Wait for MySQL query execution in node,js - mysql

Question

I am using mysql in node.js. And there is a nested query in it. But it does not wait for inner query to complete. I don't understand call backs nd other function. My code is like.
exports._getItems=function(req,res){
let categoryId=req.query.categoryPost;
console.log(categoryId+"re")
con.query("SELECT item_id FROM shop_products where category_id =?",[categoryId], function (err, result, fields) {
if (err) throw res.status(403);
else
{
console.log("jhcsdcshd");
var parsedResult = JSON.parse(JSON.stringify(result));
let itemsData="";
for (var i = 0; i < parsedResult.length; i++)
{
let item_id=parsedResult[i].item_id;
console.log("Item_id is"+item_id)
con.query("SELECT id,modelNo FROM items where id =?",[item_id], function async(err1, result1, fields1,callback) {
if (err1) throw res.status(403);
else
{
var parsedResult1=JSON.parse(JSON.stringify(result1));
console.log(parsedResult1)
itemsData=itemsData+parsedResult1[0].id;
console.log("dddd"+itemsData);
if(i=parsedResult.length)
{
console.log("here");
console.log("Data"+itemsData)
res.status(200).send(itemsData);
}
}
});
console.log("ppppppp"+itemsData);
}
}
});
}
I just want that if anyone can tell me that exactly how i let do the wait for inner query execution according to my code . It is very appreciated if anyone can help me. Thanks

Answer 1

You can not call mysql query inside for loop you have to wait for execution. Here is your solutions
exports._getItems = function (req, res) {
let categoryId = req.query.categoryPost;
console.log(categoryId + "re")
con.query("SELECT item_id FROM shop_products where category_id =?", [categoryId], function (err, result, fields) {
if (err) throw res.status(403);
else {
console.log("jhcsdcshd");
var parsedResult = JSON.parse(JSON.stringify(result));
let itemsData = "";
var promises = [];
for (var i = 0; i < parsedResult.length; i++) {
let item_id = parsedResult[i].item_id;
console.log("Item_id is" + item_id);
promises.push(runQuery(con, item_id))
}
Promise.all(promises)
.then((data) => {
for (var i = 0; i < data.length; i++) {
var parsedResult1 = JSON.parse(JSON.stringify(data[i]));
console.log(parsedResult1)
itemsData = itemsData + parsedResult1[0].id;
console.log("dddd" + itemsData);
if (i = parsedResult.length) {
console.log("here");
console.log("Data" + itemsData)
res.status(200).send(itemsData);
}
}
})
.catch((error) => {
throw res.status(403);
})
}
})
}
function runQuery(con, item_id) {
return new Promise((resolve, reject) => {
con.query("SELECT id,modelNo FROM items where id =?", [item_id], function (err1, result1) {
if (err1) {
reject(err1);
} else {
resolve(JSON.parse(JSON.stringify(result1)));
}
})
});
}