Validation for the count of has_many relationship in Rails -

i have been through other questions, scenario little different here:

class user < applicationrecord   has_many :documents, as: :attachable    validate :validate_no_of_documents    private   def validate_no_of_documents     errors.add(:documents, "count shouldn't more 2") if self.documents.size > 2   end end   class document < applicationrecord   belongs_to :attachable, polymorphic: true    validates_associated :attachable end 

now, consider user.find(2) has 2 documents, doing following:

user.documents << document.new(file: file.open('image.jpg', 'rb')) 

this creates document, , doesn't validate attachable: user. after document created in database, both user & document.last invalid, of use, have been created now.

i'm trying create document object on run time, , may causing it, purpose, i'm using size instead of count in validation.

inverse_of rescue here again.

user = user.find(1) # user has 2 associated documents.  

doing user.documents << document.new(file: file) won't change count associated documents of user unless document created, , since count remain 2 while creating 3rd document, rails won't stop creating third document associated user, killing purpose of putting validation.

so following did:

# in user model has_many :documents, as: :attachable, inverse_of: :attachable  # in document model belongs_to :attachable, polymorphic: true, inverse_of: :attachments 

related article read: https://robots.thoughtbot.com/accepts-nested-attributes-for-with-has-many-through