The Commanded.Aggregates.AggregateLifespan behaviour is used to control an aggregate lifespan.

By default an aggregate instance process will run indefinitely once started. You can control this by implementing the Commanded.Aggregates.AggregateLifespan behaviour in a module and configuring it in your router.

After a command successfully executes, and creates at least one domain event, the after_event/1 function is called passing the last created event. The returned inactivity timeout value is used to shutdown the aggregate process if no other messages are received.

Supported return values

• Non-negative integer - specify an inactivity timeout, in millisconds.
• :infinity - prevent the aggregate instance from shutting down.
• :hibernate - send the process into hibernation.
• :stop - immediately shutdown the aggregate process.

Hibernation

A hibernated process will continue its loop once a message is in its message queue. Hibernating an aggregate causes garbage collection and minimises the memory used by the process. Hibernating should not be used aggressively as too much time could be spent garbage collecting.

Example

Define a module that implements the Commanded.Aggregates.AggregateLifespan behaviour:

defmodule BankAccountLifespan do
  @behaviour Commanded.Aggregates.AggregateLifespan

  def after_event(%BankAccountOpened{}), do: :infinity
  def after_event(%MoneyDeposited{}), do: 60_000
  def after_event(%BankAccountClosed{}), do: :stop
end

Then specify the module as the lifespan option when registering the applicable commands in your router:

defmodule BankRouter do
  use Commanded.Commands.Router

  dispatch [OpenAccount, CloseAccount],
    to: BankAccount,
    lifespan: BankAccountLifespan,
    identity: :account_number
end