How to validate uniqueness of field before save, if field is changed before save?

I have a User model that needs to validate the uniqueness of a field before it is saved, this field however, is changed before it is saved (it is hashed). How can I do this? I tried the following: Adding a validate digest at the end of the before save call, but that doesn’t work.

class User < ApplicationRecord        
  has_secure_password
                                                
  before_save :downcase_email, :downcase_name, :digest_email, :validate_email_digest
                                                                             
  validates :email, format: { with: URI::MailTo::EMAIL_REGEXP }, presence: true 
  validates :name, length: { within: 2..40 }, presence: true, uniqueness: true
  validates :password_digest, presence: true
                                                               
  self.implicit_order_column = 'created_at'

  private     
                                   
  def validate_email_digest
    # This throws an exception                                  
    validates_uniqueness_of :email, message: 'That email is already in use.'
  end
  
  def downcase_email
    self.email = email.downcase
  end

  def downcase_name
    self.name = name.downcase
  end

  def digest_email
    self.email = Digest::SHA2.hexdigest(email).to_s
  end
end

How can I validate the result of the model before_save before they are saved to the database? In this case how can I validate that the digested email is unique after it’s been digested by before_save :digest_email?

>Solution :

Just change the before_save callback into a before_validation callback.