Controlling the order of rails validations

Question

I have a rails model which has 7 numeric attributes filled in by the user via a form.

I need to validate the presence of each of these attributes which is obviously

Answer 1

An alternative for slightly more complex situations would be to create a helper method which runs the validations for the dependent attributes first. Then you can make your :calculations_ok? validation run conditionally.

validates :attribute1, :presence => true
validates :attribute2, :presence => true
...
validates :attribute7, :presence => true

validate :calculations_ok?, :unless => Proc.new { |a| a.dependent_attributes_valid? }

def dependent_attributes_valid?
  [:attribute1, ..., :attribute7].each do |field|
    self.class.validators_on(field).each { |v| v.validate(self) }
    return false if self.errors.messages[field].present?
  end
  return true
end

I had to create something like this for a project because the validations on the dependent attributes were quite complex. My equivalent of :calculations_ok? would throw an exception if the dependent attributes didn't validate properly.

Advantages:

• relatively DRY, especially if your validations are complex
• ensures that your errors array reports the right failed validation instead of the macro-validation
• automatically includes any additional validations on the dependent attributes you add later

Caveats:

• potentially runs all validations twice
• you may not want all validations to run on the dependent attributes