Module: Cms::Behaviors::DynamicAttributes

Defined in:

lib/cms/behaviors/dynamic_attributes.rb

Overview

The DynamicAttributes behavior allows a model to store values for any attributes. A model that uses DynamicAttributes should have corresponding “_attributes” table where it stores the values for the dynamic attributes. This is based on the Flex Attributes Rails Plugin.

class User < ActiveRecord::Base
  has_dynamic_attributes
end
eric = User.find_by_login 'eric'
puts "My AOL instant message name is: #{eric.aim}"
eric.phone = '555-123-4567'
eric.save

The above example should work even though “aim” and “phone” are not attributes on the User model.

The following options are available on for has_dynamic_attributes to modify the behavior. Reasonable defaults are provided:

class_name

The class for the related model. This defaults to the model name prepended to “Attribute”. So for a “User” model the class name would be “UserAttribute”. The class can actually exist (in that case the model file will be loaded through Rails dependency system) or if it does not exist a basic model will be dynamically defined for you. This allows you to implement custom methods on the related class by simply defining the class manually.

table_name

The table for the related model. This defaults to the attribute model’s table name.

relationship_name

This is the name of the actual has_many relationship. Most of the type this relationship will only be used indirectly but it is there if the user wants more raw access. This defaults to the class name underscored then pluralized finally turned into a symbol.

foreign_key

The key in the attribute table to relate back to the model. This defaults to the model name underscored prepended to “_id”

name_field

The field which stores the name of the attribute in the related object

value_field

The field that stores the value in the related object

fields

A list of fields that are valid dynamic attributes. By default this is “nil” which means that all field are valid. Use this option if you want some fields to go to one dynamic attribute model while other fields will go to another. As an alternative you can override the #dynamic_attributes method which will return a list of all valid dynamic attributes. This is useful if you want to read the list of attributes from another source to keep your code DRY. This method is given a single argument which is the class for the related model. The following provide an example:

class User < ActiveRecord::Base
  has_dynamic_attributes :class_name => 'UserContactInfo'
  has_dynamic_attributes :class_name => 'Preferences'

  def dynamic_attributes(model)
    case model
      when UserContactInfo
        %w(email phone aim yahoo msn)
      when Preference
        %w(project_search project_order user_search user_order)
      else Array.new
    end
  end
end

eric = User.find_by_login 'eric'
eric.email = 'eric@example.com' # Will save to UserContactInfo model
eric.project_order = 'name'     # Will save to Preference
eric.save # Carries out save so now values are in database

Note the else clause in our case statement. Since an empty array is returned for all other models (perhaps added later) then we can be certain that only the above dynamic attributes are allowed.

If both a :fields option and #dynamic_attributes method is defined the :fields option take precidence. This allows you to easily define the field list inline for one model while implementing #dynamic_attributes for another model and not having #dynamic_attributes need to determine what model it is answering for. In both cases the list of dynamic attributes can be a list of string or symbols

A final alternative to :fields and #dynamic_attributes is the #is_dynamic_attribute? method. This method is given two arguments. The first is the attribute being retrieved/saved the second is the Model we are testing for. If you override this method then the #dynamic_attributes method or the :fields option will have no affect. Use of this method is ideal when you want to retrict the attributes but do so in a algorithmic way. The following is an example:

class User < ActiveRecord::Base
  has_dynamic_attributes :class_name => 'UserContactInfo'
  has_dynamic_attributes :class_name => 'Preferences'

  def is_dynamic_attribute?(attr, model)
    case attr.to_s
      when /^contact_/ then true
      when /^preference_/ then true
      else
        false
    end
  end
end

eric = User.find_by_login 'eric'
eric.contact_phone = '555-123-4567'
eric.contact_email = 'eric@example.com'
eric.preference_project_order = 'name'
eric.some_attribute = 'blah'  # If some_attribute is not defined on
                              # the model then method not found is thrown

Defined Under Namespace

Modules: InstanceMethods, MacroMethods