Validation is not working if integer value of old attribute is same as that of new attribute

Question

I've a model Cart having has_many relationship with cart_items.

# cart.rb:
  accepts_nested_attributes_for :cart_items, allow_destroy: true
  has_many :cart_items, dependent: :destroy, inverse_of: :cart

# cart_item.rb:
  validates :quantity, presence: true, numericality: { greater_than: 0 }

# Controller code:

  def update
    current_cart.assign_attributes(params[:cart])
    .....
    current_cart.valid?
  end

While updating cart_items, if integer (to_i) value of quantity is same as old value then validation is not working.

For example, If old value of quantity is 4, now new value is updated to 4abc then quantity validation is not working and record is considered as valid.

Although, if new value is updated from 4 to 5abc then it shows a validation error, as expected.

Any suggestions why this all is happening?

EDIT 1:

Here's the output of rails console:

[3] pry(#<Shopping::CartsController>)> cart
=> #<Cart id: 12, created_at: "2017-06-22 13:52:59", updated_at: "2017-06-23 08:54:27">

[4] pry(#<Shopping::CartsController>)> cart.cart_items
[#<CartItem id: 34201, cart_id: 12, quantity: 4, created_at: "2017-06-23 05:25:39", updated_at: "2017-06-23 08:54:27">]

[5] pry(#<Shopping::CartsController>)> param_hash
=> {"cart_items_attributes"=>{"0"=>{"id"=>"34201", "quantity"=>"4abc"}}}
[6] pry(#<Shopping::CartsController>)> cart.assign_attributes param_hash
=> nil
[7] pry(#<Shopping::CartsController>)> cart.valid?
=> true

Here, previous quantity of cart_item is 4 and new value is 4abc, but still the cart is validated.

EDIT 2:

I've checked answers of How to validate numericality and inclusion while still allowing attribute to be nil in some cases?, as it is masked as duplicate in comments, but it does not seems to work.

As I mentioned above, validation is working fine if to_i of new quantity is different than previous quantity, but if it is same then validation is not working.

Also, I tried to apply a method for custom validation using validate, but I'm getting to_i value in that method. Something like:

Model code:

validate :validate_quantity

# quantity saved in db => 4
# new quantity in form => 4abc
def validate_quantity
  puts quantity_changed? # => false
  puts quantity # => 4
end

EDIT 3:

It seems like if to_i of new value is same as previous value then model is casting the value to integer and considering the field not even updated.

EDIT 4:

I'm getting answers & comments about the pupose of to_i. I know what to_i does.

I just want to know why I'm not getting the validation error if to_i of new quantity is similar to the quantity stored in the database.

I know quantity column is integer and ActiveRecord will cast it to integer BUT there must be a validation error as I've added that in model.

I'm getting the validation error if to_i of new value is different than quantity stored in db.

BUT

I'm not getting the validation error if to_i of new value is same than quantity stored in db.

Answer 1

Since the quantity column is defined as integer, activerecord will typecast it with .to_i before assigning it to the attribute, however, quantity_changed? will be true in that case unlike what you have shown above, so that gives you a hint for solution 1, else you can check if param contains only integers or not in your controller as in solution 2.

Solution 1

validate :validate_quantity

# quantity saved in db => 4
# new quantity in form => '4abc'
def validate_quantity
  if quantity_changed?
    if quantity_was == quantity || quantity <= 0
      errors.add(:base, 'invalid quantity')
      return false
    else
      return true
    end
  else
    true
  end
end

Solution 2

In your controller,

before_action :validate_cart_params, only: [:create, :update]

private

def validate_cart_params
  unless cart_params[:quantity].scan(/\D/).empty?
    render json: { errors: "Oops! Quantity should be numeric and greater than 0." }, status: 422 and return
  end
end

UPDATE

I googled a bit, but late and found a helper _before_type_cast, it is also a good solution and @Federico has put it as a solution. I am also adding it to my list.

Solution 3

Using quantity_before_type_cast

validate :validate_quantity

# quantity saved in db => 4
# new quantity in form => '4abc'
def validate_quantity
  if quantity_changed? || ((actual_quantity = quantity_before_type_cast) != quantity_was)
    if actual_quantity.scan(/\D/).present? || quantity <= 0
      errors.add(:base, 'invalid quantity')
      return false
    else
      return true
    end
  else
    true
  end
end

Answer 2

First to answer your question why:

Problably in history it worked differently than today. Personally I suspect this commit (after a very brief search): https://github.com/rails/rails/commit/7500daec69499e4f2da2fc06cd816c754cf59504

And how to fix that?

Upgrade your rails gem... I can recommend Rails 5.0.3, which I tested and it works as expected.

Answer 3

Following the source code for numeric validation, it casts Integer type on the string

"4abc".to_i
=> 4

Hence the input is greater then 0

To resolve it, try to use <input type="numeric" /> in your view to force a user to type only integer values

Answer 4

You should use quantity_before_type_cast, as explained here, in section "Accessing attributes before they have been typecasted". For example:

validate :validate_quantity

# quantity saved in db => 4
# new quantity in form => 4abc
def validate_quantity
  q = quantity_before_type_cast
  return if q == q.to_i
  errors.add(:quantity, 'invalid quantity') unless (q.to_i.to_s == q)
end

Answer 5

This type of issue is already reported in Github.

Reported issues:

• Parent model not marked as invalid when associated record is invalid, but not dirty
• Validations not triggered when attribute is changed from 0 to a string if it's a nested attribute
• Validates_numericality_of skipped when changing 0 to "foo" through accepts_nested_attributes_for

Fixed in:

[v4.0]

• https://github.com/rails/rails/commit/b9ec47da00e7f5e159ff130441585c3b42e41849

[v3.2]

• https://github.com/rails/rails/commit/40617c7e539b8b70469671619e3c1716edcfbf59

All the issues are reported where previous value of an integer attribute is 0 and new value is some string (whose to_i will be 0). Thus the fix is also only for 0.

You can check the same in #changes_from_zero_to_string? in active_record/attribute_methods/dirty.rb, which is initially called from #_field_changed?

---

Solution:

Override #_field_changed? specifically for quantity field only (due to lack of time. In future, I'll override method for all integer fields).

Now if to_i value of some alphanumeric quantity is equal to current quantity value in database then below method will return true and will not type cast the value.

def _field_changed?(attr, old, value)
  if attr == 'quantity' && old == value.to_i && value != value.to_i.to_s
    return true
  end

  super
end

Answer 6

to_i(p1 = v1) public

Returns the result of interpreting leading characters in str as an integer base (between 2 and 36). Extraneous characters past the end of a valid number are ignored. If there is not a valid number at the start of str, 0 is returned. This method never raises an exception when the base is valid.

"12345".to_i             #=> 12345
"99 red balloons".to_i   #=> 99
"0a".to_i                #=> 0
"0a".to_i(16)            #=> 10
"hello".to_i             #=> 0
"1100101".to_i(2)        #=> 101
"1100101".to_i(8)        #=> 294977
"1100101".to_i(10)       #=> 1100101
"1100101".to_i(16)       #=> 17826049

The problem happens because

"4".to_i => 4
"4abc".to_i => 4

That means your custom validation will pass and will not cause any error on the page.

Hope that helps you...