validates_numericality_of

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

The following checks can also be supplied with a proc or a symbol which corresponds to a method:

• :greater_than
• :greater_than_or_equal_to
• :equal_to
• :less_than
• :less_than_or_equal_to

  class Person < ActiveRecord::Base

    validates_numericality_of :width, :less_than => Proc.new { |person| person.height }
    validates_numericality_of :width, :greater_than => :minimum_weight
  

  end