Explicit aggregate factory functions

[commanded]

Explicit aggregate factory functions

[drozzy]

How will this translate to non-execute version? Or will it just stay the same (which is ok I think)?

[slashdotdash]

@drozzy Good catch, I think that also needs to change, proposal as below.

Current: Command handler receives default %BankAccount{} state

defmodule OpenAccountHandler do
  @behaviour Commanded.Commands.Handler

  def handle(%BankAccount{} = aggregate, %OpenAccount{account_number: account_number, initial_balance: initial_balance}) do
    BankAccount.open_account(aggregate, account_number, initial_balance)
  end
end

Proposal: Command handler receives no state

When there are no persisted events for the aggregate.

defmodule OpenAccountHandler do
  @behaviour Commanded.Commands.Handler

  def handle(%OpenAccount{account_number: account_number, initial_balance: initial_balance}) do
    BankAccount.open_account(account_number, initial_balance)
  end
end

[drozzy]

Wouldn't that need to percolate down to the apply function?

It presently takes a state. Unless you do:

def apply(%AccountOpened{..}) do
   %InitialStateHere{}
end

[slashdotdash]

@drozzy I'm undecided about changing the apply/2 function.

[Freyskeyd]

Is there any update on this issue?

Still undecided? Abandoned ?

[pcarvsilva]

@slashdotdash

I would prefer not using a apply but a create function, since the aggregate does not exists if it is not created.

It does makes more sense to say that a command was processed and created and event and and aggregate, that say that the aggregate already existed with nil fields

It would also help with pattern matching on execute(), if there's no aggregate it should return nil on the execute function and the default call should return {:error, :aggregate_not_created}

[yordis]

Prefer something like new or initial_state; otherwise, it would be confusing. Also, some folks are aligned around https://thinkbeforecoding.com/post/2021/12/17/functional-event-sourcing-decider in terms of naming things to some extent.

Being said, since structs allow you to have default values, I am wondering if this should be a feature.