forEach Loop not returning Array - mysql

Question

So, i seem to be having a problem with returning a value from my forEach MYSQL query loop in Node JS and then inserting this into an ejs template. Currently, these are my pieces of code:
app.js GET Request
app.get("/admin/stock", function(req, res) {
db.query("SELECT * FROM stock", function (err, stock) {
if (err) {
console.log("Error with showing SQL")
} else {
stock.forEach(function (stock) {
db.query("SELECT * FROM product WHERE productID = " +
stock.stock_productID, function (err, product) {
if (err) {
console.log("Error");
}
else {
stock.stock_productID = product[0].productName
}
});
db.query("SELECT * FROM currency WHERE currencyID = " +
stock.stock_currencyID, function (err, currency) {
if (err) {
console.log("Error");
}
else {
stock.stock_currencyID = currency[0].currencyName
}
});
db.query("SELECT * FROM customer WHERE customerID = " +
stock.stock_customerID, function (err, customer) {
if (err) {
console.log("Error");
}
else {
stock.stock_customerID =
customer[0].customerBusiness;
console.log(stock);
}
})
});
}
console.log(stock);
res.render("admin/stock", {stock:stock, userFName: req.user[1]})
})
});
Stock Page EJS
<table class="generalTable">
<tr>
<th>Product Name</th>
<th>Quantity</th>
<th>Currency</th>
<th>Cost</th>
<th>Date Bought</th>
<th>Bought From</th>
</tr>
<% stock.forEach(function(stock){ %>
<tr>
<td><%=stock.stock_productID%></td>
<td><%=stock.quantityStockCurrent%></td>
<td><%=stock.stock_currencyID%></td>
<td><%=stock.priceBought%></td>
<td><%=stock.boughtDate%></td>
<td><%=stock.stock_customerID%></td>
</tr>
<% }) %>
</table>
The First console.log of stock shows the replaced values, the second however, shows the original array values, and therefore the page is loaded in with the original values (IDs etc, instead of names).
How do I send the inner/edited array to the res.render instead of the original array?
Many Thanks,
Brad
EDIT//////
By using JOINs, the output was correct

Answer 1

I guess the database queries have not yet returned when you already render the stock object.
Remember, nodejs is asynchronous. You have to wait for all DB queries to come back before rendering the result.
I did have a similar problem when I first learned about nodejs: JavaScript nodejs mysql with queries in a loop

Answer 2

The problem is that javascript is asynchronous and that Javascript doesn't have a block scope, which means that you render file before the loop complete so you should use simple for loop for this.
you should replace your code with this :-
app.get("/admin/stock", function(req, res) {
db.query("SELECT * FROM stock", function (err, stocks) {
var stock = JSON.parse(JSON.stringify(stocks));
if (err) {
console.log("Error with showing SQL")
} else {
for(var i = 0 ; i< stock.length; i++) {
db.query("SELECT * FROM product WHERE productID = " +
stock[i].stock_productID, function (err, product) {
if (err) {
console.log("Error");
}
else {
stock[i].stock_productID = product[0].productName
}
});
db.query("SELECT * FROM currency WHERE currencyID = " +
stock[i].stock_currencyID, function (err, currency) {
if (err) {
console.log("Error");
}
else {
stock[i].stock_currencyID = currency[0].currencyName
}
});
db.query("SELECT * FROM customer WHERE customerID = " +
stock[i].stock_customerID, function (err, customer) {
if (err) {
console.log("Error");
}
else {
stock[i].stock_customerID =
customer[0].customerBusiness;
console.log(stock);
}
});
if(i === stock.length-1){
console.log(stock);
res.render("admin/stock", {stock:stock, userFName: req.user[1]})
}
};
}
})
});

Answer 3

You can use async.map for executing query in loop.
function getResults(id,cb){
db.query("SELECT * FROM product WHERE productID = " +
id.stock_productID, function (err, product) {
if (err) {
console.log("Error");
}
else {
id.stock_productID = product[0].productName
}
});
}
async.mapLimit(stock, 5, function(id, callback) {
getResults(id, function (err, res) {
if (err) return callback(err);
callback(null, res);
})
}, function(err, results) {
// results is an array of names
});