Flask-SQLAlchemy-快速连接到多个数据库 [英] Flask-SQLAlchemy - on the fly connections to multiple databases
问题描述
我有一个flask webapp
,用户可以在其中连接到自己的mysql数据库并查询自己的表
I have a flask webapp
where users will be able to connect to their own mysql databases and query their own tables
使用flask-sqlalchemy创建(到不同数据库的)多个连接的最佳方法是什么.似乎需要使用scoped_session
和sessionmaker
完成操作,但似乎无法将其包裹住.
What's the best way to create multiple connections (to different databases) using flask-sqlalchemy. It seems like it needs to be done with scoped_session
and sessionmaker
but cant seem to wrap my head around it.
问题的第二部分,一旦我为其中一个用户创建了与mysql db的连接,我如何在请求之间保持连接?
Also the second part of the question, once I create a connection to a mysql db for one of the users, how do i persist the connection across requests ?
当前,我将每个用户的连接字符串放在flask会话变量上,并在每个新请求下,依次创建引擎和连接
Currently, i put the connection string for each user on the flask session variable and at each new request, i create the engine and connection as such
engine = create_engine(connection_string, convert_unicode=True)
conn = engine.connect()
db_session = Session(bind=conn) # Session - i create it globally on the __init__ like this Session = scoped_session(sessionmaker()) and import it in the view
## Query using the db_session
这似乎对于创建引擎和与每个请求的连接都是非常浪费的-能否在请求之间保留该连接?
This seems super wasteful to create the engine and the connection with every request - cant the connection be persisted across requests ?
推荐答案
一个数据库
引擎是允许您使用连接池的引擎.默认情况下,它将在请求之间保持连接.基本用法(没有像scoped_session
或sessionmaker
这样的花哨的东西)是这样的:
One Database
The engine is what allows you to use connection pooling. By default, it will persist connections across requests. The basic usage (without fancy things like scoped_session
or sessionmaker
) is like this:
engine = create_engine(...)
@app.route(...)
def foo():
session = Session(bind=engine)
try:
session.query(...)
session.commit()
finally:
session.close()
return ""
在此之上,您可以添加scoped_session
和sessionmaker
:
On top of this, you can add scoped_session
and sessionmaker
:
engine = create_engine(...)
Session = sessionmaker(bind=engine)
session = scoped_session(Session, scopefunc=...)
@app.route(...)
def foo():
try:
session.query(...)
session.commit()
finally:
session.close()
return ""
flask-sqlalchemy
通过提供所有这些功能使您的生活更轻松:
flask-sqlalchemy
makes your life easier by providing all of this:
db = SQLAlchemy(app)
@app.route(...)
def foo():
db.session.query(...)
db.session.commit()
return ""
多个数据库
您可以轻松地将此概念扩展到多个数据库:
Multiple Databases
You can easily extend this concept to multiple databases:
engine1 = create_engine(...)
engine2 = create_engine(...)
@app.route(...)
def foo():
session = Session(bind=choose_engine_for_user())
try:
session.query(...)
session.commit()
finally:
session.close()
return ""
添加scoped_session
和sessionmaker
时:
engine1 = create_engine(...)
engine2 = create_engine(...)
Session1 = sessionmaker(bind=engine1)
Session2 = sessionmaker(bind=engine2)
session1 = scoped_session(Session1, scopefunc=...)
session2 = scoped_session(Session2, scopefunc=...)
@app.route(...)
def foo():
session = choose_session_for_user()
try:
session.query(...)
session.commit()
finally:
session.close()
return ""
当您有许多数据库时,这会有点烦人,在这种情况下,您可能应该编写一个注册表类来跟踪所有引擎和会话:
This gets a little annoying when you have many databases, in which case you should probably write a registry class to keep track of all the engines and sessions:
class SessionRegistry(object):
_registry = {}
def get(self, url, **kwargs):
if url not in self._registry:
engine = create_engine(url, **kwargs)
Session = session_maker(bind=engine)
session = scoped_session(Session, scopefunc=...)
self._registry[url] = session
return self._registry[url]
registry = SessionRegistry()
@app.route(...)
def foo():
session = registry.get(...)
try:
session.query(...)
session.commit()
finally:
session.close()
return ""
您需要在其之上添加某种LRU,以便不会无限创建引擎.
You'll need to add some kind of LRU on top of it so that there's no unbounded creation of engines.
flask-sqlalchemy
支持有限形式的多个数据库,其中每个模型都连接到不同的数据库.如果您愿意,请访问文档此处.
flask-sqlalchemy
has support for a limited form of multiple databases where each of your model connects to a different database. If this applies to you, the documentation is here.
这篇关于Flask-SQLAlchemy-快速连接到多个数据库的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!