custom rails validations

Question

I'm not sure what the best way to implement this is--basically I would like to check if my :start_amount field of my model is within a range from 0 to user.amount. I'm not sure how to say 'user.amount' since it's not static like the other validations.

(for reference I did validates_numericality_of :start_amount, :allow_nil => false, :greater_than => 0

and then did this in the same model:

def validates
    self.errors.add(:start_amount, "is out of range") unless self.amount_in_allowed_range
  end

  def amount_in_allowed_range
    start_amount <= user.amount
  end

It's pretty simple so I didn't think creating another class for the validation was needed (maybe that's the only way it works?) It was working ok except when I left start_amount blank, in which case it was comparing nil <= user.amount and gave an error (which I think is weird, since it should be checking for that in the validates_numericality_of--but I guess the custom validation runs first). Then I changed it to the above with :allow_nil => false and also set it as :null => false, :default => 0 in my migrations. now it just doesn't seem to check at all? or it's permanently 0, and thus always passes validation...)

I'm really new to rails and would appreciate any help. Thanks!

fflyer05 · Accepted Answer · 2010-12-20 18:49:52Z

4

validates_numericality_of :start_amount
validate :amount_in_allowed_range

def amount_in_allowed_range
   self.errors.add(:start_amount, "is out of range") unless start_amount <= self.user.amount
end

That should work if your current model has a belongs_to relationship to user. Note that custom validation methods are declared singular (validate instead of validates). Also, allow_nil is false by default. And I am not sure why :default => 0 was set in your routes? Did you mean migrations? Please give a bit more detail about what your setup looks like. What sort of error were you getting when nil was compared to user.amount?

edited Dec 20, 2010 at 18:49

answered Dec 20, 2010 at 7:40

fflyer05

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2 Comments

butterywombat Over a year ago

Ah yes I meant migrations, not routes for :default =>0 (corrected it). When I use what you suggested there is no change--it's as if there is no custom validation. I used def validates because it seemed like that was the default custom validation name. How could you a raise a custom error without the .errors.add? The error was a NoMethodError when nil was compared to user.amount.

fflyer05 Over a year ago

You are right, you need errors.add and it needed to be conditional. I edited the method to reflect it

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