Rails accepts_nested_attributes count validation

Question

I've got three models. Sales, items, and images. I'd like to validate that when a sale is created there are at least three photos per sale and one or more items. What would be the best way to achieve this?

Sales Model:

class Sale < ActiveRecord::Base
   has_many :items, :dependent => :destroy
   has_many :images, :through => :items

   accepts_nested_attributes_for :items, :reject_if => lambda { |a| a[:title].blank? }, :allow_destroy => true
end

Items Model:

class Item < ActiveRecord::Base

  belongs_to :sale, :dependent => :destroy
  has_many :images, :dependent => :destroy

  accepts_nested_attributes_for :images

end

Images Model:

class Image < ActiveRecord::Base
  belongs_to :item, :dependent => :destroy
end

Donavan White · Accepted Answer · 2015-01-16T22:51:51.717

9

Create custom methods for validating

In your sales model add something like this:

validate :validate_item_count, :validate_image_count

def validate_item_count
  if self.items.size < 1
    errors.add(:items, "Need 1 or more items")
  end
end

def validate_image_count
  if self.items.images.size < 3
    errors.add(:images, "Need at least 3 images")
  end
end

Hope this helps at all, good luck and happy coding.

edited Jan 16 '15 at 22:51

answered Mar 29 '12 at 21:10

Donavan White

1,126
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2

ideally name these methods validate_item_count and validate_image_count because this clarifies your intent and that the methods add errors. – joelparkerhenderson Mar 29 '12 at 21:17
Hm, this isn't working for me on creation of a new record. – alex May 08 '21 at 22:20
Ah, don't worry. I was querying the ActiveRecord association from a *third* layer of nested_attributes. Got it working by querying the initial nested_attributes instead. – alex May 08 '21 at 22:26
1

@alex Glad after 9 years, this is still helpful for people :) – Donavan White May 11 '21 at 01:05
@DonavanWhite Absolutely! – alex May 11 '21 at 11:34

score 4 · Answer 2 · answered Sep 07 '13 at 23:53

Another option is using this little trick with the length validation. Although most examples show it being used with text, it will check the length of associations as well:

class Sale < ActiveRecord::Base
   has_many :items,  dependent: :destroy
   has_many :images, through: :items

   validates :items,  length: { minimum: 1, too_short: "%{count} item minimum" }
   validates :images, length: { minimum: 3, too_short: "%{count} image minimum" }
end

You just need to provide your own message as the default message mentions a character count.

Rails accepts_nested_attributes count validation

2 Answers2

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