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I am trying to update the neo4j-flask application to Py2Neo V4 and i could not find how the "find_one" function has been replaced. (Nicole White used Py2Neo V2)

My setup:

  • Ubuntu 18.04
  • Python 3.6.5
  • Neo4j Server version: 3.4.6 (community)

Requirements.txt (the rest of the code is from github repository by Nicole White):

atomicwrites==1.2.0
attrs==18.1.0
backcall==0.1.0
bcrypt==3.1.4
certifi==2018.8.24
cffi==1.11.5
click==6.7
colorama==0.3.9
decorator==4.3.0
Flask==1.0.2
ipykernel==4.8.2
ipython==6.5.0
ipython-genutils==0.2.0
itsdangerous==0.24
jedi==0.12.1
Jinja2==2.10
jupyter-client==5.2.3
jupyter-console==5.2.0
jupyter-core==4.4.0
MarkupSafe==1.0
more-itertools==4.3.0
neo4j-driver==1.6.1
neotime==1.0.0
parso==0.3.1
passlib==1.7.1
pexpect==4.6.0
pickleshare==0.7.4
pkg-resources==0.0.0
pluggy==0.7.1
prompt-toolkit==1.0.15
ptyprocess==0.6.0
py==1.6.0
py2neo==4.1.0
pycparser==2.18
Pygments==2.2.0
pytest==3.7.3
python-dateutil==2.7.3
pytz==2018.5
pyzmq==17.1.2
simplegeneric==0.8.1
six==1.11.0
tornado==5.1
traitlets==4.3.2
urllib3==1.22
wcwidth==0.1.7
Werkzeug==0.14.1

Error i received when register user:

AttributeError: 'Graph' object has no attribute 'find_one'

"The User.find() method uses py2neo’s Graph.find_one() method to find a node in the database with label :User and the given username, returning a py2neo.Node object. "

In Py2Neo V3 the function find_one -> https://py2neo.org/v3/database.html?highlight=find#py2neo.database.Graph.find_one is available.

In Py2Neo V4 https://py2neo.org/v4/matching.html there is not find function anymore.

Someone got an idea on how to solve it in V4 or is downgrading here the way to go?

sentence
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otluk
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4 Answers4

2

py2neo v4 has a first function that can be used with a NodeMatcher. See: https://py2neo.org/v4/matching.html#py2neo.matching.NodeMatch.first

That said... v4 has introduced GraphObjects which (so far at least) I've found pretty neat.

In the linked github example Users are created with:

user = Node('User', username=self.username, password=bcrypt.encrypt(password))
graph.create(user)

and found with 

user = graph.find_one('User', 'username', self.username)

In py2neo v4 I would do this with

class User(GraphObject):
    __primarykey__ = "username"

    username = Property()
    password = Property()

 lukas = User()
 lukas.username = "lukasott"
 lukas.password = bcrypt.encrypt('somepassword')
 graph.push(lukas)

and

user = User.match(graph, "lukasott").first()

The first function, as I understand it, provides the same guarantees that find_one, as quoted from the v3 docs "and does not fail if more than one matching node is found."

Sean Peters
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  • My open point here is: class User(GraphObject): NameError: name 'GraphObject' is not defined -> Thought i could do from py2neo import GraphObject – otluk Aug 28 '18 at 13:57
  • Ok solved with: from py2neo.ogm import GraphObject, Property, Label – otluk Aug 28 '18 at 14:02
2

This worked for me instead. reference the link below

def find(self):
        user = graph.nodes.match("User", self.username).first()
        return user

https://py2neo.org/v5/_modules/py2neo/database.html

Tirth Patel
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Anthony Oluitan
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2

Another simpler way to solve this would be to replace find_one with the below:

from py2neo import Graph, NodeMatcher
matcher = NodeMatcher(graph)

user = matcher.match('user', name='name').first()
jyoti
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  • So this is a replacement for v3 syntax: user = graph.find_one("user", "name", "John") Thanks! works perfectly! – Tms91 Dec 10 '20 at 23:15
1

Building on the answer above, here is a minimal example showing the use of self.match().first() instead of find_one(). The attributes are set with Property() to provide an accessor to the property of the underlying node. (Documentation here: https://py2neo.org/v4/ogm.html#py2neo.ogm.Property)

from py2neo import Graph, Node
from passlib.hash import bcrypt

from py2neo.ogm import GraphObject, Property

graph = Graph()


class User(GraphObject):
    __primarykey__ = 'username'

    username = Property()
    password = Property()

    def __init__(self, username):
        self.username = username

    def find(self):
        user = self.match(graph, self.username).first()
        return user

    def register(self, password):
        if not self.find():
            user = Node('User', username=self.username, password=bcrypt.encrypt(password))
            graph.create(user)
            return True
        else:
            return False
BigRig
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