The Chronik.Aggregate is the base for all aggregates in Chronik.

The module that uses Chronik.Aggregate module can be configured with a number of options:

• shutdown_timeout indicates Chronik to shutdown the aggregate GenServer after a number of milliseconds. Defualt value is 15 minutes.
• snapshot_every indicates that a snapshot must be done on the Store every snapshot_every domain events processed. Default value is 100. This configuration is looked up in the :chronik app under the given module.

Example:

defmodule DomainEvents do
  defmodule CounterCreated do
    defstruct [:id]
  end

  defmodule CounterIncremented do
    defstruct [:id, :increment]
  end
end

defmodule Counter do
  use Chronik.Aggregate

  alias DomainEvents.CounterCreated
  alias DomainEvents.CounterIncremented

  defstruct [:id]

  def handle_command({:create, id}) do
    Counter.call(id,
      fn state ->
        execute(state, &validate_create(&1, id))
      end)
  end
  def handle_command({:increment, id, increment}) do
    Counter.call(id,
      fn state ->
        execute(state, &validate_increment(&1, id, increment))
      end)
  end

  def handle_event(%CounterCreated{id: id}, nil) do
    %Counter{id: id}
  end

  def handle_event(%CounterIncremented{}, %Counter{} = state) do
    state
  end

  defp validate_create(nil, id) do
    %Counter{id: id}
  end
  defp validate_create(_state, _id) do
    raise "cannot create counter"
  end

  defp validate_increment(%Counter{}, id, increment) do
    %CounterIncremented{id: id, increment: increment}
  end
  defp validate_increment(_state, _id, _increment) do
    raise "cannot increment counter"
  end
end

The application code must implement the handle_command and handle_event callback.

The Chronik.Macros provides helper macros to define events and commands.