CODEWITHSUNDEEP
pythonflaskneo4j
phynfo
phynfo

Reputation: 4938

Minimal Flask-Example using Python Neo4j-Embedded

I was not able to implement a working minimal example with the Python Micro-Webframework Flask using a neo4j graphdatabase via the embedded python bindings (neo4j / python-embedded, version 1.6). What I have (on the basis of this Stack-Overflow-thread) is: 

import os
import jpype
from neo4j import GraphDatabase
from flask import Flask, g

# configuration
DATABASE = 'graphdatabase'
DEBUG = True
SECRET_KEY = 'blubber'
USERNAME = 'tobias'
PASSWORD = 'bla'
ADMIN = 'admin'

app = Flask(__name__)
app.config.from_object(__name__)

def connectDB(): 
    return GraphDatabase(app.config['DATABASE'])

def initDB():
    db = connectDB()
    with db.transaction:
        users = db.node()
        userIndex = db.node.indexes.create('users')
        user = db.node(name=app.config['ADMIN'])
        userIndex['name'][app.config['ADMIN']] = user
    db.shutdown()
    print "Database initialized."

@app.before_request
def before_request():
    jpype.attachThreadToJVM()
    g.db = connectDB()

@app.teardown_request
def teardown_request(exception):
    jpype.attachThreadToJVM()
    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']
    return render_template('index.html', name=username)

if os.path.exists(app.config['DATABASE']) == False:
    initDB()

if __name__ == '__main__':
  app.run()

Unfortunately, it throws: 

    File "/home/tobias/Esk/Dev/adhocracyLight/venv/lib/python2.7/site-packages/flask/app.py", line 1518, in __call__
return self.wsgi_app(environ, start_response)
File "/home/tobias/Esk/Dev/adhocracyLight/venv/lib/python2.7/site-packages/flask/app.py", line 1506, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/home/tobias/Esk/Dev/adhocracyLight/venv/lib/python2.7/site-packages/flask/app.py", line 1504, in wsgi_app
response = self.full_dispatch_request()
File "/home/tobias/Esk/Dev/adhocracyLight/venv/lib/python2.7/site-packages/flask/app.py", line 1264, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/tobias/Esk/Dev/adhocracyLight/venv/lib/python2.7/site-packages/flask/app.py", line 1262, in full_dispatch_request
rv = self.dispatch_request()
File "/home/tobias/Esk/Dev/adhocracyLight/venv/lib/python2.7/site-packages/flask/app.py", line 1248, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/tobias/Esk/Dev/adhocracyLight/adhocracyLight.py", line 73, in index
userIndex = g.db.node.indexes.get('users')
File "/home/tobias/Esk/Dev/adhocracyLight/venv/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.

I guess the problem is due to the threading (g is thread-local and contains a pointer to the neo4j-Database, maybe that's a bad idea?).

Upvotes: 3

Views: 3027

Answers (1)

espeed
espeed

Reputation: 4824

Neo4j Embedded is not intended to be used in a Web server environment -- you should use Neo4j Server and a Neo4j Server client.

Bulbs (http://bulbflow.com) is a Neo4j Server client that was designed with Flask in mind, in fact bulbflow.com is running on Flask on Heroku, using the Neo4j Heroku Add On (which is currently free).

You use Gremlin or Cypher for queries and transactional requests.

For an example of how to structure your app, see the Lightbulb (https://github.com/espeed/lightbulb) blog example, esp:

Notice this line in bulbsconf.py:

bulbs_config.set_neo4j_heroku()

Lightbulb is designed to run on Heroku with the Neo4j Heroku Add On -- leave that line out if you are not running on Heroku.

Then in your Flask views or your app.py, do:

from bulbsconf import graph

Upvotes: 3

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