validates_presence_of(*attr_names) public

Validates that the specified attributes are not blank (as defined by Object#blank?). Happens by default on save. Example:

  class Person < ActiveRecord::Base
    validates_presence_of :first_name

The first_name attribute must be in the object and it cannot be blank.

Configuration options:

  • message - A custom error message (default is: "can’t be blank")
  • on - Specifies when this validation is active (default is :save, other options :create, :update)
  • 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.


Validate the presence of the foreign key, not the instance variable itself. Do this:

 validate_presence_of :invoice_id

Not this:

 validate_presence_of :invoice

If you validate the presence of the associated object, you will get failures on saves when both the parent object and the child object are new.

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