Validating That a Value Is Unique in Font

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Validating That a Value Is Unique
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Often, you want to make sure a certain field is unique. The :uniqueness option validates whether the value of the specified attribute is unique across the system. You use this method in the User model to make sure each e-mail is unique, as shown in Listing 5-24. Listing 5-24. validates :uniqueness => true Method in app/models/user.rb: http://gist.github.com/326128 class User < ActiveRecord::Base validates :email, :uniqueness => true has_one :profile has_many :articles, :order => 'published_at DESC, title ASC', :dependent => :nullify has_many :replies, :through => :articles, :source => :comments end When the record is created, a check is performed to make sure no record exists in the database with the given value for the specified attribute email (that maps to a column). When the record is updated,
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the same check is made, but disregarding the record itself. The default error message is #{value} has already been taken. The :uniqueness option can also validate whether the value of the specified attributes are unique based on multiple scope parameters. For example, you can use it to make sure a teacher can be on the schedule only once per semester for a particular class: class Schedule < ActiveRecord::Base validates :teacher_id, :uniqueness => { :scope => [:semester_id, :class_id] } end
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Validating Length or Size
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Sometimes you want to validate the length, or size, of a field entry. You can do this by using the :length option. You use this method in the User model to specify a valid number of characters for an e-mail address, as shown in Listing 5-25. The option for specifying a size range is :within. Listing 5-25. validates :length Method in app/models/user.rb: http://gist.github.com/326138 class User < ActiveRecord::Base validates :email, :uniqueness => true, :length => { :within => 5..50 } has_one :profile has_many :articles, :order => 'published_at DESC, title ASC', :dependent => :nullify has_many :replies, :through => :articles, :source => :comments end If you want to ensure only the minimum or maximum, you can use the :minimum or :maximum option. Table 5-8 lists the most common :length option s options. Table 5-8. Options for validates :length
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Option
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:minimum :maximum :is :within
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Description
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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 is skipped Specifies the error message to add if the attribute exceeds the maximum
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:allow_nil
:too_long
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Option
:too_short
Description
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
:wrong_length
:message
Validating the Format of an Attribute
The :format option checks whether a value is in the correct format. Using this method requires familiarity with regular expressions (regex) or being able to steal other people s regular expressions. The classic example (and the one you need) is e-mail. Update the validates method as shown in Listing 5-26. Listing 5-26. validates :format Method in app/models/user.rb: http://gist.github.com/326146 class User < ActiveRecord::Base validates :email, :uniqueness => true, :length => { :within => 5..50 }, :format => { :with => /^[^@][\w.-]+@[\w.-]+[.][a-z]{2,4}$/i } has_one :profile has_many :articles, :order => 'published_at DESC, title ASC', :dependent => :nullify has_many :replies, :through => :articles, :source => :comments end Don t be put off by how complicated this looks. You pass in the :with option and a regex object to say what patterns you want to match.
TIP If you want to learn more about using regular expressions, you can find many tutorials and books on the subject. One good reference is Regular Expression Recipes (Apress, 2004).
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