Despite the user.length being greater than zero, the duplicate variable is always false. The console first prints 'false' and then shows the duplicate record.
var duplicate = false;
userModel.find({mobileNumber: 123456789}, (err, user) => {
if(user.length > 0){
console.log("Duplicate Record");
duplicate = true;
}
});
console.log(duplicate);
When working with Node JS, one must understand its asynchronous nature. This means that it will first print the content inside console.log(duplicate);, before executing the find function.
Make sure to check the logs for a better understanding:
var duplicate = false;
userModel.find({mobileNumber: 123456789},(err, user)=>{
console.log('find function called');
if(user.length > 0){
console.log("Duplicate Record");
duplicate = true;
console.log('duplicate inside',duplicate);
}
});
console.log('duplicate outside',duplicate);
The reason behind the false reading of duplicate is due to the timing issue where console.log executes before the MongoDB query's callback changes the value of duplicate.
To tackle this race condition, Mongoose provides the option to return a Promise for queries, enabling the use of async/await for achieving the synchronous behavior desired.
async () => {
var duplicate = false;
let users = await userModel.find({mobileNumber: 123456789}).exec();
if (users.length > 0) {
console.log("Duplicate record found");
duplicate = true;
}
console.log(duplicate); // outputs true
// additional code
}
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