python 操作 neo4j 的三步法

1. 定义单实例的driver对象，在python应用中利用此driver完成neo4j的操作

from neo4j import GraphDatabase
driver = GraphDatabase.driver(uri, auth=(username, password))
# 可以检查连接状态
driver.verify_connectivity()

2. 定义工作单元函数 Unit of Work

该函数接收的第一个参数是tx，代表driver对应的事务对象。内部一般是由三部分构成，分别是cypher字符串，tx.run()语句和返回值。cypher字符串的变量可以用 .format 带入，也可以用$占位，然后利用tx.run(cypher,params)的参数params完成字符变量替换。

# 读
def get_movies(tx, sort, order, limit, skip, user_id):  
    cypher = """  
        MATCH (m:Movie)        
        WHERE exists(m.`{0}`)        
        RETURN m {{ .* }} AS movie        
        ORDER BY m.`{0}` {1}        
        SKIP $skip        
        LIMIT $limit    
        """.format(sort, order)  
  
    result = tx.run(cypher, limit=limit, skip=skip, user_id=user_id)  
    return [row.value("movie") for row in result]

# 写
def create_user(tx, email, encrypted, name): 
    return tx.run("""
        CREATE (u:User { 
            userId: randomUuid(), 
            email: $email, 
            password: $encrypted, 
            name: $name 
        }) 
        RETURN u 
        """, 
        email=email, 
        encrypted=encrypted,
        name=name 
         ).single() 

3. 利用事务执行单元函数

# 读
with self.driver.session() as session:  
    return session.read_transaction(get_movies, sort, order, limit, skip, user_id)

# 写
with self.driver.session() as session:
    result = session.write_transaction(
        create_user, 
        email, 
        encrypted, 
        name
    )
    user = result['u']

当然，这里也可以自定义错误处理

# Import the Exception classes from neo4j.exceptions
from neo4j.exceptions import Neo4jError, ConstraintError

# Attempt a query
try:
    tx.run(cypher, params)
except ConstraintError as err:
    print("Handle constaint violation")
    print(err.code)  
    print(err.message) 
except Neo4jError as err:
    print("Handle generic Neo4j Error")
    print(err.code)  
    print(err.message)