Ruby on Rails

Validating UK postcodes with ActiveRecord validations

Posted on by Jason Neylon

Validating UK postcodes with ActiveRecord is pretty straightforward. I grabbed a regular expression from this blog post and made it slightly more forgiving to accept postcodes without spaces (so that it accepts both SW1 1AB and SW11AB).

Here is a version with the regular expression inline:

class Address < ActiveRecord::Base
attr_accessible :postcode
validates_format_of :postcode, :with => /^([A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKS-UW])\s?[0-9][ABD-HJLNP-UW-Z]{2}|(GIR\ 0AA)|(SAN\ TA1)|(BFPO\ (C\/O\ )?[0-9]{1,4})|((ASCN|BBND|[BFS]IQQ|PCRN|STHL|TDCU|TKCA)\ 1ZZ))$$/i, :message => "invalid postcode"
end

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address.rb
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And here is the custom validator version:

class PostcodeValidator < ActiveModel::EachValidator
def validate_each(record, attribute, value)
unless value =~ /^([A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKS-UW])\s?[0-9][ABD-HJLNP-UW-Z]{2}|(GIR\ 0AA)|(SAN\ TA1)|(BFPO\ (C\/O\ )?[0-9]{1,4})|((ASCN|BBND|[BFS]IQQ|PCRN|STHL|TDCU|TKCA)\ 1ZZ))$$/i
record.errors[attribute] << (options[:message] || "invalid postcode")
end
end
end

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postcode_validator.rb
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To use the custom validator bung the file in app/validators/ and use like so:

class Address < ActiveRecord::Base
attr_accessible :postcode
validates :postcode, :postcode => true
end

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address.rb
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