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Provides the class-level DSL for declaring an Active Record model's attachments.

Methods
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P
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Instance Public methods
has_many_attached(name, dependent: :purge_later, service: nil)

Specifies the relation between multiple attachments and the model.

class Gallery < ApplicationRecord
  has_many_attached :photos
end

There are no columns defined on the model side, Active Storage takes care of the mapping between your records and the attachments.

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

Gallery.where(user: Current.user).with_attached_photos

Under the covers, this relationship is implemented as a has_many association to a ActiveStorage::Attachment record and a has_many-through association to a ActiveStorage::Blob record. These associations are available as photos_attachments and photos_blobs. 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::Many proxy that provides the dynamic proxy to the associations and factory methods, like #attach.

If the :dependent option isn't set, all the attachments 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 Gallery < ActiveRecord::Base
  has_many_attached :photos, service: :s3
end
# File activestorage/lib/active_storage/attached/model.rb, line 112
      def has_many_attached(name, dependent: :purge_later, service: nil)
        validate_service_configuration(name, service)

        generated_association_methods.class_eval <<-CODE, __FILE__, __LINE__ + 1
          def #{name}
            @active_storage_attached_#{name} ||= ActiveStorage::Attached::Many.new("#{name}", self)
          end

          def #{name}=(attachables)
            if ActiveStorage.replace_on_assign_to_many
              attachment_changes["#{name}"] =
                if Array(attachables).none?
                  ActiveStorage::Attached::Changes::DeleteMany.new("#{name}", self)
                else
                  ActiveStorage::Attached::Changes::CreateMany.new("#{name}", self, attachables)
                end
            else
              if Array(attachables).any?
                attachment_changes["#{name}"] =
                  ActiveStorage::Attached::Changes::CreateMany.new("#{name}", self, #{name}.blobs + attachables)
              end
            end
          end
        CODE

        has_many :"#{name}_attachments", -> { where(name: name) }, as: :record, class_name: "ActiveStorage::Attachment", inverse_of: :record, dependent: :destroy do
          def purge
            each(&:purge)
            reset
          end

          def purge_later
            each(&:purge_later)
            reset
          end
        end
        has_many :"#{name}_blobs", through: :"#{name}_attachments", class_name: "ActiveStorage::Blob", source: :blob

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

        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_many_attached,
          name,
          nil,
          { dependent: dependent, service_name: service },
          self
        )
        ActiveRecord::Reflection.add_attachment_reflection(self, name, reflection)
      end
has_one_attached(name, dependent: :purge_later, service: nil)

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
# File activestorage/lib/active_storage/attached/model.rb, line 43
      def has_one_attached(name, dependent: :purge_later, service: nil)
        validate_service_configuration(name, service)

        generated_association_methods.class_eval <<-CODE, __FILE__, __LINE__ + 1
          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
        CODE

        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: %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
        )
        ActiveRecord::Reflection.add_attachment_reflection(self, name, reflection)
      end
purge()
# File activestorage/lib/active_storage/attached/model.rb, line 138
def purge
  each(&:purge)
  reset
end
purge_later()
# File activestorage/lib/active_storage/attached/model.rb, line 143
def purge_later
  each(&:purge_later)
  reset
end
validate_service_configuration(association_name, service)
# File activestorage/lib/active_storage/attached/model.rb, line 167
def validate_service_configuration(association_name, service)
  return unless service

  ServiceRegistry.fetch(service) do
    raise ArgumentError, "Cannot configure service :#{service} for #{name}##{association_name}"
  end
end