How to avoid destroy deleting earlier related object - ruby-on-rails

Question

If the user already has a favorite model after log in, then I want the products that were added to their anonymous bookmarks to be overwritten in the favorite that is attached to their user object.
I find session_favorite (anonymous favorite), #favorite, which belongs to the user. I am rewriting line_item.favorite with the ID of session_favorite to the user's ID favorite. I reset the session and destroy that anonymous favorite, which in theory has become empty, since now line_items has the user's favorite ID.
But, for some reason, when destroying a session_favorite, line_items are also deleted. Why?
module CurrentFavorite
def set_favorite
if user_signed_in?
set_user_favorite
else
if session[:favorite]
#favorite = Favorite.find(session[:favorite])
else
#favorite = Favorite.create
session[:favorite] = #favorite.id
end
end
end
def set_user_favorite
if session[:favorite]
if current_user.favorite.nil?
#favorite = Favorite.find(session[:favorite])
session[:favorite] = nil
#favorite.update(user: current_user)
else
#block with error
session_favorite = Favorite.find(session[:favorite])
#favorite = Favorite.find_by(user: current_user)
session_favorite.line_items.each do |line_item|
line_item.update(favorite: #favorite)
end
session[:favorite] = nil
session_favorite.destroy
#favorite
end
else
if current_user.favorite.nil?
#favorite = current_user.build_favorite
#favorite.save
else
#favorite = Favorite.find_by(user: current_user)
end
end
end
end
LineItem Update (0.7ms) UPDATE "line_items" SET "favorite_id" = ?, "updated_at" = ? WHERE "line_items"."id" = ? [["favorite_id", 1], ["updated_at", "2020-06-07 05:19:54.653064"], ["id", 13]]
↳ app/models/concerns/current_favorite.rb:31
(12.9ms) commit transaction
↳ app/models/concerns/current_favorite.rb:31
(0.0ms) begin transaction
↳ app/models/concerns/current_favorite.rb:31
Movie Load (0.1ms) SELECT "movies".* FROM "movies" WHERE "movies"."id" = ? LIMIT ? [["id", 2], ["LIMIT", 1]]
↳ app/models/concerns/current_favorite.rb:31
LineItem Update (0.7ms) UPDATE "line_items" SET "favorite_id" = ?, "updated_at" = ? WHERE "line_items"."id" = ? [["favorite_id", 1], ["updated_at", "2020-06-07 05:19:54.674229"], ["id", 14]]
↳ app/models/concerns/current_favorite.rb:31
(3.6ms) commit transaction
↳ app/models/concerns/current_favorite.rb:31
(0.0ms) begin transaction
↳ app/models/concerns/current_favorite.rb:34
LineItem Destroy (0.5ms) DELETE FROM "line_items" WHERE "line_items"."id" = ? [["id", 13]]
↳ app/models/concerns/current_favorite.rb:34
LineItem Destroy (0.1ms) DELETE FROM "line_items" WHERE "line_items"."id" = ? [["id", 14]]
↳ app/models/concerns/current_favorite.rb:34
Favorite Destroy (0.2ms) DELETE FROM "favorites" WHERE "favorites"."id" = ? [["id", 10]]
↳ app/models/concerns/current_favorite.rb:34

Answer 1

session_favorite still has the set of line_items associated with it. For performance reasons, Rails does not automatically reload the line_items before destroying the session_favorite so it doesn't recognize that the line_items are now associated with a different favorite.
To prevent the line_items being destroyed, refresh the association before doing the destroy:
session_favorite.line_items.reload
session_favorite.destroy