ActiveModel validate custom setter

Question

Say I have a custom setter on an activemodel model DateRange, to automatically set a DateTime attribute if a string is entered. It looks like this

  def from=(value)
    @from = value.to_date
  end

Now this does work if you enter a valid date string, but if you enter an invalid date, it stalls my application. How can I cancel assignment so that the application will move on and the DateRange fails validation later on in my controller?

if i enter an invalid date, but in correct format, eg '13/13/2010', i get an ArgumentError (invalid date), but if i enter a malicious string eg 'not a date' i get NoMethodError — Marco Prins, Mar 04 '14 at 12:03

score 3 · Accepted Answer · answered Mar 04 '14 at 12:14

3

def from=(value)
  begin
    @from = value.to_date
  rescue ArgumentError, NoMethodError
    errors.add(:from, "is not a valid date")
  end
end

Probably a better way to do it but that should work

answered Mar 04 '14 at 12:14

j-dexx

10,286
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1

Problem with this is that doesn't prevent the attribute from being saved (with a `from` attribute as it was previously). For that I've found you need to encapsulate this logic inside a validator: http://stackoverflow.com/a/9676246/1755300 – unmultimedio Nov 29 '16 at 20:50
2

This solution is NOT correct. Calling `valid?` would completely ignore the added error and the model can be created/updated. – Itay Grudev May 31 '17 at 10:32
1

This will not work because `valid?` will [clean](https://github.com/rails/rails/blob/v6.0.3.2/activemodel/lib/active_model/validations.rb#L336) `errors` before performing actual validation callbacks – Kirill Aug 19 '20 at 12:57

score 2 · Answer 2 · answered Mar 04 '14 at 12:49

2

You would generally want to rescue/handle any problem in your setter.

def from=(value)
  @from = Date.parse(value)
rescue ArgumentError
  nil
end

Then let your normal date validations handle the nil value later.

I wouldn't add to your errors in the setter as it should not need to know about your validations and vice versa.

answered Mar 04 '14 at 12:49

jordelver

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Wouldn't that be confusing to a user though as it would say it can't be blank (assuming validating presence) even though they input something? – j-dexx Mar 04 '14 at 13:20

score 1 · Answer 3 · answered Feb 19 '18 at 19:28

1

As @jordelver says, there is no point in adding validation errors except during validation. However, you can save the error in a virtual attribute and check for it during validation.

validate :no_bad_dates
attr_accessor :bad_date_error

def from=(value)
  @from = Date.parse(value)
rescue ArgumentError => ex
  self.bad_date_error = ex
end

def no_bad_dates()
  errors.add(:from, bad_date_error.message) if bad_date_error
end

answered Feb 19 '18 at 19:28

Tom Wilson

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Note that `bad_date_error` does not need to be publicly accessible. Implemented here as `attr_accessor` to simplify the story. – Tom Wilson Feb 20 '18 at 18:45

ActiveModel validate custom setter

3 Answers3