Home arrow Ruby-on-Rails arrow Callbacks and the Active Record

Callbacks and the Active Record

In this conclusion to a five-part series that delves into the Rails framework's Active Record, you'll finish learning about validations, and take a look at callbacks. This article is excerpted from chapter five of the book Beginning Rails: From Novice to Professional, written by Jeffrey Allan Hardy, Cloves Carneiro Jr. and Hampton Catlin (Apress; ISBN: 1590596862).

Author Info:
By: Apress Publishing
Rating: 5 stars5 stars5 stars5 stars5 stars / 2
February 25, 2010
  1. · Callbacks and the Active Record
  2. · Validating the Format of an Attribute
  3. · Making Callbacks
  4. · Reviewing the Updated Models
  5. · Updating the User Model

print this article

Callbacks and the Active Record
(Page 1 of 5 )

Validating the Length or Size

Sometimes you want to validate the length, or size, of a field entry. You can do this by using thevalidates_length_ofmethod. We’ll use this method in ourUsermodel to specify a valid range of characters for a login name, as shown in Listing 5-22. The option for specifying a range of values is:within.

Listing 5-22. validates_length_of Method, in app/models/user.rb

class User < ActiveRecord::Base 
  validates_length_of :login, :within => 4..40

If you want to ensure only the minimum or maximum, you can use the:minimumor:maximumattributes. Table 5-7 lists thevalidates_length_ofmethod options.

Table 5-7. Options for validates_length_of









Specifies the minimum size of the attribute


Specifies the maximum size of the attribute


Specifies the exact size of the attribute


Specifies the valid range (as a Ruby Range object) of values acceptable for the attribute 


Specifies that the attribute may be nil; if so, the validation will be skipped. 


Specifies the error message to add if the attribute exceeds the maximum.


Specifies the error message to add if the attribute is below the minimum.


Specifies the error message to add if the attribute is of the wrong size


Specifies the error message to add if :minimum, :maximum, or :is is violated.






blog comments powered by Disqus

- Ruby-on-Rails Faces Second Security Flaw in ...
- Ruby 2.0 Prepped for February 2013 Release
- Why LinkedIn Switched from Ruby on Rails
- Adding Style with Action Pack
- Handling HTML in Templates with Action Pack
- Filters, Controllers and Helpers in Action P...
- Action Pack and Controller Filters
- Action Pack Categories and Events
- Logging Out, Events and Templates with Actio...
- Action Pack Sessions and Architecture
- More on Action Pack Partial Templates
- Action Pack Partial Templates
- Displaying Error Messages with the Action Pa...
- Action Pack Request Parameters
- Creating an Action Pack Registration Form

Watch our Tech Videos 
Dev Articles Forums 
 RSS  Articles
 RSS  Forums
 RSS  All Feeds
Write For Us 
Weekly Newsletter
Developer Updates  
Free Website Content 
Contact Us 
Site Map 
Privacy Policy 

Developer Shed Affiliates


© 2003-2019 by Developer Shed. All rights reserved. DS Cluster - Follow our Sitemap
Popular Web Development Topics
All Web Development Tutorials