Validates whether the value of the specified attribute is numeric by trying to convert it to a float with Kernel.Float (if integer is false) or applying it to the regular expression /\A[+\-]?\d+\Z/ (if integer is set to true).

class Person < ActiveRecord::Base
  validates_numericality_of :value, :on => :create
end

Configuration options:

• message - A custom error message (default is: "is not a number")
• on Specifies when this validation is active (default is :save, other options :create, :update)
• only_integer Specifies whether the value has to be an integer, e.g. an integral value (default is false)
• allow_nil Skip validation if attribute is nil (default is false). Notice that for fixnum and float columns empty strings are converted to nil
• greater_than Specifies the value must be greater than the supplied value
• greater_than_or_equal_to Specifies the value must be greater than or equal the supplied value
• equal_to Specifies the value must be equal to the supplied value
• less_than Specifies the value must be less than the supplied value
• less_than_or_equal_to Specifies the value must be less than or equal the supplied value
• odd Specifies the value must be an odd number
• even Specifies the value must be an even number
• if - Specifies a method, proc or string to call to determine if the validation should occur (e.g. :if => :allow_validation, or :if => Proc.new { |user| user.signup_step > 2 }). The method, proc or string should return or evaluate to a true or false value.
• unless - Specifies a method, proc or string to call to determine if the validation should not occur (e.g. :unless => :skip_validation, or :unless => Proc.new { |user| user.signup_step <= 2 }). The method, proc or string should return or evaluate to a true or false value.

Source Code

# File active_record/validations.rb, line 860
def validates_numericality_of(*attr_names)
  configuration = { :on => :save, :only_integer => false, :allow_nil => false }
  configuration.update(attr_names.extract_options!)


  numericality_options = ALL_NUMERICALITY_CHECKS.keys & configuration.keys

  (numericality_options - [ :odd, :even ]).each do |option|
    raise ArgumentError, ":#{option} must be a number" unless configuration[option].is_a?(Numeric)
  end

  validates_each(attr_names,configuration) do |record, attr_name, value|
    raw_value = record.send("#{attr_name}_before_type_cast") || value

    next if configuration[:allow_nil] and raw_value.nil?

    if configuration[:only_integer]
      unless raw_value.to_s =~ /\A[+-]?\d+\Z/
        record.errors.add(attr_name, configuration[:message] || ActiveRecord::Errors.default_error_messages[:not_a_number])
        next
      end
      raw_value = raw_value.to_i
    else
     begin
        raw_value = Kernel.Float(raw_value.to_s)
      rescue ArgumentError, TypeError
        record.errors.add(attr_name, configuration[:message] || ActiveRecord::Errors.default_error_messages[:not_a_number])
        next
      end
    end

    numericality_options.each do |option|
      case option
        when :odd, :even
          record.errors.add(attr_name, configuration[:message] || ActiveRecord::Errors.default_error_messages[option]) unless raw_value.to_i.method(ALL_NUMERICALITY_CHECKS[option])[]
        else
          record.errors.add(attr_name, configuration[:message] || (ActiveRecord::Errors.default_error_messages[option] % configuration[option])) unless raw_value.method(ALL_NUMERICALITY_CHECKS[option])[configuration[option]]
      end
    end
  end
end