Javascript 节点mysql定时
我有这样一个递归查询(注意:这只是一个示例): 这不起作用,因为timmings都错了,代码不等待查询 我尝试过这样做:Javascript 节点mysql定时,javascript,mysql,node.js,timing,node-mysql,Javascript,Mysql,Node.js,Timing,Node Mysql,我有这样一个递归查询(注意:这只是一个示例): 这不起作用,因为timmings都错了,代码不等待查询 我尝试过这样做: var MyQuery = function(QueryString){ var Data; var Done = false; database.query(QueryString, function(err, result, fields) { Data = result; Done = true; });
var MyQuery = function(QueryString){
var Data;
var Done = false;
database.query(QueryString, function(err, result, fields) {
Data = result;
Done = true;
});
while(Done != true){};
return Data;
}
var user = function(data)
{
this.minions = [];
this.loadMinions = function()
{
_user = this;
result= MyQuery('select * from users where owner='+data.id);
for(var m in result)
{
_user.minions[result[m].id] = new user(result[m]);
_user.minions[result[m].id].loadMinions();
}
console.log("loaded all minions");
}
}
currentUser = new user(ID);
for (var m in currentUser.minions)
{
console.log("minion found!");
}
但是他只是僵住了,我是不是遗漏了什么?每个Node.js进程都是单线程的,所以
while(Done != true){};
接管线程,并且将Done
设置为true的回调永远不会运行,因为thead被无限循环阻塞
您需要重构程序,使依赖于查询结果的代码包含在回调本身中。例如,使MyQuery
接受回调参数:
MyQuery = function(QueryString, callback){
然后在
数据库的末尾调用回调。query
回调--甚至将其作为数据库提供。query
回调。由于节点是单线程的,因此冻结行为很不幸是正确的
您需要一个计划程序包来修复此问题。就我个人而言,我一直在用光纤来解决这类问题。您可能想看看这个或另一个promise库或async,解决问题的第一个障碍是理解Node.js中的I/O是异步的。一旦您知道这如何应用于您的问题,递归部分就会容易得多(特别是如果您使用像Async或Step这样的流控制库) 下面是一个示例,它完成了您尝试执行的一些操作(减去递归)。就我个人而言,我会避免递归加载可能未知数量/深度的记录;而是按需加载,如本例所示:
var User = function(data) {
this.data = data
this.minions;
};
User.prototype.getMinions = function(primaryCallback) {
var that = this; // scope handle
if(this.minions) { // bypass the db query if results cached
return primaryCallback(null, this.minions);
}
// Callback invoked by database.query when it has the records
var aCallback = function(error, results, fields) {
if(error) {
return primaryCallback(error);
}
// This is where you would put your recursive minion initialization
// The problem you are going to have is callback counting, using a library
// like async or step would make this party much much easier
that.minions = results; // bypass the db query after this
primaryCallback(null, results);
}
database.query('SELECT * FROM users WHERE owner = ' + data.id, aCallback);
};
var user = new User(someData);
user.getMinions(function(error, minions) {
if(error) {
throw error;
}
// Inside the function invoked by primaryCallback(...)
minions.forEach(function(minion) {
console.log('found this minion:', minion);
});
});
本例中需要注意的最大问题是回调。
database.query(…)
是异步的,您不希望占用事件循环等待它完成。通过向查询提供回调,aCallback
,可以解决这一问题,该回调在结果就绪时执行。一旦启动回调,在您对记录执行任何您想执行的处理之后,您就可以启动带有最终结果的primaryCallback
。您基本上错过了Node.js和您可能习惯于编程的环境之间记录最完整、最重要的变化。你是怎么做到的?
var User = function(data) {
this.data = data
this.minions;
};
User.prototype.getMinions = function(primaryCallback) {
var that = this; // scope handle
if(this.minions) { // bypass the db query if results cached
return primaryCallback(null, this.minions);
}
// Callback invoked by database.query when it has the records
var aCallback = function(error, results, fields) {
if(error) {
return primaryCallback(error);
}
// This is where you would put your recursive minion initialization
// The problem you are going to have is callback counting, using a library
// like async or step would make this party much much easier
that.minions = results; // bypass the db query after this
primaryCallback(null, results);
}
database.query('SELECT * FROM users WHERE owner = ' + data.id, aCallback);
};
var user = new User(someData);
user.getMinions(function(error, minions) {
if(error) {
throw error;
}
// Inside the function invoked by primaryCallback(...)
minions.forEach(function(minion) {
console.log('found this minion:', minion);
});
});