python - 使用 django channel 保存数据库更改

Question

我希望在 django channel 中制作简单的程序 - 我打开 Websocket，然后监听用户单击按钮或按下任意键。如果发生此类事件，JS 会向 Channels 发送消息，在 Channels 中它可以访问有计数器模型的 db，根据单击或按键来递增它，然后将其发送回层上的组。不幸的是，发生了错误。如果我已经使用了database_sync_to_async，为什么它会调用上下文错误？

我的consumers.py:

from channels.generic.websocket import AsyncWebsocketConsumer
import json
from channels.db import database_sync_to_async
from .models import Licznik
    
    class MyConsumer(AsyncWebsocketConsumer):
        async def connect(self):
            self.room_group_name = 'main_room'
            self.counter = await database_sync_to_async(self.get_counter)()
    
            await (self.channel_layer.group_add)(
                self.room_group_name,
                self.channel_name
            )
            await self.accept()
    
    
       def get_counter(self):
           return Licznik.objects.all()[0]
    
       async def receive(self, text_data):
            if text_data == "klik":
                self.counter.klik +=1
            elif text_data == "klak":
                self.counter.key += 1
            await database_sync_to_async(self.counter.save()) #error here
            klik = self.counter.klik
            klak = self.counter.key
            await (self.channel_layer.group_send)(
                self.room_group_name,
                {
                    'type': 'chat_message',
                    'klik': klik,
                    'klak': klak
                }
            )
    
       async def chat_message(self, event):
            message_klik = event['klik']
            message_klak = event['klak']
            await self.send(text_data=json.dumps({
                'klik': message_klik,
                'klak': message_klak
            }))
    
       async def disconnect(self, close_code):
            await (self.channel_layer.group_discard)(
                self.room_group_name,
                self.channel_name
            )
            await self.close()

错误:

Exception inside application: You cannot call this from an async context - use a thread or sync_to_async.
Traceback (most recent call last):
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/channels/sessions.py", line 183, in __call__
    return await self.inner(receive, self.send)
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/channels/middleware.py", line 41, in coroutine_call
    await inner_instance(receive, send)
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/channels/consumer.py", line 58, in __call__
    await await_many_dispatch(
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/channels/utils.py", line 51, in await_many_dispatch
    await dispatch(result)
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/channels/consumer.py", line 73, in dispatch
    await handler(message)
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/channels/generic/websocket.py", line 196, in websocket_receive
    await self.receive(text_data=message["text"])
  File "/Users/dottore/PycharmProjects/klikator/klikator/klikacz/consumers.py", line 26, in receive
    await database_sync_to_async(self.counter.save())
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/django/db/models/base.py", line 753, in save
    self.save_base(using=using, force_insert=force_insert,
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/django/db/models/base.py", line 790, in save_base
    updated = self._save_table(
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/django/db/models/base.py", line 872, in _save_table
    updated = self._do_update(base_qs, using, pk_val, values, update_fields,
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/django/db/models/base.py", line 926, in _do_update
    return filtered._update(values) > 0
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/django/db/models/query.py", line 803, in _update
    return query.get_compiler(self.db).execute_sql(CURSOR)
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1522, in execute_sql
    cursor = super().execute_sql(result_type)
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1154, in execute_sql
    cursor = self.connection.cursor()
  File "/Users/dottore/PycharmProjects/klikator/venv/lib/python3.8/site-packages/django/utils/asyncio.py", line 24, in inner
    raise SynchronousOnlyOperation(message)
django.core.exceptions.SynchronousOnlyOperation: You cannot call this from an async context - use a thread or sync_to_async.

Answer 1

您应该调用 database_sync_to_async方法，而不是直接保存方法:

async def receive(self, text_data):
        ...
        await database_sync_to_async<b>(self.counter.save)()</b>
        ...