使用Flask的SQLAlchemy会话引发了“线程中创建的SQLite对象只能在同一个线程中使用” [英] Using SQLAlchemy session from Flask raises "SQLite objects created in a thread can only be used in that same thread"
问题描述
我有一个Flask视图,它使用SQLAlchemy来查询和显示一些博客文章。我使用mod_wsgi运行我的应用程序。这个视图是我第一次进入页面,但下一次返回500错误。回溯显示错误 ProgrammingError:在线程中创建的SQLite对象只能在同一个线程中使用。
为什么我得到这个错误,我该如何解决? p>
views.py
engine = create_engine('sqlite:////var/www/homepage/blog.db')
Base.metadata.bind = engine
DBSession = sessionmaker(bind = engine)
session = DBSession()
@ app.route('/ blog')
@ app.route('/ blog.html')
def blog()
entrys = session.query(Entry).order_by(desc(Entry.timestamp))。all()
return render_template('blog.html',blog_entrys = entrys)
models.py
:
类Entry(Base):
__tablename__ ='entry'
$ b id = Column(Integer,primary_key = True)
title = Column(String(100),nullable = False)
body = Column(String,nullable = False)
timestamp = Column(DateTime, nullable = False)
featured = Column(Boolean,nullable = False)
comments = relationship('Comment')
$ b $ def is_featured(self):
return self.featured
class Comment(Base):
__tablename__ ='comment'
$ b $ id = Column(Integer,primary_key = True )
entry_id = Column(Integer,ForeignKey('entry.id'))
$ b $ text = Column(String(500),nullable = False)
name = Column (80))
engine = create_engine('sqlite:////var/www/homepage/blog.db')
Base.metadata.create_all(引擎)
.html [GET]
Traceback(最近一次调用的最后一个):
在wsgi_app $ b中的文件/usr/lib/python2.6/dist-packages/flask/app.py,第861行$ b rv = self.dispatch_request()
文件/usr/lib/python2.6/dist-packages/flask/app.py,第696行,在dispatch_request
返回self.view_functions [rule .endpoint]( ** req.view_args)
文件/var/www/homepage/webserver.py,第38行,在博客
entrys = session.query(Entry).order_by(desc(Entry.timestamp) ).all()
文件/usr/lib/python2.6/dist-packages/sqlalchemy/orm/query.py,行1453,在所有
返回列表(self)
文件/usr/lib/python2.6/dist-packages/sqlalchemy/orm/query.py,第1565行,在__iter__
中返回self._execute_and_instances(context)
文件/ usr / lib / python2.6 / dist-packages / sqlalchemy / orm / query.py,第1570行,在_execute_and_instances
mapper = self._mapper_zero_or_none())
文件/usr/lib/python2.6 /dist-packages/sqlalchemy/orm/session.py,第735行,执行
子句,params或{})
文件/usr/lib/python2.6/dist-packages/sqlalchemy /engine/base.py,第1157行,执行
params)
文件/usr/lib/python2.6/dist-packages/sqlalchemy/engine/base.py,第1235行,在_execute_clauseelement中
parameters = params
文件/usr/lib/python2.6/dist-packages/s qlalchemy / engine / base.py,第1348行,在__create_execution_context
无,无)
文件/usr/lib/python2.6/dist-packages/sqlalchemy/engine/base.py,第1343行,在__create_execution_context
connection = self,** kwargs)
文件/usr/lib/python2.6/dist-packages/sqlalchemy/engine/default.py,第381行,在__init__
self.cursor = self.create_cursor()
文件/usr/lib/python2.6/dist-packages/sqlalchemy/engine/default.py,第523行,在create_cursor
返回self._connection.connection.cursor()
在游标
c = self.connection中的文件/usr/lib/python2.6/dist-packages/sqlalchemy/pool.py,行383。游标(* args,** kwargs)
ProgrammingError:(ProgrammingError)在一个线程中创建的SQLite对象只能在同一个线程中使用。该对象是在线程ID 140244498364160中创建的,这是线程ID 140244523542272 None [ }]
SQLAlchemy所以)如果您跨线程共享会话不起作用。您可能不会显式地使用线程,但是 mod_wsgi
是,并且已经定义了一个全局会话
对象。请使用 scoped_session
为每个线程处理创建一个独特的会话。
$ p $ session $ scoped_session(sessionmaker(bind = engine))
@ app.teardown_request
def remove_session(ex = None):
session.remove()
@ app.route('/')
def example():
item = session.query(MyModel).filter(...)。all()
...
最好使用 Flask-SQLAlchemy 来处理这个和其他的东西给你。 SQLAlchemy文档建议您使用集成库,而不是自己做。
db = SQLAlchemy(app)
@ app.route('/')
def example():
item = db.session.query(MyModel).filter(...)。all()
...
另外请注意,您应该只定义一次引擎,会话等并导入它在其他地方,而不是像你现有的代码重新定义在每个文件中。
I have a Flask view which uses SQLAlchemy to query and display some blog posts. I am running my app using mod_wsgi. This view works the first time I go to the page, but returns a 500 error next time. The traceback shows the error ProgrammingError: SQLite objects created in a thread can only be used in that same thread.
Why am I getting this error and how do I fix it?
views.py
engine = create_engine('sqlite:////var/www/homepage/blog.db')
Base.metadata.bind = engine
DBSession = sessionmaker(bind = engine)
session = DBSession()
@app.route('/blog')
@app.route('/blog.html')
def blog():
entrys = session.query(Entry).order_by(desc(Entry.timestamp)).all()
return render_template('blog.html', blog_entrys = entrys)
models.py
:
class Entry(Base):
__tablename__ = 'entry'
id = Column(Integer, primary_key = True)
title = Column(String(100), nullable = False)
body = Column(String, nullable = False)
timestamp = Column(DateTime, nullable = False)
featured = Column(Boolean, nullable = False)
comments = relationship('Comment')
def is_featured(self):
return self.featured
class Comment(Base):
__tablename__ = 'comment'
id = Column(Integer, primary_key = True)
entry_id = Column(Integer, ForeignKey('entry.id'))
text = Column(String(500), nullable = False)
name = Column(String(80))
engine = create_engine('sqlite:////var/www/homepage/blog.db')
Base.metadata.create_all(engine)
Exception on /blog.html [GET]
Traceback (most recent call last):
File "/usr/lib/python2.6/dist-packages/flask/app.py", line 861, in wsgi_app
rv = self.dispatch_request()
File "/usr/lib/python2.6/dist-packages/flask/app.py", line 696, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/var/www/homepage/webserver.py", line 38, in blog
entrys = session.query(Entry).order_by(desc(Entry.timestamp)).all()
File "/usr/lib/python2.6/dist-packages/sqlalchemy/orm/query.py", line 1453, in all
return list(self)
File "/usr/lib/python2.6/dist-packages/sqlalchemy/orm/query.py", line 1565, in __iter__
return self._execute_and_instances(context)
File "/usr/lib/python2.6/dist-packages/sqlalchemy/orm/query.py", line 1570, in _execute_and_instances
mapper=self._mapper_zero_or_none())
File "/usr/lib/python2.6/dist-packages/sqlalchemy/orm/session.py", line 735, in execute
clause, params or {})
File "/usr/lib/python2.6/dist-packages/sqlalchemy/engine/base.py", line 1157, in execute
params)
File "/usr/lib/python2.6/dist-packages/sqlalchemy/engine/base.py", line 1235, in _execute_clauseelement
parameters=params
File "/usr/lib/python2.6/dist-packages/sqlalchemy/engine/base.py", line 1348, in __create_execution_context
None, None)
File "/usr/lib/python2.6/dist-packages/sqlalchemy/engine/base.py", line 1343, in __create_execution_context
connection=self, **kwargs)
File "/usr/lib/python2.6/dist-packages/sqlalchemy/engine/default.py", line 381, in __init__
self.cursor = self.create_cursor()
File "/usr/lib/python2.6/dist-packages/sqlalchemy/engine/default.py", line 523, in create_cursor
return self._connection.connection.cursor()
File "/usr/lib/python2.6/dist-packages/sqlalchemy/pool.py", line 383, in cursor
c = self.connection.cursor(*args, **kwargs)
ProgrammingError: (ProgrammingError) SQLite objects created in a thread can only be used in that same thread.The object was created in thread id 140244498364160 and this is thread id 140244523542272 None [{}]
SQLAlchemy (and in this case SQLite also) doesn't work if you share a session across threads. You may not be using threads explicitly, but mod_wsgi
is, and you've defined a global session
object. Either use scoped_session
to handle creating a unique session for each thread.
session = scoped_session(sessionmaker(bind=engine))
@app.teardown_request
def remove_session(ex=None):
session.remove()
@app.route('/')
def example():
item = session.query(MyModel).filter(...).all()
...
Preferably, use Flask-SQLAlchemy which handles this and other things for you. The SQLAlchemy docs recommend you use the integration library rather than doing this yourself.
db = SQLAlchemy(app)
@app.route('/')
def example():
item = db.session.query(MyModel).filter(...).all()
...
Also note that you should only be defining the engine, session, etc. once and importing it elsewhere, rather than redefining it in each file like your current code does.
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