how can a controller manually set validation errors for a certain field

Question

I have a form with 3 ActiveRecord fields. One of those fields has kind of goofy, and STATE-DEPENDENT validation requirements. (For example, I only validate the field if the object is being created on a setup wizard form.)

In my POST handler to create the object, I thought I could call errors.add to insert a special error condition

@foo = Foo.new(params[:foo])
if goofy_conditions(params[:foo][:goofy_field])
  @foo.errors.add(:goofy_field, "doesn't meet the goofy conditions" )
end
respond_to do |format|
  if @foo.save
    ...
  else
    ... redirect back to form (with error fields hilited)

However, doing @foo.errors.add() in the controller doesn't seem to do anything... it doesnt prevent the save() if the other fields pass validations.

An alternative is to put a custom validation handler into the model... I know using errors.add(:field, 'msg') works fine there... but in that case how can my controller 'pass' info to the validator telling it whether or not the field needs to be validated.

Answer 1

That is model logic. Look at custom validations

class GoofyThing < ActiveRecord::Base
  validate :goofy_attribute_is_goofy

  def goofy_attribute_is_goofy
    if goofy_conditions(self.goofy_field)
      self.errors.add(:goofy_field, "doesn't meet the goofy conditions" )
    end
  end
end

Then it'll act just like any other validation.

Edit

You can conditionally validate with the :if option:

attr_accessible :via_wizard
validate :goofy_attribute_is_goofy, :if => lambda { self.via_wizard }

and in your controller:

class WizardController < ApplicationController
  before_filter :get_object, :set_wizard

  #...

  def get_object
    @object = GoofyThing.find(params[:id])
  end

  def set_wizard
    @object.via_wizard = true
  end
end