Data Attributes¶ ↑

A gem for easy access to attributes stored in a serialized data hash.

ActiveRecord attributes are mapped to columns in your database; however, many attributes that needed to be persisted for an object don’t need their own column because they will never be searched or filtered on. One solution is to save these with a serialized hash into a text field in the database and provide similar access to the values as other attribute accessors.

Consider a User class that has a text field that is serialized, data.

class User < ActiveRecord::Base

  serialize :data

end

We can set an accessor to an attribute to be saved in the data field with the following:

data_attribute :details

This generates a read and write accessor called details.

u = User.new
u.details = "I don't need to query on this."
puts u.details
=> I don't need to query on this.
puts u.data.inspect
=> { "details" => "I don't need to query on this." }

The default serialized attribute used is data. There are two ways to change the serialized attribute used for storage. The first is set a different default attribute for the class.

data_attribute_column :more_data

This makes all of the accessors created with data_attributes be saved in more_data instead of data. If a class has two (or more) serialized attributes that will share the storage responsibilities, each attribute defined with data_attributes can be individually assigned to a serialized attribute by using a hash.

data_attribute :details, { :serialized_column => :more_data }

This creates an accessor that saves details to more_data.

You can set a default to be returned, in the case the value hasn’t be set yet.

data_attribute :details, { :default => "default value" }

Like column accessors that make use of read_attribute and write_attribute, data-attributes uses read_data_attribute and write_data_attribute to access the serialized attribute. This allows the ability to overwrite an accessor so any validation or other data manipulation needed before the value is returned or saved.

Copyright © 2011 Les Fletcher

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