如何使用Python+SQLAlchemy远程连接MySQL数据库？

Question

我很难远程访问MySQL。我使用SSH隧道，希望使用Python+SQLALchemy连接数据库MySQL。

当我在控制台中使用MySQL客户端并指定“ptotocol=TCP”时，一切都很好！ 我使用命令：

mysql -h localhost —protocol=TCP -u USER -p

我可以通过SSH隧道访问远程数据库。

但是，当我想使用Python+SQLAchemy连接到数据库时，我找不到像—protocol=TCP这样的选项 否则，我只能连接到本地MySQL数据库。 请告诉我，有没有使用SQLAlchemy的方法。

Answer 1

这个问题的经典答案是使用主机的127.0.0.1或IP或主机名而不是“特殊名称”localhost。从documentation：

[...] connections on Unix to localhost are made using a Unix socket file by default

之后：

On Unix, MySQL programs treat the host name localhost specially, in a way that is likely different from what you expect compared to other network-based programs. For connections to localhost, MySQL programs attempt to connect to the local server by using a Unix socket file. This occurs even if a --port or -P option is given to specify a port number. To ensure that the client makes a TCP/IP connection to the local server, use --host or -h to specify a host name value of 127.0.0.1, or the IP address or name of the local server.

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然而，这个简单的技巧在您的情况下似乎不起作用，因此您必须以某种方式强制使用TCP套接字。正如您自己所解释的，在命令行上调用mysql时，使用--protocol tcp选项。

如here所述，从SQLAlchemy中，可以使用connect_args关键字参数将相关选项（如果有的话）作为URL选项或传递给驱动程序。

例如，使用PyMySQL，在为此目的而设置的测试系统（MariaDB 10.0.12、SQLAlchemy 0.9.8和PyMySQL 0.6.2）上，我得到了以下结果：

>>> engine = create_engine(
      "mysql+pymysql://sylvain:passwd@localhost/db?host=localhost?port=3306")
#                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
#                               Force TCP socket. Notice the two uses of `?`
#                               Normally URL options should use `?` and `&`  
#                               after that. But that doesn't work here (bug?)
>>> conn = engine.connect()
>>> conn.execute("SELECT host FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = CONNECTION_ID()").fetchall()
[('localhost:54164',)]

# Same result by using 127.0.0.1 instead of localhost: 
>>> engine = create_engine(
      "mysql+pymysql://sylvain:passwd@127.0.0.1/db?host=localhost?port=3306")
>>> conn = engine.connect()
>>> conn.execute("SELECT host FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = CONNECTION_ID()").fetchall()
[('localhost:54164',)]

# Alternatively, using connect_args:
>>> engine = create_engine("mysql+pymysql://sylvain:passwd@localhost/db",
                       connect_args= dict(host='localhost', port=3306))
>>> conn = engine.connect()
>>> conn.execute("SELECT host FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = CONNECTION_ID()").fetchall()
[('localhost:54353',)]

正如您所注意到的，两者都将使用TCP连接（我知道这是因为主机名后面的端口号）。另一方面：

>>> engine = create_engine(
      "mysql+pymysql://sylvain:passwd@localhost/db?unix_socket=/path/to/mysql.sock")
#                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
#                               Specify the path to mysql.sock in
#                               the `unix_socket` option will force
#                               usage of a UNIX socket

>>> conn = engine.connect()
>>> conn.execute("SELECT host FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = CONNECTION_ID()").fetchall()
[('localhost',)]

# Same result by using 127.0.0.1 instead of localhost: 
>>> engine = create_engine(
      "mysql+pymysql://sylvain:passwd@127.0.0.1/db?unix_socket=/path/to/mysql.sock")
>>> conn = engine.connect()
>>> conn.execute("SELECT host FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = CONNECTION_ID()").fetchall()
[('localhost',)]

# Alternatively, using connect_args:
>>> engine = create_engine("mysql+pymysql://sylvain:passwd@localhost/db",
                       connect_args= dict(unix_socket="/path/to/mysql.sock"))
>>> conn = engine.connect()
>>> conn.execute("SELECT host FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = CONNECTION_ID()").fetchall()
[('localhost',)]

主机名后没有端口：这是一个UNIX套接字。

Answer 2

在我的设置中（我使用mysql python），只使用127.0.0.1而不是mysql SQLAlchemy url中的localhost。我使用的完整url正是针对该场景（带有本地端口3307的隧道）的：

mysql:/user:passwd@127.0.0.1:3307/

我使用的是SQLAlchemy 1.0.5，但我想这并不重要。。。