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Active Record Associations in Rails

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Destroying Dependent Models

1:27 with Jay McGavren

If you destroy a record that has_many associated records, by default, those associated records will be left in the database. Sometimes these are called "orphaned" records, because their parent record is gone. If you want associated records to be removed when their parent is removed, you can add the dependent: :destroy option to the has_many association in the model class.

If you destroy a record that has_many associated records, by default, those associated records will be left in the database. Sometimes these are called "orphaned" records, because their parent record is gone.

Right now, if we destroy a Movie, for example, Actor instances belonging to that movie will be left in the database.

If you want associated records to be removed when their parent is removed, you can add the dependent: :destroy option to the has_many association in the model class.

class Show < ApplicationRecord
  has_many :actors, as: :production, dependent: :destroy
end

class Movie < ApplicationRecord
  has_many :actors, as: :production, dependent: :destroy
end

In the future, when we destroy any Movie or Show instance, Actor instances belonging to that production will be removed as well.

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    If you destroy a record that has many associated records, by default, 0:00
    those associated records will be left in the database. 0:04
    Sometimes these are called orphaned records because their 0:07
    parent record is gone. 0:10
    So, let's try destroying a movie here. 0:11
    Movie.first.destroy. 0:14
    That gets rid of the movie Fight Club. 0:19
    And now if we pretty print the list of actors, 0:22
    We can see the actors from movie_id: 1 are still present in the database. 0:28
    If you want associated records to be removed when their parent is removed, 0:33
    you can add the dependent destroy option to the Association in the model class. 0:36
    So we can go into our Show model class here, and 0:43
    add dependent: :destroy. 0:46
    And we can copy that and add the same attribute to the, 0:52
    has_many actors association in the Movie class. 0:57
    Okay, let's exit our rails console and rerun it to load our changes. 1:02
    And now let's try destroying a show. 1:06
    Show.first.destroy will delete the Game of Thrones record. 1:08
    If we list all the actors, we'll still see the orphaned 1:14
    actors from the movie we destroyed before, but not the records for the show. 1:19
    And when we destroy movies in the future, their actors will be removed as well. 1:23

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