How to add and remove elements from the list in Ash atomic action?

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1

How one would add or remove elements from an array in an atomic action. Tried using fragments but kept getting errors.

  Map.put(
          changes,
          :state_history,
          expr(fragment("array_prepend(?, coalesce(?, '{}'))", ^new_state, ^ref(:state_history)))
        )

      IO.inspect(changes)
      {:atomic, changes, checks}
  • ** (KeyError) key :atomic_validations not found in: {:not_atomic,
    “Cannot atomically update AThing.state_history: Cannot cast a non-literal list atomically”}

I am going a bit blindly, any input appreciated.

2

I guess you have tried this?

change atomic_update(:score, fragment("array_prepend(?, coalesce(?, '{}'))", ^new_state, ^ref(:state_history)))

https://hexdocs.pm/ash/update-actions.html#fully-atomic-updates

3

Since I am in the context of atomic/3 callback I cannot use this directly.
Traced the thing back, and got this:

Ash.Resource.Change.Atomic.atomic(
        changeset,
        [
          attribute: :history,
          expr:
            expr(
              fragment("array_prepend(?, coalesce(?, '{}'))", ^new_state, ^ref(:state_history))
            )
        ],
        context
      )

Yet to test it.

4 
Map.put(
          changes,
          :state_history,
          {:atomic, expr(fragment("array_prepend(?, coalesce(?, '{}'))", ^new_state, ^ref(:state_history)))}
        )

      IO.inspect(changes)
      {:atomic, changes, checks}

If you want to override the underlying atomic type casting (which in this case isn’t possible or necessary), you can return it in that {:atomic, ...} tuple.