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Does Active Record's dependent: :destroy also delete the database records?

e.g. dependent: :delete

Natus Drew
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3 Answers3

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Yes, both will delete the database records but doing it in a different way.

You can check the answer for this question here:

Rails :dependent => :destroy VS :dependent => :delete_all

Basically dependent: :delete will execute the delete for the dependent records directly on the database without executing any activerecod validations or callbacks.

While dependent: :destroy will instantiate all the dependent records and execute a :destroy for each object (executing validations and callbacks).

Daniel Fernández Pescetto
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  • Thanks. That's the exact answer I was looking for. I wanted to know if I can just use :destroy to remove the objects and database records. – Natus Drew May 13 '20 at 21:55
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The :destroy option loads each dependent record from the database and calls the destroy method of that object. The :delete option deletes each record directly from the database without calling destroy or any callbacks.


Documentation for each association type can be found here:

belongs_to: https://guides.rubyonrails.org/association_basics.html#options-for-belongs-to-dependent

has_one: https://guides.rubyonrails.org/association_basics.html#options-for-has-one-dependent

has_many: https://guides.rubyonrails.org/association_basics.html#dependent

Ken Hill
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  • I'm not sure why one would use :delete when that leaves the objects instantiated? Can't that lead to errors where code is operating on objects that don't exist in the database? – Natus Drew May 13 '20 at 21:57
  • Delete sends sql to the database, it won't instantiate anything. Destroy will instantiate and then destroy associated objects. Any subsequent attempt to access an association that has been destroyed will return an empty collection or nil, depending on the type of association. Any instances of destroyed objects that remain will produce an error when attempting to read/write from the database. – Ken Hill May 15 '20 at 00:33
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What does Delete do?

Delete Documentation In basic terms, using delete removes the row in the database using a primary key matching the id argument, using a SQL DELETE statement, and returns the number of rows deleted. You can delete multiple rows at once by passing an Array of ids. But when calling delete, that’s it. Nothing else behind the scenes happens.

What does Destroy do?

Destroy Documentation As you can see, using destroy also removes a given id (or ids) from a table. However, an object is instantiated first, therefore all callbacks and filters are fired off before the object is “deleted”. Because of the extra callbacks and validations performed before the object is “deleted”, this method is less efficient than ActiveRecord#delete, but it allows cleanup methods and other actions to be run. Essentially, this finds the given id, creates a new object from the attributes, and then calls destroy on it (performing any dependencies and callbacks).

Giridharan
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