Lifecycle callbacks

[sitch]

Would be nice to use multiple callbacks in order to support things like Ecto.Multi. So instead of just having a :callback which needs to call :validate_state_transition which expects an Ecto.Changeset, you have :before_transition and an :after_transition.

This allows you to do

  use EctoStateMachine,
    states: [:initial, :confirmed],
    events: [
      [
        name:     :confirm,
        from:     [:inital],
        to:       :confirmed,
        before_transition: fn(model, _params) -> Ecto.Changeset.change(model, expired_at: Ecto.DateTime.utc()),
        after_transition: fn(changeset, params) do
          Multi.new
          |> Multi.update(changeset)
          |> Multi.insert(TBD.changeset(%TBD{}, params)
        end
      ]
    ]

Now you can call User.confirm(params) and the params supplied will get applied to the transition functions.