NodeJS MySQL转储

我试图写一个基本的cron脚本来运行和“转储”一个mysql数据库。 出于某种原因，当“成功保存文件”时，它确实创build了文件，但是它是空的。 如果不是保存文件，我执行一个console.log，它打印一个空string。 任何想法，我可能做错了什么？

提前致谢。

var mysql_backup = function(){ this.backup = ''; this.mysql = require('mysql'), this.init = function(){ this.connection = this.mysql.createConnection({ user: 'root', password: 'root', database: 'test' }); } this.query = function(sql, callback) { this.connection.query(sql, function (error, results, fields) { if (error) { throw error; } if (results.length > 0) { callback(results); } }); } this.get_tables = function(callback){ var me = this; me.query('SHOW TABLES', function(tables) { for (var table in tables){ me.query( 'SHOW CREATE TABLE ' + tables[table].Tables_in_test, function(r){ for (var t in r) { me.backup += "DROP TABLE " + r[t].Table + "\n\n"; me.backup += r[t]["Create Table"] + "\n\n"; } } ) } me.save_backup(); }); } this.save_backup = function(){ var fs = require('fs'); fs.writeFile("./backup_test.txt", this.backup, function(err) { if(err) { console.log(err); } else { console.log("The file was saved!"); } }); } }; var db = new mysql_backup; db.init(); db.get_tables(); db.connection.destroy(); 

Answer 1

写的代码甚至没有为我保存文件。 似乎有几个问题。 不知道这是实际的代码还是在复制粘贴中丢失了一些东西。 不过，根据你所得到的：

一个重要的问题是，你永远不会用connection.connect（）连接到代码中的数据库。

你想连接运行的代码应该在connection.connect（）callback中。 例如

 connection.connect(function (err, empty) { if (err) throw new Error ('Panic'); // if no error, we are off to the races... } 

然而，即使你很快重构你的代码来包装你的最后一行代码，但是你仍然会遇到问题，因为你在各种SQL调用之前破坏了连接，所以你需要移动代码进入某种最后的callback。

即使这样做之后，仍然会有一个空文件，因为您从“SHOW TABLES”callback中调用了save_backup，而不是在您通过内部callback填充了CREATE TABLE语句并填充了备份属性。

这是你的代码的最小重写，这将做你想要的。 重要的是要注意的是pipe理何时写文件和closures连接的“计数器”。 如果是我的，我会做出其他更改，包括：

• 用“自我”而不是“我”
• 使用数字for循环而不是for（… in …）语法
• 有我自己的callback的节点惯例（错误，东西）
• 一个更实质性的变化是我会重写这个使用承诺，因为这样做可以免除你与深嵌套callback固有的困惑的一些悲伤。 我个人喜欢Q库，但是这里有几个选项。

希望这有助于。

 var mysql_backup = function(){ this.backup = ''; this.mysql = require('mysql'); this.init = function(){ this.connection = this.mysql.createConnection({ user : 'root', password : 'root', database : 'test' }); }; this.query = function(sql, callback) { this.connection.query(sql, function (error, results, fields) { if (error) { throw error; } if (results.length > 0) { callback(results); } }); }; this.get_tables = function(callback){ var counter = 0; var me = this; this.query('SHOW TABLES', function(tables) { for (table in tables){ counter++; me.query( 'SHOW CREATE TABLE ' + tables[table].Tables_in_mvc, function(r){ for (t in r) { me.backup += "DROP TABLE " + r[t].Table + "\n\n"; me.backup += r[t]["Create Table"] + "\n\n"; } counter--; if (counter === 0){ me.save_backup(); me.connection.destroy(); } } ) } }); }; this.save_backup = function(){ var fs = require('fs'); fs.writeFile("./backup_test.txt", this.backup, function(err) { if(err) { console.log(err); } else { console.log("The file was saved!"); } }); } }; var db = new mysql_backup; db.init(); db.connection.connect(function (err){ if (err) console.log(err); db.get_tables(function(x){;}); }); 

更新：如果您好奇，这是一个使用承诺严重评论的实现。 请注意，如果没有解释Q promise库函数的注释，它会比原始版本稍短，并且还提供更全面的error handling。

 var MysqlBackup = function(connectionInfo, filename){ var Q = require('q'); var self = this; this.backup = ''; // my personal preference is to simply require() inline if I am only // going to use something a single time. I am certain some will find // this a terrible practice this.connection = require('mysql').createConnection(connectionInfo); function getTables(){ // return a promise from invoking the node-style 'query' method // of self.connection with parameter 'SHOW TABLES'. return Q.ninvoke(self.connection,'query', 'SHOW TABLES'); }; function doTableEntries(theResults){ // note that because promises only pass a single parameter around, // if the 'denodeify-ed' callback has more than two parameters (the // first being the err param), the parameters will be stuffed into // an array. In this case, the content of the 'fields' param of the // mysql callback is in theResults[1] var tables = theResults[0]; // create an array of promises resulting from another Q.ninvoke() // query call, chained to .then(). Note that then() expects a function, // so recordEntry() in fact builds and returns a new one-off function // for actually recording the entry (see recordEntry() impl. below) var tableDefinitionGetters = []; for (var i = 0; i < tables.length ; i++){ // I noticed in your original code that your Tables_in_[] did not // match your connection details ('mvc' vs 'test'), but the below // should work and is a more generalized solution var tableName = tables[i]['Tables_in_'+connectionInfo.database]; tableDefinitionGetters.push(Q.ninvoke(self.connection, 'query', 'SHOW CREATE TABLE ' + tableName) .then(recordEntry(tableName)) ); } // now that you have an array of promises, you can use Q.allSettled // to return a promise which will be settled (resolved or rejected) // when all of the promises in the array are settled. Q.all is similar, // but its promise will be rejected (immediately) if any promise in the // array is rejected. I tend to use allSettled() in most cases. return Q.allSettled(tableDefinitionGetters); }; function recordEntry (tableName){ return function(createTableQryResult){ self.backup += "DROP TABLE " + tableName + "\n\n"; self.backup += createTableQryResult[0][0]["Create Table"] + "\n\n"; }; }; function saveFile(){ // Q.denodeify return a promise-enabled version of a node-style function // the below is probably excessively terse with its immediate invocation return (Q.denodeify(require('fs').writeFile))(filename, self.backup); } // with the above all done, now you can actually make the magic happen, // starting with the promise-return Q.ninvoke to connect to the DB // note that the successive .then()s will be executed iff (if and only // if) the preceding item resolves successfully, .catch() will get // executed in the event of any upstream error, and finally() will // get executed no matter what. Q.ninvoke(this.connection, 'connect') .then(getTables) .then(doTableEntries) .then(saveFile) .then( function() {console.log('Success'); } ) .catch( function(err) {console.log('Something went awry', err); } ) .finally( function() {self.connection.destroy(); } ); }; var myConnection = { host : '127.0.0.1', user : 'root', password : 'root', database : 'test' }; // I have left this as constructor-based calling approach, but the // constructor just does it all so I just ignore the return value new MysqlBackup(myConnection,'./backup_test.txt');