通过 URL 参数进行数据库路由

Question

我正在开发具有多个数据库的 Django 项目。在应用程序中，我需要根据用户的请求将数据库连接从 Development-Database 切换到 Test-DB 或 Production-DB。（数据库架构已设置且不可更改！）

我也在这里用这个旧指南试了运气 不起作用。在数据库路由器中，我无法访问 threading.locals。

我也尝试过设置自定义数据库路由器。通过会话变量，我尝试设置连接字符串。要读取 dbRouter 中的用户会话，我需要确切的会话密钥，否则我必须循环抛出所有会话。

object.using('DB_CONNECTION) 的方式是不可接受的解决方案......对于许多依赖项。我想为登录用户全局设置连接，而不为每个模型功能提供数据库连接......

请给我一些如何解决这个问题的意见。

我应该能够根据会话值在数据库路由器中返回 dbConnection...

def db_for_read|write|*():
   from django.contrib.sessions.backends.db import SessionStore
   session = SessionStore(session_key='WhyINeedHereAKey_SessionKeyCouldBeUserId')
   return session['app.dbConnection']

更新 1： 感谢 @victorT 的贡献。我只是用给定的例子尝试过。还是没有达到目标……

这是我尝试过的。可能你会看到一个配置错误。

Django Version:     2.1.4
Python Version:     3.6.3
Exception Value:    (1146, "Table 'app.myModel' doesn't exist")

.app/views/myView.py

from ..models import myModel
from ..thread_local import thread_local

class myView:
    @thread_local(DB_FOR_READ_OVERRIDE='MY_DATABASE')
    def get_queryset(self, *args, **kwargs):
        return myModel.objects.get_queryset()

.app/myRouter.py

from .thread_local import get_thread_local

class myRouter:
    def db_for_read(self, model, **hints):
        myDbCon = get_thread_local('DB_FOR_READ_OVERRIDE', 'default')
        print('Returning myDbCon:', myDbCon)
        return myDbCon

.app/thread_local.py

import threading
from functools import wraps


threadlocal = threading.local()


class thread_local(object):
    def __init__(self, **kwargs):
        self.options = kwargs

    def __enter__(self):
        for attr, value in self.options.items():
            print(attr, value)
            setattr(threadlocal, attr, value)

    def __exit__(self, exc_type, exc_value, traceback):
        for attr in self.options.keys():
            setattr(threadlocal, attr, None)

    def __call__(self, test_func):

        @wraps(test_func)
        def inner(*args, **kwargs):
            # the thread_local class is also a context manager
            # which means it will call __enter__ and __exit__
            with self:
                return test_func(*args, **kwargs)

        return inner

def get_thread_local(attr, default=None):
    """ use this method from lower in the stack to get the value """
    return getattr(threadlocal, attr, default)

这是输出：

Returning myDbCon: default              
DEBUG (0.000) None; args=None
DEBUG (0.000) None; args=None
DEBUG (0.000) None; args=('2019-05-14 06:13:39.477467', '4agimu6ctbwgykvu31tmdvuzr5u94tgk')
DEBUG (0.001) None; args=(1,)
DB_FOR_READ_OVERRIDE MY_DATABASE        # The local_router seems to get the given db Name,
Returning myDbCon: None                 # But disapears in the Router
DEBUG (0.000) None; args=()
Returning myDbCon: None
DEBUG (0.001) None; args=()
Returning myDbCon: None
DEBUG (0.001) None; args=()
Returning myDbCon: None
DEBUG (0.001) None; args=()
Returning myDbCon: None
DEBUG (0.001) None; args=()
Returning myDbCon: None
DEBUG (0.002) None; args=()
ERROR Internal Server Error: /app/env/list/    # It switches back to the default
Traceback (most recent call last):
  File "/.../lib64/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "/.../lib64/python3.6/site-packages/django/db/backends/mysql/base.py", line 71, in execute
    return self.cursor.execute(query, args)
  File "/.../lib64/python3.6/site-packages/MySQLdb/cursors.py", line 255, in execute
    self.errorhandler(self, exc, value)
  File "/.../lib64/python3.6/site-packages/MySQLdb/connections.py", line 50, in defaulterrorhandler
    raise errorvalue
  File "/.../lib64/python3.6/site-packages/MySQLdb/cursors.py", line 252, in execute
    res = self._query(query)
  File "/.../lib64/python3.6/site-packages/MySQLdb/cursors.py", line 378, in _query
    db.query(q)
  File "/.../lib64/python3.6/site-packages/MySQLdb/connections.py", line 280, in query
    _mysql.connection.query(self, query)
_mysql_exceptions.ProgrammingError: (1146, "Table 'app.myModel' doesn't exist")

The above exception was the direct cause of the following exception:

Update2： 这是使用会话的尝试。

我通过会话中的中间件存储数据库连接。在路由器中，我想访问请求的会话。我的期望是，Django 处理这个并且知道请求者。但我必须在 Session 键中给出

 s = SessionStore(session_key='???')

我没有到达路由器...

.middleware.py

from django.contrib.sessions.backends.file import SessionStore

class myMiddleware:

    def  process_view(self, request, view_func, view_args, view_kwargs):
        s = SessionStore()
        s['app.dbConnection'] = view_kwargs['MY_DATABASE']
        s.create()    

.myRouter.py

class myRouter:
    def db_for_read(self, model, **hints):
        from django.contrib.sessions.backends.file import SessionStore
        s = SessionStore(session_key='???')
        return s['app.dbConnection']

这与 threading.local 的结果相同......一个空值:-(

Answer 1

至少我有时间测试threadlocals包，它适用于 Django 2.1 和 Python 3.6.3。

.app/中间件.py

from threadlocals.threadlocals import set_request_variable

try:
    from django.utils.deprecation import MiddlewareMixin
except ImportError:
    MiddlewareMixin = object

class MyMiddleware(MiddlewareMixin):
    def  process_view(self, request, view_func, view_args, view_kwargs):
        set_request_variable('dbConnection', view_kwargs['environment'])

...

.app/路由器.py

from threadlocals.threadlocals import get_request_variable

class MyRouter:
    def db_for_read(self, model, **hints):
        if model._meta.app_label == 'app':
            return get_request_variable("dbConnection")
        return None
...