has_one_attached (name, dependent: :purge_later, service: nil, strict_loading: false)
public
Specifies the relation between a single attachment and the model.
class User < ApplicationRecord has_one_attached :avatar
end
There is no column defined on the model side, Active Storage takes care of
the mapping between your records and the attachment.
To avoid N+1 queries, you can include the attached blobs in your query like
so:
User . with_attached_avatar
Under the covers, this relationship is implemented as a has_one
association to a ActiveStorage::Attachment record
and a has_one-through association to a ActiveStorage::Blob record. These
associations are available as avatar_attachment and
avatar_blob . But you shouldn’t need to work with these
associations directly in most circumstances.
The system has been designed to having you go through the ActiveStorage::Attached::One
proxy that provides the dynamic proxy to the associations and factory
methods, like attach .
If the :dependent option isn’t set, the attachment will be
purged (i.e. destroyed) whenever the record is destroyed.
If you need the attachment to use a service which differs from the globally
configured one, pass the :service option. For instance:
class User < ActiveRecord :: Base
has_one_attached :avatar , service : :s3
end
If you need to enable strict_loading to prevent lazy loading of
attachment, pass the :strict_loading option. You can do:
class User < ApplicationRecord has_one_attached :avatar , strict_loading : true
end Show source # File activestorage/lib/active_storage/attached/model.rb, line 94
def has_one_attached(name, dependent: :purge_later, service: nil, strict_loading: false)
validate_service_configuration(name, service)
generated_association_methods.class_eval # 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, __FILE__, __LINE__ + 1
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: %[ 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