Update asgi templates

[sinisaos]

Related to #1242

[dantownsend]

This looks good - thank you. I'll try and give it a go tomorrow 👍

[sinisaos]

Great. Thanks.

[dantownsend]

This looks good to me.

My only thoughts were:

1. Whether we should be returning a 404 if a PUT tries to update a resource which doesn't exist (some people wouldn't treat this as an error). But this is the behaviour we already had in the previous templates, so lets leave it.
2. We use Task._meta.primary_key. An alternative is to do Task.id, but then to add the following to the Task table definition:

class Task(Table):
    """
    An example table.
    """
    id: Serial
    name = Varchar()
    completed = Boolean(default=False)

[sinisaos]

• Whether we should be returning a 404 if a PUT tries to update a resource which doesn't exist (some people wouldn't treat this as an error). But this is the behaviour we already had in the previous templates, so lets leave it.

I think that's the right behavior and using a callback method is really handy in those cases.

• We use Task._meta.primary_key. An alternative is to do Task.id, but then to add the following to the Task table definition:

Usually when I'm not using a custom primary key, I let Piccolo to automatically create the primary key column. In that case Task._meta.primary_key is a convenient way to satisfy a tool like mypy. I think we should leave this, but if you want, I can change it.

[dantownsend]

Looks good, thanks!