Migrating Guide
===============

Google's protocolbuffers
------------------------

betterproto has a mostly 1 to 1 drop in replacement for Google's protocolbuffers (after
regenerating your protobufs of course) although there are some minor differences.

.. note::

    betterproto implements the same basic methods including:

        - :meth:`betterproto.Message.FromString`
        - :meth:`betterproto.Message.SerializeToString`

    for compatibility purposes, however it is important to note that these are
    effectively aliases for :meth:`betterproto.Message.parse` and
    :meth:`betterproto.Message.__bytes__` respectively.


Determining if a message was sent
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sometimes it is useful to be able to determine whether a message has been sent on
the wire. This is how the Google wrapper types work to let you know whether a value is
unset (set as the default/zero value), or set as something else, for example.

Use ``betterproto.serialized_on_wire(message)`` to determine if it was sent. This is
a little bit different from the official Google generated Python code, and it lives
outside the generated ``Message`` class to prevent name clashes. Note that it only
supports Proto 3 and thus can only be used to check if ``Message`` fields are set.
You cannot check if a scalar was sent on the wire.

.. code-block:: python

    # Old way (official Google Protobuf package)
    >>> mymessage.HasField('myfield')
    True

    # New way (this project)
    >>> betterproto.serialized_on_wire(mymessage.myfield)
    True


One-of Support
~~~~~~~~~~~~~~

Protobuf supports grouping fields in a oneof clause. Only one of the fields in the group
may be set at a given time. For example, given the proto:

.. code-block:: proto

    syntax = "proto3";

    message Test {
      oneof foo {
        bool on = 1;
        int32 count = 2;
        string name = 3;
      }
    }

You can use ``betterproto.which_one_of(message, group_name)`` to determine which of the
fields was set. It returns a tuple of the field name and value, or a blank string and
``None`` if unset. Again this is a little different than the official Google code
generator:

.. code-block:: python

    # Old way (official Google protobuf package)
    >>> message.WhichOneof("group")
    "foo"

    # New way (this project)
    >>> betterproto.which_one_of(message, "group")
    ("foo", "foo's value")


Well-Known Google Types
~~~~~~~~~~~~~~~~~~~~~~~

Google provides several well-known message types like a timestamp, duration, and several
wrappers used to provide optional zero value support. Each of these has a special JSON
representation and is handled a little differently from normal messages. The Python
mapping for these is as follows:

+-------------------------------+-----------------------------------------------+--------------------------+
| ``Google Message``            | ``Python Type``                               | ``Default``              |
+===============================+===============================================+==========================+
| ``google.protobuf.duration``  | :class:`datetime.timedelta`                   | ``0``                    |
+-------------------------------+-----------------------------------------------+--------------------------+
| ``google.protobuf.timestamp`` | ``Timezone-aware`` :class:`datetime.datetime` | ``1970-01-01T00:00:00Z`` |
+-------------------------------+-----------------------------------------------+--------------------------+
| ``google.protobuf.*Value``    | ``Optional[...]``/``None``                    | ``None``                 |
+-------------------------------+-----------------------------------------------+--------------------------+
| ``google.protobuf.*``         | ``betterproto.lib.google.protobuf.*``         | ``None``                 |
+-------------------------------+-----------------------------------------------+--------------------------+


For the wrapper types, the Python type corresponds to the wrapped type, e.g.
``google.protobuf.BoolValue`` becomes ``Optional[bool]`` while
``google.protobuf.Int32Value`` becomes ``Optional[int]``. All of the optional values
default to None, so don't forget to check for that possible state.

Given:

.. code-block:: proto

    syntax = "proto3";

    import "google/protobuf/duration.proto";
    import "google/protobuf/timestamp.proto";
    import "google/protobuf/wrappers.proto";

    message Test {
      google.protobuf.BoolValue maybe = 1;
      google.protobuf.Timestamp ts = 2;
      google.protobuf.Duration duration = 3;
    }

You can use it as such:

.. code-block:: python

    >>> t = Test().from_dict({"maybe": True, "ts": "2019-01-01T12:00:00Z", "duration": "1.200s"})
    >>> t
    Test(maybe=True, ts=datetime.datetime(2019, 1, 1, 12, 0, tzinfo=datetime.timezone.utc), duration=datetime.timedelta(seconds=1, microseconds=200000))

    >>> t.ts - t.duration
    datetime.datetime(2019, 1, 1, 11, 59, 58, 800000, tzinfo=datetime.timezone.utc)

    >>> t.ts.isoformat()
    '2019-01-01T12:00:00+00:00'

    >>> t.maybe = None
    >>> t.to_dict()
    {'ts': '2019-01-01T12:00:00Z', 'duration': '1.200s'}


[1.2.5] to [2.0.0b1]
--------------------

Updated package structures
~~~~~~~~~~~~~~~~~~~~~~~~~~

Generated code now strictly follows the *package structure* of the ``.proto`` files.
Consequently ``.proto`` files without a package will be combined in a single
``__init__.py`` file. To avoid overwriting existing ``__init__.py`` files, its best
to compile into a dedicated subdirectory.

Upgrading:

- Remove your previously compiled ``.py`` files.
- Create a new *empty* directory, e.g. ``generated`` or ``lib/generated/proto`` etc.
- Regenerate your python files into this directory
- Update import statements, e.g. ``import ExampleMessage from generated``
