Python MySQL ReferenceError：弱引用对象不再存在

Question

我想连接到 mySQL Server 并从 users 表中获取所有用户。但是如果我尝试执行我的代码，它会说：

/bin/python /home/luca/PycharmProjects/Test/sql.py
Traceback (most recent call last):
  File "/home/luca/PycharmProjects/Test/sql.py", line 18, in <module>
    for x in get_user_by_username("testuser"):
  File "/usr/lib/python3.8/site-packages/mysql/connector/cursor.py", line 861, in fetchone
    row = self._fetch_row()
  File "/usr/lib/python3.8/site-packages/mysql/connector/cursor.py", line 831, in _fetch_row
    if not self._have_unread_result():
  File "/usr/lib/python3.8/site-packages/mysql/connector/cursor.py", line 351, in _have_unread_result
    return self._connection.unread_result
ReferenceError: weakly-referenced object no longer exists

Process finished with exit code 1

这是我的代码

import mysql.connector


def get_user_by_username(username):
 mydb = mysql.connector.connect(
     host="localhost",
     user="testuser",
     passwd="k3gc8pHPvEtGqND",
     database="test"
 )

 mycursor = mydb.cursor()

 mycursor.execute("SELECT * FROM users")
 return mycursor


for x in get_user_by_username("testuser"):
    print(x)

为什么会发生这种情况，我该如何解决？

Answer 1

cursor 对象使用connection 对象。
当您的 get_user_by_username 函数完成执行时，
与 mysql 的连接已关闭，因此 cursor 也不存在。
让函数返回连接和光标都可以工作。

import mysql.connector

def get_user_by_username(username):
    mydb = mysql.connector.connect(
        host="localhost",
        user=username,
        passwd="k3gc8pHPvEtGqND",
        database="test"
        )

    mycursor = mydb.cursor()

    mycursor.execute("SELECT * FROM users")
    return mydb, mycursor

mydb, mycursor = get_user_by_username("testuser")
for x in mycursor:
    print(x)

Answer 2

你可以使用一个包含所有行的变量，并且在它上面有循环

import mysql.connector


def get_user_by_username(username):
 mydb = mysql.connector.connect(
     host="localhost",
     user="testuser",
     passwd="k3gc8pHPvEtGqND",
     database="test"
 )

 mycursor = mydb.cursor()

 mycursor.execute("SELECT * FROM users") 
 records = mycursor.fetchall()
 return records

for x in get_user_by_username("testuser"):
    print(x)

Answer 3

这基本上是因为“弱参考”而发生的，请在this DOC阅读更多相关信息

参考这段代码，它会像魅力一样工作：

import mysql.connector as connector

def connection():

    config = {
        "user": "dev_staq",
        "password": "dev_staq",
        "host": "localhost",
        "port": 3306,
        "database": "dev_staq"
    }
    try:
        c = connector.connect(**config)
        return c
    except:
        print "connection error"
        exit(1)


def test1(): #no error method
    cn = connection()
    cur = cn.cursor()
    cur.execute("select * from ulogin")
    print cur.fetchone()
test1()

如有任何疑问，请告诉我。谢谢。

Answer 4

我猜你可以像这样使用自己的连接器类

# do some imports
from mysql import connector

# Add connection and cursor wrapper
class MySQLConnector:
    conn=None
    cursor=None
        
    def __init__(self):
        self.conn=connector.connect(
            host="host",
            port="port",
            user="user",
            password="pass",
            database="database"
        )
        self.cursor=self.conn.cursor()

# Connect
myconn=MySQLConnector()

# Select from database
def getMyRows():
    myconn.cursor.execute("SELECT * FROM your_table WHERE something")
    row = myconn.cursor.fetchone()
    print(row)