Nested attributes won't validate multiple times but will run validation hooks multiple times for many_to_one relationships

[benalavi]

In the example below the before_validation and after_validation hooks are run twice when using nested_attributes to create associated records with a many_to_one relationship (tracks on album_tracks), but the hooks are run once when using nested_attributes to create associated records with a one_to_many relationship (artists on albums).

I was surprised that the before_validation and after_validation hooks would run at all when validate is not going to run, but that looks purposeful (https://github.com/jeremyevans/sequel/blob/master/lib/sequel/model/base.rb#L1972-L1974), so not sure whether this is a bug or a just something to be aware of.

# frozen_string_literal: true

require "bundler"
Bundler.setup

require "sequel"
DB = Sequel.sqlite

Sequel.extension :migration

Sequel.migration do
  up do
    create_table :artists do
      primary_key :id

      foreign_key :album_id, :albums, null: false

      column :name, :text, null: false
    end

    create_table :albums do
      primary_key :id
    end

    create_table :album_tracks do
      primary_key :id

      foreign_key :album_id, :albums, null: false
      foreign_key :track_id, :tracks, null: false

      column :sequence, :integer, null: false
    end

    create_table :tracks do
      primary_key :id

      column :title, :text, null: false
    end
  end
end.apply DB, :up

class Artist < Sequel::Model
  attr_reader \
    :before_validation_side_effects,
    :validate_side_effects,
    :after_validation_side_effects

  protected

  def before_validation
    @before_validation_side_effects ||= 0
    @before_validation_side_effects += 1

    super
  end

  def validate
    @validate_side_effects ||= 0
    @validate_side_effects += 1

    super
  end

  def after_validation
    super

    @after_validation_side_effects ||= 0
    @after_validation_side_effects += 1
  end
end

class Album < Sequel::Model
  plugin :nested_attributes

  one_to_many :album_tracks
  nested_attributes :album_tracks

  one_to_many :artists
  nested_attributes :artists
end

class AlbumTrack < Sequel::Model
  plugin :nested_attributes

  many_to_one :track
  nested_attributes :track
end

class Track < Sequel::Model
  attr_reader \
    :before_validation_side_effects,
    :validate_side_effects,
    :after_validation_side_effects

  protected

  def before_validation
    @before_validation_side_effects ||= 0
    @before_validation_side_effects += 1

    super
  end

  def validate
    @validate_side_effects ||= 0
    @validate_side_effects += 1

    super
  end

  def after_validation
    super

    @after_validation_side_effects ||= 0
    @after_validation_side_effects += 1
  end
end

album = Album.create \
  artists_attributes: [{
    name: "Steve"
  }],
  album_tracks_attributes: [{
    sequence: 1,
    track_attributes: {
      title: "Track 1"
    }
  }]

puts "nested artists"
album.artists.each{ puts it.before_validation_side_effects } #=> 1
album.artists.each{ puts it.validate_side_effects } #=> 1
album.artists.each{ puts it.after_validation_side_effects } #=> 1

puts "nested album_tracks"
album.album_tracks.each{ puts it.track.before_validation_side_effects } #=> 2
album.album_tracks.each{ puts it.track.validate_side_effects } #=> 1
album.album_tracks.each{ puts it.track.after_validation_side_effects } #=> 2

[benalavi]

Ah! I found that this behavior is also documented here: https://sequel.jeremyevans.net/rdoc/files/doc/model_hooks_rdoc.html#label-Available+Hooks

[jeremyevans]

Yes. This is expected behavior. The reason for this is that both plugin code as well as a significant number of models may need to run code necessary to save the object before validations are run, which shouldn't be skipped even if validations are skipped. I considered various ways to handle that, but the simplest is to just have the validation hooks always run, even if validation itself is skipped.

[benalavi]

I see, thanks for the clarification.

In case it is helpful our case was simple to fix by moving the code we wanted to avoid running multiple times from before_validation into the beginning of the validate hook.