Piccolo

------

Fixed a bug with the ``get_m2m`` method, which would raise a ``ValueError``
when no objects were found. It now handles this gracefully and returns an empty
list instead. Thanks to nVitius for this fix.

Improved the ASGI templates (including a fix for the latest Litestar version).
Thanks to sinisaos for this.

-------------------------------------------------------------------------------

------

Added support for row locking (i.e. ``SELECT ... FOR UPDATE``).

For example, if we have this table:

.. code-block:: python

class Concert(Table):
name = Varchar()
tickets_available = Integer()

And we want to make sure that ``tickets_available`` never goes below 0, we can
do the following:

.. code-block:: python

async def book_tickets(ticket_count: int):
async with Concert._meta.db.transaction():
concert = await Concert.objects().where(
Concert.name == "Awesome Concert"
).first().lock_rows()

if concert.tickets_available >= ticket_count:
await concert.update_self({
Concert.tickets_available: Concert.tickets_available - ticket_count
})
else:
raise ValueError("Not enough tickets are available!")

This means that when multiple transactions are running at the same time, it
isn't possible to book more tickets than are available.

Thanks to dkopitsa for adding this feature.

-------------------------------------------------------------------------------

------

``update_self``
~~~~~~~~~~~~~~~

Added the ``update_self`` method, which is an alternative to the ``save``
method. Here's an example where it's useful:

.. code-block:: python

If we have a band object:
>>> band = await Band.objects().get(name="Pythonistas")
>>> band.popularity
1000

We can increment the popularity, based on the current value in the
database:
>>> await band.update_self({
... Band.popularity: Band.popularity + 1
... })

The new value is set on the object:
>>> band.popularity
1001

It's safer than using the `save` method, because the popularity value on
the object might be out of date with what's in the database:
band.popularity += 1
await band.save()

Thanks to trondhindenes for suggesting this feature.

Batch raw queries
~~~~~~~~~~~~~~~~~

The ``batch`` method can now be used with ``raw`` queries. For example:

.. code-block:: python

async with await MyTable.raw("SELECT * FROM my_table").batch() as batch:
async for _batch in batch:
print(_batch)

This is useful when you expect a raw query to return a lot of data.

Thanks to devsarvesh92 for suggesting this feature.

-------------------------------------------------------------------------------

------

Fixed a bug with migrations, where altering a column type from ``Integer`` to
``Float`` could fail. Thanks to kurtportelli for reporting this issue.

-------------------------------------------------------------------------------

------

Each migration is automatically wrapped in a transaction - this can now be
disabled using the ``wrap_in_transaction`` argument:

.. code-block:: python

manager = MigrationManager(
wrap_in_transaction=False,
...
)

This is useful when writing a manual migration, and you want to manage all of
the transaction logic yourself (or want multiple transactions).

``granian`` is now a supported server in the ASGI templates. Thanks to
sinisaos for this.

-------------------------------------------------------------------------------

------

Added custom async ``TestCase`` subclasses, to help with testing.

For example ``AsyncTransactionTest``, which wraps each test in a transaction
automatically:

.. code-block:: python

class TestBandEndpoint(AsyncTransactionTest):

async def test_band_response(self):
"""
Make sure the endpoint returns a 200.
"""
This data automatically gets removed from the database when the
test finishes:
band = Band({Band.name: "Pythonistas"})
await band.save()

Using an API testing client, like httpx:
response = await client.get(f"/bands/{band.id}/")
self.assertEqual(response.status_code, 200)

And ``AsyncTableTest``, which automatically creates and drops tables:

.. code-block:: python

class TestBand(AsyncTableTest):

These tables automatically get created and dropped:
tables = [Band]

async def test_band(self):
...

-------------------------------------------------------------------------------