知识图谱使用Python驱动访问Neo4j
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前言
neo4j官方驱动支持Python语言,驱动程序主要包含Driver类型和Session类型。
Driver对象包含Neo4j数据库的详细信息,包括主机url、安全验证等配置,还管理着连接池(Connection Pool);
Session对象是执行事务单元的逻辑上下文,事务是在Session的上下文中执行的。由于Session不是线程安全的,并能够从Driver对象管理的连接池中回收利用(Recycle)连接,因此,Session对象是轻量级的(lightweight),用完之后应立即销毁(disposable)。
1. 安装Python版本的Neo4j驱动
如果不关注驱动的版本,可以安装最新版本的Python驱动。
pip install neo4j-driver
也可以在pip命令中指定python驱动的版本:
pip install neo4j-driver==$PYTHON_DRIVER_VERSION
pip install neo4j-driver==1.4.0
2. Driver对象
在安装neo4j驱动之后,在python代码中导入GraphDatabase模块,用于查询和更新图数据库:
from neo4j.v1 import GraphDatabase
1,创建Driver对象实例
输入neo4j数据库的uri,用户的安全验证,实例化Driver对象,并创建连接池:
from neo4j.v1 import GraphDatabase
uri = "bolt://localhost:7687"
_driver = GraphDatabase.driver(uri, auth=("neo4j", "password"))
使用close()函数关闭Driver对象分配的任何连接:
_driver.close()
2,使用Driver对象来创建Session对象
Driver对象从连接池中分配连接,创建Session对象:
_session = _driver.session()
3. Session对象
Session的创建是一个轻量级的操作,由于Session不是线程安全的,因此,Session通常应该在单个线程中短暂存续,用完之后立即销毁。
在Python中,推荐在with上下文中创建和销毁Session对象:
def add_person(name):
with _driver.session() as session:
session.run("CREATE (a:Person {name: $name})", name=name)
Session对象是执行事务的逻辑上下文,Cypher支持两种方式来提交事务。
1,以自动提交方式提交事务
以自动提交事务的方式执行Cypher查询,在Session对象执行Cypher语句之后,事务立即提交,因此,一次事务只能执行一个Cyper查询,返回的结果是StatementResult对象:
_session.run(statement, parameters=None)
2,以事务函数方式来提交事务
事务函数包含事务的工作单元,以事务函数方式提交事务是neo4j推荐的提交事务的方式,在事务函数方式中,一个事务可以执行多个Cypher查询。
首先,定义事务函数,传递相应的参数(Cypher语句和参数):
def create_person_node(tx, name):
tx.run("CREATE (a:Person {name: $name}) RETURN id(a)", name=name)
然后,在Session对象中启动写事务(write_transaction)来调用事务函数,返回的结果是StatementResult对象:
def add_person(driver, name):
with _driver.session() as session:
# Caller for transactional unit of work
return session.write_transaction(create_person_node, name)
4. StatementResult和Record
Session对象执行Cypher查询的结果是StatementResult类型,该类型实际上是由Record对象构成的集合,该类型的常用函数如下:
- keys():是由Record集合的Key构成的元组
- records():是由Record对象构成的集合
- single():从result变量中获取下一个记录,返回值是下一个Record或None
- peek():从结果中获取下一个Record对象,而该对象仍然保留在结果缓存中,以便后续进行处理。
Record类型是一个有序的Key/Value
对的序列,这意味着,Record对象类似于由Key:Value构成的列表,Key字段的值可以通过字段名称或索引来访问:
- items() :是由元组(key,value)构成的列表
- keys():是由一个Record对象的key构成的元组
- values():是由一个Record对象的value构成的元组
- index(key):返回指定Key在Record对象内的索引
5. 示例代码
class BookmarksExample(object):
def __init__(self, uri, user, password):
self._driver = GraphDatabase.driver(uri, auth=(user, password))
def close(self):
self._driver.close()
# Create a person node.
@classmethod
def create_person(cls, tx, name):
tx.run("CREATE (:Person {name: $name})", name=name)
# Create an employment relationship to a pre-existing company node.
# This relies on the person first having been created.
@classmethod
def employ(cls, tx, person_name, company_name):
tx.run("MATCH (person:Person {name: $person_name}) "
"MATCH (company:Company {name: $company_name}) "
"CREATE (person)-[:WORKS_FOR]->(company)",
person_name=person_name, company_name=company_name)
# Create a friendship between two people.
@classmethod
def create_friendship(cls, tx, name_a, name_b):
tx.run("MATCH (a:Person {name: $name_a}) "
"MATCH (b:Person {name: $name_b}) "
"MERGE (a)-[:KNOWS]->(b)",
name_a=name_a, name_b=name_b)
# Match and display all friendships.
@classmethod
def print_friendships(cls, tx):
result = tx.run("MATCH (a)-[:KNOWS]->(b) RETURN a.name, b.name")
for record in result:
print("{} knows {}".format(record["a.name"] ,record["b.name"]))
def main(self):
saved_bookmarks = [] # To collect the session bookmarks
# Create the first person and employment relationship.
with self._driver.session() as session_a:
session_a.write_transaction(self.create_person, "Alice")
session_a.write_transaction(self.employ, "Alice", "Wayne Enterprises")
saved_bookmarks.append(session_a.last_bookmark())
# Create the second person and employment relationship.
with self._driver.session() as session_b:
session_b.write_transaction(self.create_person, "Bob")
session_b.write_transaction(self.employ, "Bob", "LexCorp")
saved_bookmarks.append(session_b.last_bookmark())
# Create a friendship between the two people created above.
with self._driver.session(bookmarks=saved_bookmarks) as session_c:
session_c.write_transaction(self.create_friendship, "Alice", "Bob")
session_c.read_transaction(self.print_friendships)
class Neo4jProvider:
def __init__(self, uri, user, password):
self._driver = GraphDatabase.driver(uri, auth=(user, password))
def close(self):
self._driver.close()
def add_greeting_node(self, message):
with self._driver.session() as session:
session.write_transaction(self._create_greeting, message)
@staticmethod
def _create_greeting(tx, message):
tx.run("CREATE (a:Greeting) SET a.message = $message ", message=message)
参考:https://www.cnblogs.com/ljhdo/p/10907941.html
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