Node.js 和 node-mysql DB 查询 - 需要同步代码帮助

发布于 2024-11-09 02:23:59 字数 636 浏览 0 评论 0原文

我正在编写一些非 Web 应用程序帮助程序，并且遇到了同步查询调用的需要。

基本上，在一个循环中，我需要检查数据库以查看该值是否存在。如果没有，则插入该值。目前，对于node-mysql，我只能让它与回调一起工作。因此，node.js 将调用视为异步，并在查询完成之前继续处理我的请求。这是一个大问题，因为最终可能会插入重复项，因为它们在队列中。

理想的解决方案 - 不起作用。结果实际上是客户端的对象，我在里面找不到实际的结果。然而，这确实使其同步。

results = client.query('SELECT COUNT(md5) as md5Count FROM table WHERE md5 = "' + md5 + '"')

以下不起作用。 Node.js 将其视为异步，outerResult 仍然是 client 的对象。

outerResult = client.query('SELECT COUNT(md5) as md5Count FROM board WHERE md5 = "' + md5 + '"',  function  selectCb(err, results, fields) {console.log(results);});

任何帮助表示赞赏。

原文

I am writing some non-web app helper, and came across a need for a synchronous query call.

Basically, within a loop I need to check the database to see if the value exists. If it doesn't then insert the value. Currently, with node-mysql I can only get it to work with a callback. Because of that, node.js treats the call as asynchronous and keeps processing my request before the query is finished. This is a big issue because in the end it could be inserting duplicates because they were in the queue.

Ideal Solution - doesn't work. Results is actually the object of client, and I can't find the actual results within. However this does make it synchronous.

results = client.query('SELECT COUNT(md5) as md5Count FROM table WHERE md5 = "' + md5 + '"')

The following does not work. Node.js treats it as asynchronous, and outerResult is still the object of client.

outerResult = client.query('SELECT COUNT(md5) as md5Count FROM board WHERE md5 = "' + md5 + '"',  function  selectCb(err, results, fields) {console.log(results);});

Any help is appreciated.

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深海不蓝 2024-11-16 02:23:59

基本上，在循环内我需要检查数据库以查看该值是否存在。如果没有，则插入该值。

这个问题最好用 SQL 来解决。您不能通过重复与数据库对话来解决此问题，而是通过让 SQL 仅在索引值尚不存在的位置插入来解决此问题。

INSERT INTO mytable ( name, address ) 
SELECT @name, @address FROM DUAL 
WHERE NOT EXISTS (SELECT * FROM mytable WHERE name = @name, address = @address)

这是一个超级简化的示例，并不是最优化的。如果您愿意，您可以在这里对数据集执行相同的操作，而不是逐条记录。

Basically, within a loop I need to check the database to see if the value exists. If it doesn't then insert the value.

This is a problem best served with SQL. You don't solve this problem by talking to the database repeatedly, you solve this problem by having SQL only insert where the index value doesn't already exist.

INSERT INTO mytable ( name, address ) 
SELECT @name, @address FROM DUAL 
WHERE NOT EXISTS (SELECT * FROM mytable WHERE name = @name, address = @address)

This is a super simplified example, and not the most optimized. You can do the same thing here with sets of data, instead of record by record, if you like.

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