Async connection created callback

[alicederyn]

I need to issue a set of SQL commands at the start of each connection, e.g. to set up the search path. Currently it looks like this can only be done by subclassing Database and completely reimplementing its connection method to return a subclass of Connection that overrides __aenter__. Would it be acceptable to add something akin to Django's connection_created signal? Syntax might look like

@db.connection_created
async def set_search_path(connection):
  await connection.execute("set search_path = my_schema")

[alicederyn]

For reference, here is my subclass implementation:

from databases.core import Connection as BasicConnection, Database as BasicDatabase

class Connection(BasicConnection):
    def __init__(self, backend, init_fns) -> None:
        super().__init__(backend)
        self.init_fns = init_fns

    async def __aenter__(self):
        c = await super().__aenter__()
        for init_fn in self.init_fns:
            await init_fn(c)
        return c


class Database(BasicDatabase):
    """Adds a connection_created decorator to encode/databases."""

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self._init_fns = []

    def connection_created(self, async_callback_fn):
        self._init_fns.append(async_callback_fn)

    def connection(self):
        """This method copies the underlying implementation wholesale. Calling it with super is
        unfortunately not an option as it has a hard-coded reference to its own Connection
        implementation."""
        if self._global_connection is not None:
            return self._global_connection

        try:
            return self._connection_context.get()
        except LookupError:
            connection = Connection(self._backend, self._init_fns)
            self._connection_context.set(connection)
            return connection