python - 数据被插入到 MySQL 但不是永久的 - Python

Question

我正在使用 MySQLdb 来操作一个 MySQL 数据库，我有下面的例程，将一些数据注入(inject)到一个名为 urls 的表中>:

def insert_urls(dbconn, filenames):
    root = "<path>/"
    link = "http://<url>/"
    for f in filenames:
        filename = root + f + ".html"
        local_url = link + f + ".html"
        print(filename, local_url)
        sql = """
        INSERT INTO urls(url, filename) VALUES('%s', '%s');
        """ % (local_url, filename)
        print(sql)
        dbconn.execute_query(sql)

urls 表的声明位于此处:

def create_urls_table():

    sql = """
        CREATE TABLE IF NOT EXISTS urls (
            id INT NOT NULL AUTO_INCREMENT,
            url BLOB NOT NULL,
            filename BLOB NOT NULL,
            PRIMARY KEY(id)
        ) ENGINE=INNODB;
    """
    return sql

dbconn是Dbconn类的一个对象，定义为:

class Dbconn:
    def __init__(self,
                 host="",
                 user="",
                 pwd="",
                 database=""):

        self.host = host
        self.user = user
        self.pwd = pwd
        self.db = database
        self.cursor = None
        self.conn = None

        try:
            self.conn = MySQLdb.connect(host=self.host,
                                        user=self.user,
                                        passwd =self.pwd,
                                        db=self.db)
            self.cursor = self.conn.cursor()
            print "Connection established"
        except MySQLdb.Error, e:
            print "An error has occurred ", e

    def execute_query(self, sql=""):
        try:
            self.cursor.execute(sql)
        except MySQLdb.Error, e:
            print "An error has occurred ", e

运行过程 insert_urls 后，我得到以下输出:

  INSERT INTO urls(url, filename) VALUES ('http://<url>/amazon.html','<path>/amazon.html');
  INSERT INTO urls(url, filename) VALUES('http://<url>/linkedin.html', '<path>/linkedin.html');
  INSERT INTO urls(url, filename) VALUES('http://<url>/nytimes.html', '<path>/nytimes.html');

我可以通过命令行将其手动注入(inject) MySQL。但是，在执行 SELECT * FROM urls 查询时，我一无所获。手动插入两行后，我得到:

mysql> select * from urls;
+----+------------------------------------------------+------------------------+
| id | url                                            | filename               |
+----+------------------------------------------------+------------------------+
| 19 | http://<url>/yelp.html                         | <path>/yelp.html       |       
| 29 | http://<url>/amazon.html                       | <path>/amazon.html     |
+----+------------------------------------------------+------------------------+

请注意 id 值正在递增...这可能意味着数据正在插入，但没有持久化？有人可以帮我吗？

Answer 1

您可能正在使用事务数据库，在这种情况下您必须调用

self.conn.commit()

(的确，INNODB 是一个事务型数据库。)

---

您可以将 commit 合并到 execute_query 中:

def execute_query(self, sql=""):
    try:
        self.cursor.execute(sql)
    except MySQLdb.Error as e:
        print "An error has occurred ", e
        self.conn.rollback()
    else:
        self.conn.commit()

但是，在调用 commit 或 rollback 之前，您可能希望执行多个查询。在这种情况下，您可能希望从 execute_query 中删除 commit 并在需要时显式调用 commit，或者使用上下文管理器调用 当您退出 with 套件时提交。

---

请注意，MySQLdb 连接是上下文管理器。你可以写

connection = MySQLdb.connect(
    host=config.HOST, user=config.USER,
    passwd=config.PASS, db=config.MYDB, )

with connection as cursor:
    cursor.execute(...)

并且连接将在退出 with-suite 时调用 connection.commit()，或者 connection.rollback() 如果有一个异常(exception)。这是在 MySQLdb.connections.py 中控制它的代码:

def __enter__(self): return self.cursor()

def __exit__(self, exc, value, tb):
    if exc:
        self.rollback()
    else:
        self.commit()