dynamic_attributes is a gem that lets you dynamically specify attributes on ActiveRecord models, which will be serialized and deserialized to a given text column. Example:

>> dm = DynamicModel.new(:field_test => 'I am a dynamic attribute')
  +-------+-------------+--------------------------------------------+
  | title | description | dynamic_attributes                         |
  +-------+-------------+--------------------------------------------+
  |       |             | {"field_test"=>"I am a dynamic_attribute"} |
  +-------+-------------+--------------------------------------------+
>> dm.field_test
  => "I am a dynamic_attribute"
>> dm.field_test2
  NoMethodError: undefined method `field_test2'
>> dm.field_test2 = 'I am too!'
  => 'I am too!'
>> dm.field_test2
  => 'I am too!'
>> dm.save
  +-------+-------------+------------------------------------------------------------------------+
  | title | description | dynamic_attributes                                                     |
  +-------+-------------+------------------------------------------------------------------------+
  |       |             | {"field_test2"=>"I am too!", "field_test"=>"I am a dynamic_attribute"} |
  +-------+-------------+------------------------------------------------------------------------+

• Rails 2.x / 3 (Tested for 2.3.5, 2.3.8 & 3).

• config.gem ‘dynamic_attributes’, sudo rake gems:install

• gem install dynamic_attributes

To add dynamic_attributes to an AR model, take the following steps:

• Create a migration to add a column to serialize the dynamic attributes to:

  class AddDynamicAttributesToDynamicModels < ActiveRecord::Migration
    def self.up
      add_column :dynamic_models, :dynamic_attributes, :text
    end
  
    def self.down
      remove_column :dynamic_models, :dynamic_attributes
    end
  end
  

• Add dynamic_attributes to your AR model:

  class DynamicModel < ActiveRecord::Base
    has_dynamic_attributes
  end
  

• Now you can add dynamic attributes in several ways. Examples:

  • New: DynamicModel.new(:title => ‘Hello’, :field_summary => ‘This is a dynamic attribute’)

  • Create: DynamicModel.create(:title => ‘Hello’, :field_summary => ‘This is a dynamic attribute’)

  • Update:

    • dynamic_model.update_attribute(:field_summary, ‘This is a dynamic attribute’)

    • dynamic_model.update_attributes(:field_summary => ‘This is a dynamic attribute’, :description => ‘Testing’)

  • Set manually: dynamic_model.field_summary = ‘This is a dynamic attribute’

Note that a dynamic attribute should be prefixed (by default with ‘field_’), see the Options section for more info.

• Get Info:

  • dynamic_model.has_dynamic_attribute?(dynamic_attribute)

    • Returns whether a given attribute is a dynamic attribute. Accepts strings and symbols.

  • dynamic_model.read_dynamic_attribute(dynamic_attribute)

    • Returns the value for a given dynamic attribute. Returns nil if the attribute does not exist or if the attribute is not a dynamic attribute.

  • dynamic_model.persisting_dynamic_attributes

    • Returns an array of the dynamic attributes that will be persisted.

  • DynamicModel.dynamic_attribute_field

    • Returns the serialization attribute. You can access this serialization attribute directly if you need to.

  • DynamicModel.dynamic_attribute_prefix

    • Returns the method prefix of dynamic attributes, see below for more info.

  • DynamicModel.destroy_dynamic_attribute_for_nil

    • Returns whether dynamic attributes with null values will be persisted, see below for more info.

The has_dynamic_attribute call takes three different options:

• :dynamic_attribute_field

  • Defines the database column to serialize to.

• :dynamic_attribute_prefix

  • Defines the prefix that a dynamic attribute should have. All attribute assignments that start with this prefix will become dynamic attributes. Note that it’s not recommended to set this prefix to the empty string; as every method call that falls through to method_missing will become a dynamic attribute.

• :destroy_dynamic_attribute_for_nil

  • When set to true, the module will remove a dynamic attribute when its value is set to nil. Defaults to false, causing the module to store a dynamic attribute even if its value is nil.

By default, the has_dynamic_attributes call without options equals to calling:

has_dynamic_attributes :dynamic_attribute_field => :dynamic_attributes, :dynamic_attribute_prefix => ‘field_’, :destroy_dynamic_attribute_for_nil => false

Take a look at the code Rdoc for more information!

The validations provided by AR can be used for dynamic attributes as if it is a normal attribute.

• Adam H. (terralab)

• 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 © 2010 Reinier de Lange. See LICENSE for details.