如何检查 OpenSQLConnection 是否成功（在 Mathematica 中）？

发布于 2024-08-26 14:51:51 字数 183 浏览 2 评论 0原文

如何检查 DatabaseLink`OpenSQLConnection 是否成功？我的代码如下

conn = OpenSQLConnection[JDBC["hsqldb", "file"], "Name"-> "test"];

我可以使用类似 Head[conn] 的东西吗？

原文

How can I check if DatabaseLink`OpenSQLConnection was successful? My code is as follows

conn = OpenSQLConnection[JDBC["hsqldb", "file"], "Name"-> "test"];

Can I use something like Head[conn]?

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恬淡成诗 2024-09-02 14:51:51

成功连接的返回值将有头 SQLConnection （在 DatabaseLink 上下文中）

更一般地说：

OpenSQLConnection 返回 $Failed > 当连接由于任何原因失败时：

In[25]:= OpenSQLConnection[JDBC["mysql", "localhost:3306/foo"], 
   "Username" -> "foo", "Password" -> "bar"]

During evaluation of In[25]:= JDBC::error: Access denied for user 'foo'@'localhost' (using password: YES) >>

Out[25]= $Failed

...并且当其参数的形式不正确时未计算：

In[28]:= OpenSQLConnection[Sin[x]]

Out[28]= OpenSQLConnection[Sin[x]]

因此，您可以查找 $Failed 的返回值，也可以选择使用 检查[...]以捕获并处理生成的消息。正如您所猜测的，您可以使用 Head[returnvalue] 来确保返回值的头部不等于 OpenSQLConnection。

The return value for successful connection will have head SQLConnection (in the DatabaseLink context)

More generally:

OpenSQLConnection returns $Failed when the connection failed for whatever reason:

In[25]:= OpenSQLConnection[JDBC["mysql", "localhost:3306/foo"], 
   "Username" -> "foo", "Password" -> "bar"]

During evaluation of In[25]:= JDBC::error: Access denied for user 'foo'@'localhost' (using password: YES) >>

Out[25]= $Failed

... and unevaluated when its arguments were not of the proper form:

In[28]:= OpenSQLConnection[Sin[x]]

Out[28]= OpenSQLConnection[Sin[x]]

Therefore, you can look for a return value of $Failed and optionally also use Check[...] to trap and handle messages that were generated. As you guessed, you can use Head[returnvalue] to make sure the head of the return value does not equal OpenSQLConnection.

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酸甜透明夹心 2024-09-02 14:51:51

这并不完全是您问题的答案，但这是我为了可靠地连接到我的数据库所做的事情：

Needs["DatabaseLink`"];

CloseSQLConnection[conn];

TimeConstrained[
    conn=OpenSQLConnection[ JDBC["mysql","localhost:3306/mydb"],
                            "Username"->"myuser",
                            "Password"->"mypw"],
    5,
    CloseSQLConnection[conn];
    conn=OpenSQLConnection[ JDBC["mysql","localhost:3306/mydb"],
                            "Username"->"myuser",
                            "Password"->"mypw"]
];

This is not exactly an answer to your question, but this is what I do to connect reliably to my database:

Needs["DatabaseLink`"];

CloseSQLConnection[conn];

TimeConstrained[
    conn=OpenSQLConnection[ JDBC["mysql","localhost:3306/mydb"],
                            "Username"->"myuser",
                            "Password"->"mypw"],
    5,
    CloseSQLConnection[conn];
    conn=OpenSQLConnection[ JDBC["mysql","localhost:3306/mydb"],
                            "Username"->"myuser",
                            "Password"->"mypw"]
];

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