1.19.0

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

For example, if we have this table:

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:

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.