TaskLocals doesn't share parent's Task context with child one's

[mullakhmetov]

Peewee related task context such as connection or transaction_depth is stored in TaskLocals object with id(asyncio.current_task()) acts like a key.

This behavior causes painful problem with asyncio.gather inside transaction block:

from models import TestModel

class MyTest(BaseTest):
    async def create_obj(self):
        return await self.objects.create(TestModel)

    async def get_obj(self, obj_id):
        await self.objects.get(TestModel, TestModel.id == obj_id)

    async def indirect_get_obj(self, obj_id):
        await self.get_obj(obj_id)

    async def ensured_get_obj(self, obj_id):
        await asyncio.ensure_future(self.get_obj(obj_id))
    
    async def test_transaction(self):
        async with self.objects.atomic():
            obj_id = (await self.create_obj()).id

            await self.objects.get(TestModel, TestModel.id == obj_id)
            await self.get_obj(obj_id)
            await self.indirect_get_obj(obj_id)

            with self.assertRaises(TestModel.DoesNotExist):
                # new tasks loose context and spawn new db connections
                await self.ensured_get_obj(obj_id)
                await asyncio.gather(self.get_obj(obj_id))