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serialize(attr_name, class_name = Object) public

If you have an attribute that needs to be saved to the database as an object, and retrieved as the same object, then specify the name of that attribute using this method and it will be handled automatically. The serialization is done through YAML. If class_name is specified, the serialized object must be of that class on retrieval or SerializationTypeMismatch will be raised.

Parameters

  • attr_name - The field name that should be serialized.

  • class_name - Optional, class name that the object type should be equal to.

Example

# Serialize a preferences attribute
class User
  serialize :preferences
end
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November 12, 2008
6 thanks

Another Example

Do not mistakenly pass class_name as a key/value pair (Hash form). You will get an error including the text ‘class or module needed’. It should look like this:

serialize :some_array, Array

Or, perhaps clearer would be:

serialize(:some_array, Array)

That may seem obvious, but it is common to be in the habit of passing things as a key/value pair.

March 18, 2013
3 thanks

Beware - May cause performance issues

A serialized attribute will always be updated during save, even if it was not changed. (A rails 3 commit explains why: http://github.com/rails/rails/issues/8328#issuecomment-10756812)

Guard save calls with a changed? check to prevent issues.

class Product < ActiveRecord::Base
  serialize :product_data
end

bad

product = Product.first
product.save

good

product = Product.first
product.save if product.changed?
May 31, 2013
1 thank

Do not mistakenly use serialize like other similar directives - attr_accessible, attr_accessor

serialize seems very similar to other directives that work on attributes such as attr_accessible. One may mistakenly assume that serialize can take a list of attributes. For eg:

class Tuk < ActiveRecord::Base
  attr_accessible :foo, :bar
  serialize :foo, :bar
end

This may lead to a cryptic error. Eg.

puts !Tuk.first.foo.nil?

causes:

NoMethodError at /file:location undefined method `new' for :bar:Symbol

This is because it tries to parse the YAML string stored in foo as an instance of :bar.