如何在Flask微框架中使用Neo4j-embedded for Python (线程)？
我正在学习Flask教程(Flaskr)，以便尝试使用Neo4j-embedded for Python。这是在一个虚拟环境中。下面是我的“主”应用程序代码：
import os
import jpype
from neo4j import GraphDatabase
from flask import Flask, request, session, g, redirect, url_for, abort, render_template, flash
app = Flask(__name__)
app.config.from_pyfile(os.environ['APP_SETTINGS'])
def connectDB():
return GraphDatabase(app.config['DATABASE'])
def initDB():
db = connectDB()
with db.transaction:
users = db.node()
roles = db.node()
db.reference_node.USERS(users)
db.reference_node.ROLES(roles)
userIndex = db.node.indexes.create('users')
user = db.node(name=app.config['ADMIN'])
user.INSTANCE_OF(users)
userIndex['name'][app.config['ADMIN']] = user
role = db.node(type='superadmin')
role.INSTANCE_OF(roles)
role.ASSIGN_TO(user)
db.shutdown()
print "Database initialized."
def testDB():
db = connectDB()
with db.transaction:
userIndex = db.node.indexes.get('users')
user = userIndex['name'][app.config['ADMIN']].single
username = user['name']
db.shutdown()
print "Admin username is '%s'. Database exists." % username
@app.before_request
def before_request():
jpype.attachThreadToJVM()
g.db = connectDB()
@app.teardown_request
def teardown_request(exception):
g.db.shutdown()
@app.route('/')
def index():
with g.db.transaction:
userIndex = g.db.node.indexes.get('users')
user = userIndex['name'][app.config['ADMIN']].single
username = user['name']
fields = dict(username=username)
return render_template('index.html', fields=fields)
if os.path.exists(app.config['DATABASE']) == False:
initDB()
else:
testDB()initDB()和testDB()可以很好地工作--没有Gremlin、PyLucene等--只需要jpype和ne4j-embedded。最初，当我请求index()时，JVM会失败，应用程序会终止。我在网上搜索，了解到我需要在before_request()中添加"jpype.attachThreadToJVM()“行来解决Python线程化JVM的问题，并且应用程序不会终止。然而，这直接导致了另一个问题：
Traceback (most recent call last):
File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1518, in __call__
return self.wsgi_app(environ, start_response)
File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1506, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1504, in wsgi_app
response = self.full_dispatch_request()
File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1264, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1262, in full_dispatch_request
rv = self.dispatch_request()
File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1248, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/ht/dev/apps/evobox/evobox/__init__.py", line 68, in index
userIndex = g.db.node.indexes.get('users')
File "/ht/dev/envFlask/lib/python2.7/site-packages/neo4j/index.py", line 36, in get
return self._index.forNodes(name)
java.lang.RuntimeExceptionPyRaisable: java.lang.IllegalArgumentException: No index provider 'lucene' found. Maybe the intended provider (or one more of its dependencies) aren't on the classpath or it failed to load.谷歌搜索整个最后一行都没有结果。只需搜索"java.lang.IllegalArgumentException:找不到索引提供程序'lucene‘。“在python的上下文中没有任何结果。
索引索引似乎显示数据库打开了3次(initDB()、testDB()和neo4j ())。每个实例的类路径都是相同的：
Class Path: /ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-jmx-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-lucene-index-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-graph-matching-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-kernel-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/geronimo-jta_1.1_spec-1.1.1.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/lucene-core-3.1.0.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-graph-algo-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-udc-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-cypher-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/scala-library-2.9.0-1.jar我还将index()直接修改为connectDB和attachThreadToJVM，就像initDB()和testDB()一样，没有使用'g‘全局变量-这导致了完全相同的错误。
在一个线程请求上，而不是在'main‘应用程序中，我可能遗漏/忽略了什么？
注意:我知道使用py2neo或Rexster/Bulbs的RESTful Web Service解决方案，但我想暂时避免使用它。
编辑:使用JPype-0.5.4.2，Neo4j-embedded-1.5.b2，Java-6-openjdk
回答 2
Stack Overflow用户
发布于 2011-11-04 18:17:42
这种模式的一个问题是，启动指向同一位置的多个数据库有风险，这将导致问题。您需要的是遵循应用程序的整个生命周期的数据库的单个实例。
为什么它没有找到lucene提供商是一个很难回答的问题。索引提供程序是使用java服务加载器加载的，这意味着JPype不应该影响它。只要JVM启动正常，并且lucene-index实现jar在类路径上，它就应该可以工作。
这可能与线程有关，我目前正在编写一个修复程序来自动处理"attachThreadToJVM()“调用。我将添加一个测试用例，以确保从单独的线程读取索引也能像预期的那样工作。
线程工作当前在此邮件列表线程中保持更新：
http://neo4j-community-discussions.438527.n3.nabble.com/Neo4j-Python-embedding-problems-with-shutdown-and-threads-td3476163.html
Stack Overflow用户
发布于 2011-11-04 06:14:59
使用标准的java默认路径，使用干净的neo4j、flask和jpipe安装，尝试复制该错误。无法生成该日志。但是我得到了一个错误：
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "teststack.py", line 27, in initDB
userIndex = db.node.indexes.create('users')
File "/usr/local/lib/python2.7/dist-packages/neo4j/index.py", line 32, in create
return self._index.forNodes(name, to_java(config))
jpype._jexception.RuntimeExceptionPyRaisable: java.lang.IllegalArgumentException: Supplied index configuration:
{}
doesn't match stored config in a valid way:
{provider=lucene, type=exact}
for 'users'使用initDB时
修复为
userIndex = db.node.indexes.create(users)https://stackoverflow.com/questions/7999532
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