How do i get success count for successful insertion of students? - asynchronous

Question

function bulkinsertion(req,res){
var i;
var student = req.body;
var successCount=0 , errorCount=0;
for(i=0;i<student.length;i++){
models.Student.create(student[i]).then(result =>{
successCount++;
}).catch(error =>{
errorCount++;
});
}
res.status(200).json({
message:"success",
successCount:successCount
})
console.log(successCount,errorCount);
}
Here I'm getting successCount is 0 after inserting multiple students also. Before the completion of insertion I'm getting JSON response so how should I get correct successCount and errorCount values? I need to wait for the completion of insertion then I have to get JSON response with successCount as no of students inserted to the table.

Answer 1

The issue seems to be that models.Student.create(...) is asynchronous which means that it will take some time to complete and the rest of your code will go on without waiting for it to complete. That's why you call .then() to tell it what to do when it's done. The issue is that you are sending your response before you ever finish creating any of the records.
Imagine if it takes 1 second to create each record. Your for loop will cycle through all of them almost instantly and start them all simultaneously. Then you will return before waiting for even one of them to complete.
To fix this, either mark your function async and then use the await keyword to wait for the update to be finished, or use Promise.all and more then() chains to handle everything.
For example:
async function bulkinsertion(req, res) {
let students = req.body;
let successCount = 0
let errorCount = 0;
// This will start all the creations simultaneously and then wait
// for all of them to complete before continuing
await Promise.all(
students
.forEach((student) => models.Student.create(student))
.then((result) => { successCount++; })
.catch((err) => { errorCount++; })
);
res.status(200).json({
message:"success",
successCount:successCount
})
console.log(successCount,errorCount);
}
Or, create the records one at a time by using await inside the loop:
async function bulkinsertion(req, res) {
let students = req.body;
let successCount = 0
let errorCount = 0;
for(i=0;i<student.length;i++){
// This will wait for each record to be created
// before going on to the next
try {
let result = await models.Student.create(student[i]);
successCount++;
} catch {
errorCount++;
}
}
res.status(200).json({
message:"success",
successCount:successCount
})
console.log(successCount,errorCount);
}