insert data with node-mysql in loop
My code is as follows:
var mysql= require('mysql');
var client = mysql.createClient({
user: 'root',
password: 'root',
host: 'localhost'
});
client.query('USE sample');
for(var k=0;k<=100;k++)
{
var sql="SELECT `id` FROM `data` WHERE `id`= ?";
console.log(k);
client.query(sql,[k],function(err,results,field){
console.log("开发者_运维知识库DATABASE "+k);
if(results.length == 0) {
var sql2="INSERT INTO `data` (`id`) VALUES (?);";
client.query(sql2,[k],function(err,results,field){
});
}
});
}
client.end();
When I run this code , the results are as follows:
1
2
3
...
100
Database 101
Database 101
Database 101
...
Database 101
and it neither closes the database connection nor inserts any data.
I want to insert data in the loop. But before inserting the new record , it also needs to check whether it already exists or not.
The closure for the callback function binds to the variable k by reference, not by value. This means that by the time you execute the callbacks, they all get the latest k value (101). In order to bind to the current k value at the time of closure creation, you need to add a new variable scope. Perhaps something like this:
for(var k=0;k<=100;k++) {
var sql="SELECT `id` FROM `data` WHERE `id`= ?";
console.log(k);
(function () {
var kCopy = k;
client.query(sql,[kCopy],function(err,results,field){
console.log("DATABASE "+kCopy);
if(results.length == 0) {
var sql2="INSERT INTO `data` (`id`) VALUES (?);";
client.query(sql2,[kCopy],function(err,results,field){});
}
});
}());
}
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