method

has_one_attached

v6.0.0 - Show latest stable - Class: ActiveStorage::Attached::Model

has_one_attached(name, dependent: :purge_later)

public

Specifies the relation between a single attachment and the model.

class User < ActiveRecord::Base
  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.

# File activestorage/lib/active_storage/attached/model.rb, line 33
      def has_one_attached(name, dependent: :purge_later)
        generated_association_methods.class_eval           def #{name}            @active_storage_attached_#{name} ||= ActiveStorage::Attached::One.new("#{name}", self)          end          def #{name}=(attachable)            attachment_changes["#{name}"] =              if attachable.nil?                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
        has_one :"#{name}_blob", through: :"#{name}_attachment", class_name: "ActiveStorage::Blob", source: :blob

        scope :"with_attached_#{name}", -> { includes("#{name}_attachment": :blob) }

        after_save { attachment_changes[name.to_s]&.save }

        after_commit(on: %[ create update ]) { attachment_changes.delete(name.to_s).try(:upload) }

        ActiveRecord::Reflection.add_attachment_reflection(
          self,
          name,
          ActiveRecord::Reflection.create(:has_one_attached, name, nil, { dependent: dependent }, self)
        )
      end

has_one_attached

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