How do I destroy all records?

Elixir Framework Forums Ash Forum
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1

Hello all,

Is there an idiomatic way to destroy all records in the table with Ash Framework, similar to read_all()?
Or maybe some escape hatch to Ecto?

I tried to do it with manual action, but it requires changeset.
The only way I could think of is to do it with generic action, something like

    action :destroy_all, :string do
      argument :dummy, :string, allow_nil?: true

      run(fn _input, _context ->
        read_all!()
        |> Enum.map(&destroy!(&1))

        {:ok, []}
      end)
    end

But that’s suboptimal, to say the least.

EDIT: clarification that the question is Ash related

2

Have a look at the docs: Repo.delete_all/2

EDIT: re-read the question and it seems it’s more about the Ash way of doing it. But the docs above is how to do it with raw Ecto, just need to figure out how to call it from Ash. Maybe: Manual Actions — ash v2.15.19

3

Yeah I am also not super sure about how to do this in Ash, but as a minor database note TRUNCATE is the ideal way to delete all rows in a table. delete_all has to essentially write an update for every row, marking it as deleted, where as TRUNCATE basically just deletes the file associated with the table data.

4

I would agree that TRUNCATE would be the first choice if all conditions allow… and in many basic scenarios you’ll be fine; but one needs to use TRUNCATE with some care in more complex scenarios. (Assuming PostgreSQL)

  • There are special considerations if the table is used in other table foreign key references.

  • If you have ON DELETE triggers, they will not fire.

  • TRUNCATE is not fully MVCC safe in relation to certain concurrent transactions.

and there are one or two other more subtle issues as well (PostgreSQL: Documentation: 16: TRUNCATE).

Because of the special nature of TRUNCATE and the efficiency it tries to bring to mass delete operations, there can be similar issues in other vendor’s databases as well. For example, in PostgreSQL, while fully not MVCC safe, you can roll back a TRUNCATE operation, but in Oracle you cannot.

So I would advise anyone needing to delete all the data in a table to TRUNCATE if they can, but it’s one of those commands that you really need to understand and use with care.

3 Likes
5

Ash doesn’t have a bulk delete or truncate, so you’d use ecto directly to either delete everything with TRUNCATE or Repo.delete_all

6

Thank you all for your help!

So just to close the case, I ended up using following generic action:

  actions do
    defaults [:create, :read, :update, :destroy]

    action :destroy_all, :term do
      run(fn _, _ ->
        case __MODULE__
             |> MyApp.Repo.to_ecto()
             |> MyApp.Repo.delete_all() do
          {n, result} when is_integer(n) -> {:ok, result}
          error -> {:error, error}
        end
      end)
    end
  end

And that gives me MyApp.Api.Resource.destroy_all()

1 Like