"
user.preferred_language_change        # => ["English", "Spanish"]
user.reset_preferred_language!
user.preferred_language               # => "English"

Assigning the same value leaves the preference unchanged:

user.preferred_language               # => "English"
user.preferred_language = 'English'
user.preferred_language_changed?      # => false
user.preferred_language_change        # => nil

Testing

Before you can run any tests, the following gem must be installed:

To run against a specific version of Rails:

rake test RAILS_FRAMEWORK_ROOT=/path/to/rails

Dependencies