module ActiveStorage::Attached::Model

the corresponding rows.
active_storage_attachments.record_type polymorphic type column of
When renaming classes that use has_one_attached, make sure to also update the class names in the
Note: Active Storage relies on polymorphic associations, which in turn store class names in the database.

end
has_one_attached :avatar, strict_loading: true
class User < ApplicationRecord

pass the +:strict_loading+ option. You can do:
If you need to enable +strict_loading+ to prevent lazy loading of attachment,

User.with_attached_avatar

To avoid N+1 queries, you can include the attached blobs in your query like so:

end
has_one_attached :avatar, service: ->(user) { user.in_europe_region? ? :s3_europe : :s3_usa }
class User < ActiveRecord::Base

+:service+ can also be specified as a proc, and it will be called with the model instance:

end
has_one_attached :avatar, service: :s3
class User < ActiveRecord::Base

pass the +:service+ option. For example:
If you need the attachment to use a service which differs from the globally configured one,

+purge+ instead.
If an ActiveJob::Backend queue adapter is not set in the application set it to
purged (i.e. destroyed) in the background whenever the record is destroyed.
The +:dependent+ option defaults to +:purge_later+. This means the attachment will be

user.avatar.attach(uploaded_file)

provide access to the associations and factory methods, like +attach+:
Instead, +has_one_attached+ generates an ActiveStorage::Attached::One proxy to

most circumstances.
and +avatar_blob+. But you shouldn't need to work with these associations directly in
ActiveStorage::Blob record. These associations are available as +avatar_attachment+
ActiveStorage::Attachment record and a +has_one-through+ association to a
Under the covers, this relationship is implemented as a +has_one+ association to a

care of the mapping between your records and the attachment.
There is no column defined on the model side, Active Storage takes

end
has_one_attached :avatar
class User < ApplicationRecord

Specifies the relation between a single attachment and the model.

def has_one_attached(name, dependent: :purge_later, service: nil, strict_loading: false)
  ActiveStorage::Blob.validate_service_configuration(service, self, name) unless service.is_a?(Proc)
  generated_association_methods.class_eval <<-CODE, __FILE__, __LINE__ + 1
    # frozen_string_literal: true
    def #{name}
      @active_storage_attached ||= {}
      @active_storage_attached[:#{name}] ||= ActiveStorage::Attached::One.new("#{name}", self)
    end
    def #{name}=(attachable)
      attachment_changes["#{name}"] =
        if attachable.nil? || attachable == ""
          ActiveStorage::Attached::Changes::DeleteOne.new("#{name}", self)
        else
          ActiveStorage::Attached::Changes::CreateOne.new("#{name}", self, attachable)
        end
    end
  CODE
  has_one :"#{name}_attachment", -> { where(name: name) }, class_name: "ActiveStorage::Attachment", as: :record, inverse_of: :record, dependent: :destroy, strict_loading: strict_loading
  has_one :"#{name}_blob", through: :"#{name}_attachment", class_name: "ActiveStorage::Blob", source: :blob, strict_loading: strict_loading
  scope :"with_attached_#{name}", -> {
    if ActiveStorage.track_variants
      includes("#{name}_attachment": { blob: {
        variant_records: { image_attachment: :blob },
        preview_image_attachment: { blob: { variant_records: { image_attachment: :blob } } }
      } })
    else
      includes("#{name}_attachment": :blob)
    end
  }
  after_save { attachment_changes[name.to_s]&.save }
  after_commit(on: %i[ create update ]) { attachment_changes.delete(name.to_s).try(:upload) }
  reflection = ActiveRecord::Reflection.create(
    :has_one_attached,
    name,
    nil,
    { dependent: dependent, service_name: service },
    self
  )
  yield reflection if block_given?
  ActiveRecord::Reflection.add_attachment_reflection(self, name, reflection)
end