(Python，Neo4j-driver) -如何在检查节点不存在时返回none

Question

大家好，我对python中的neo4j( new 4j-driver)非常陌生。当检查节点是否不存在时，我遇到了一个问题，我通过这些代码发送了一些与db中的节点不匹配的名称。

from neo4j import GraphDatabase

driver = GraphDatabase.driver('bolt://localhost:7687', auth=(user, pass))
session = driver.session()


def matchNode(name):
   Label = 'SINGLE_NODE'
   return session.run("MATCH (a:"+Label+") WHERE a.name= $name " 
                      "RETURN id(a)", name=name).single().value()

name = 'test'
nodeID = matchNode(name)    
   if nodeID:
      print("Exist")
   else:
      print("Not Exist")

但它的错误如下所示，因为它在数据库中没有任何匹配的节点。

Traceback (most recent call last):
  File ".\neo4jdriver.py", line 44, in <module>
    props = matchNode(driver,'test')
  File ".\neo4jdriver.py", line 25, in matchNode
    "RETURN id(a)", name=name).single().value()
AttributeError: 'NoneType' object has no attribute 'value'
Failed to write data to connection Address(host='localhost', port=7687) (Address(host='127.0.0.1', port=7687)); ("0; 'Underlying socket connection gone (_ssl.c:2263)'")
Failed to write data to connection Address(host='localhost', port=7687) (Address(host='127.0.0.1', port=7687)); ("0; 'Underlying socket connection gone (_ssl.c:2263)'")
Failed to write data to connection Address(host='localhost', port=7687) (Address(host='127.0.0.1', port=7687)); ("0; 'Underlying socket connection gone (_ssl.c:2263)'")
Failed to write data to connection Address(host='localhost', port=7687) (Address(host='127.0.0.1', port=7687)); ("0; 'Underlying socket connection gone (_ssl.c:2263)'")
Failed to write data to connection Address(host='localhost', port=7687) (Address(host='127.0.0.1', port=7687)); ("0; 'Underlying socket connection gone (_ssl.c:2263)'")

那么，如果节点不存在，我该如何解决这个问题并返回none呢？谢谢

Answer 1

在matchNode函数中，执行一个try /except块，其中try返回session.run，except返回None