Implementing Custom Tasks
=========================

Introduction
------------

In this second tutorial we are going to implement our own task, and
use serialization and deserialization to store and restore it.

If you haven't already, you should complete the first
:doc:`../tutorial/index`.
We are also assuming that you are familiar with the :doc:`../basics`.

Implementing the custom task
----------------------------

The first step is to create a :class:`SpiffWorkflow.specs.TaskSpec` that
fires the rocket::

    from SpiffWorkflow.specs import Simple

    class NuclearStrike(Simple):
        def _on_complete_hook(self, my_task):
            print("Rocket sent!")

Save this file as ``strike.py``.

Now, before we are ready to define the workflow using XML or JSON, we will
also have extend the serializer to let SpiffWorkflow know how to represent
your NuclearStrike first.

Preparing a serializer
----------------------

Before we can use JSON to specify a workflow, we first need to teach
SpiffWorkflow what our custom `NuclearChoice` looks like in JSON.
We do this by extending the
:mod:`SpiffWorkflow.serializer.json.JSONSerializer`.

.. literalinclude:: serializer.py

We save the serializer as ``serializer.py``.
We also need to update ``strike.py`` as follows:

We also implement the deserializer:

.. literalinclude:: strike.py

That is all! You are now ready to create the specification from JSON.

Creating a workflow specification (using JSON)
----------------------------------------------

Now we can use the NuclearStrike in the workflow specification in JSON.
Note that this specification is the same as in our first tutorial,
except that it references our class `strike.NuclearStrike`.

.. literalinclude:: nuclear.json

Using the custom serializer and task
------------------------------------

Here we use our brand new serializer in practice:

.. literalinclude:: start.py