I'm thinking that for our purposes:
1. Because several Django projects need a migration from sync to async
which requires time and resources, sync engines can specify a new key
called ASYNC_DATABASE_ALIAS whose value is a string that is a database
alias in the DATABASES dict. The purpose of this is two-fold: A) ease
Django project migrations to async and B) allow for testing on Django
internal test suite and third-party packages. This also helps with
backwards compatibility for the templating system such that when we
call Model.objects.acreate, because of that a prefix, we can implicitly use
the async engine.
2. Projects that start off as async or have their default engine as
async need an option called SYNC_DATABASE_ALIAS that is exactly like
the ASYNC_DATABASE_ALIAS option. The purpose for this is to fill in the gap
of DEP 9 by having a migration and schema engine changer since async
engines aren't supposed to. In the database wrapper, we would grab the sync
database's database wrapper's Schema class.
It'll look like this:
DATABASES = { 'default': { 'ENGINE': 'django.db.backends.aiosqlite',
'SYNC_DATABASE_ALIAS': 'sync' }, 'sync': { 'ENGINE':
'django.db.backends.sqlite3', }, }
or
DATABASES = { 'default': { 'ENGINE': 'django.db.backends.sqlite3',
'ASYNC_DATABASE_ALIAS': 'async' }, 'async': { 'ENGINE':
'django.db.backends.aiosqlite', }, }
I'm not sure if either of these options are possible due to sqlite being
tested in memory though.
On Monday, January 31, 2022 at 6:48:13 PM UTC-5 Adam Johnson wrote:
> Hi Andrew,
>
> I'm afraid I don't know much about async, but I can point you at some
> recent changes. Andrew Godwin created a PR with the draft of the async ORM
> API. Carlton recently asked for tests:
> https://twitter.com/carltongibson/status/1486281689265545221 . Perhaps
> check out those PR's and see if you can contribute further?
>
> Adam
>
> On Sat, Jan 29, 2022 at 1:42 AM Andrew Wang <acwang...@gmail.com> wrote:
>
>> Hi, I'm intrigued in helping develop the async ORM engines (link to
>> random PR <https://github.com/django/django/pull/15357> with aiosqlite
>> and base async engine). The biggest road block is having test cases for
>> async engines only; for instance, introspection/test_async.py can't run
>> because the test suite needs to first migrate using a sync engine as the
>> default database connection then switch the default alias to using an async
>> engine; additionally, for most of the test suite, it uses the sync engine.
>> The current methods I'm thinking of:
>>
>> 1. Each async engine would get its own CI worker. I think it's a waste of
>> resources and because it wouldn't help Django users who also need to write
>> test cases with both an async and sync (for migrations) engine.
>> 2. Async and sync engines for the same database are run at the same time.
>> Every async engine requires a parallel sync engine, an alias to be
>> specified in the engine's DATABASES options. This way, while testing,
>> migrations can be performed with a designated sync engine. This is great
>> for the end user who may be async-centric; this doesn't really resolve the
>> current problem. Most of the Django test suite is designed for synchronous
>> db engines, so the default alias database engine will switch around a bunch
>> of times.
>> 3. Implement a test decorator that switches the default alias connection.
>>
>> Lemme know if that's confusing.
>>
>> Thanks,
>> Andrew
>>
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