значение по умолчанию не работает для sqlalchemy.Column

Question

Я пытаюсь использовать aiomysql + sqlalchemy в соответствии с aiomysql.sa , но проблема возникает при использовании параметра по умолчанию.Ниже все, что я написал.

import asyncio
import sqlalchemy as sa
from aiomysql.sa import create_engine
import time
import uuid

def next_id():
    return '%015d%s000' % (int(time.time() * 1000), uuid.uuid4().hex)

metadata = sa.MetaData()

Test = sa.Table('test', metadata,
            sa.Column('id', sa.String(50), default=next_id, primary_key=True),
            sa.Column('name', sa.String('50')),
            sa.Column('created_at', sa.Float, default=time.time))

async def init_engine(loop):
    print('create engine to connect sql...')
    global __engine
    __engine = await create_engine(
            host='localhost',
            port=3306,
            user='zqy',
            password='123456',
            db='zqyblog',
            loop=loop)

async def test(loop):
    async with __engine.acquire() as conn:
        trans = await conn.begin()
        insr = Test.insert().values(name="test")
        print("SQL: %r" % insr.compile().params)
        await conn.execute(insr)
        await trans.commit()

loop = asyncio.get_event_loop()
loop.run_until_complete(init_engine(loop))
loop.run_until_complete(test(loop))

И я попал под журнал:

create engine to connect sql...
SQL: {'id': None, 'name': 'test', 'created_at': None}
Traceback (most recent call last):
  File "db_simple.py", line 38, in test
    await conn.execute(insr)
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\aiomysql\sa\connection.py", line 173, in _execute
    await cursor.execute(str(compiled), post_processed_params)
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\aiomysql\cursors.py", line 239, in execute
    await self._query(query)
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\aiomysql\cursors.py", line 457, in _query
    await conn.query(q)
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\aiomysql\connection.py", line 428, in query
    await self._read_query_result(unbuffered=unbuffered)
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\aiomysql\connection.py", line 622, in _read_query_result
    await result.read()
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\aiomysql\connection.py", line 1105, in read
    first_packet = await self.connection._read_packet()
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\aiomysql\connection.py", line 593, in _read_packet
    packet.check_error()
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\pymysql\protocol.py", line 220, in check_error
    err.raise_mysql_exception(self._data)
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\pymysql\err.py", line 109, in raise_mysql_exception
    raise errorclass(errno, errval)
pymysql.err.IntegrityError: (1048, "Column 'id' cannot be null")

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "db_simple.py", line 44, in <module>
    loop.run_until_complete(test(loop))
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\asyncio\base_events.py", line 584, in run_until_complete
    return future.result()
  File "db_simple.py", line 39, in test
    await trans.commit()
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\aiomysql\utils.py", line 103, in __aexit__
    await self._pool.release(self._conn)
  File "<my\local\path>\anaconda3\envs\python-webapp\lib\site-packages\aiomysql\sa\engine.py", line 137, in release
    raise InvalidRequestError("Cannot release a connection with "
aiomysql.sa.exc.InvalidRequestError: Cannot release a connection with not finished transaction

Как сказано во второй строке в этом журнале, значение id равно Нет Странно, что я установил default = next_id при определении столбца.У кого-нибудь есть идеи?Большое спасибо.

• mysql 8.05
• python 3.7.2
• sqlalchemy 1.2.18
• aiomysql 0.0.20