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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
TABLE OF CONTENTS:
  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

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Callbacks and the Active Record
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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
end

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

 

 

 

 

 

Option

Description

:minimum

Specifies the minimum size of the attribute

:maximum

Specifies the maximum size of the attribute

:is

Specifies the exact size of the attribute

:within

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

:allow_nil

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

:too_long

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

:too_short

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

:wrong_length

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

:message

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

 

 

 

 

 


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