delete_all vs destroy_all?

I am looking for the best approach to delete records from a table. For instance, I have a user whose user ID is across many tables. I want to delete this user and every record that has his ID in all tables.

u = User.find_by_name('JohnBoy')
u.usage_indexes.destroy_all
u.sources.destroy_all
u.user_stats.destroy_all
u.delete

This works and removes all references of the user from all tables, but I heard that `destroy_all` was very process heavy, so I tried `delete_all`. It only removes the user from his own user table and the `id` from all the other tables are made null, but leaves the records intact in them. Can someone share what the correct process is for performing a task like this?

I see that `destroy_all` calls the `destroy` function on all associated objects but I just want to confirm the correct approach.

delete_all is a single SQL DELETE statement and nothing more. destroy_all calls destroy() on all matching results of :conditions (if you have one) which could be at least NUM_OF_RESULTS SQL statements.

If you have to do something drastic such as destroy_all() on large dataset, I would probably not do it from the app and handle it manually with care. If the dataset is small enough, you wouldn't hurt as much.

To avoid the fact that <code>destroy_all</code> instantiates all the records and destroys them one at a time, you can use it directly from the model class.

So instead of :

u = User.find_by_name('JohnBoy')
u.usage_indexes.destroy_all

You can do :

u = User.find_by_name('JohnBoy')
UsageIndex.destroy_all "user_id = #{u.id}"

The result is one query to destroy all the associated records

You are right. If you want to delete the User and all associated objects -> `destroy_all`
However, if you just want to delete the User without suppressing all associated objects -> `delete_all`

According to this post :

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- `destroy` / `destroy_all`: The associated objects are destroyed alongside this object by calling their destroy method
- `delete` / `delete_all`: All associated objects are destroyed immediately without calling their :destroy method

I’ve made a [small gem](

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) that can alleviate the need to manually delete associated records in some circumstances.

>This gem adds a new option for ActiveRecord associations:
>
>dependent: :delete_recursively
>
>When you destroy a record, all records that are associated using this option will be deleted recursively (i.e. across models), without instantiating any of them.
>
>Note that, just like dependent: :delete or dependent: :delete_all, this new option does not trigger the around/before/after_destroy callbacks of the dependent records.
>
>However, it is possible to have dependent: :destroy associations anywhere within a chain of models that are otherwise associated with dependent: :delete_recursively. The :destroy option will work normally anywhere up or down the line, instantiating and destroying all relevant records and thus also triggering their callbacks.