.find() returning nothing even when data exists - mongodb

Question

I've a mongo database with 3 collections for 3 different kind of users as User,Partner,Admin. Whenever a new user of any type signup I'm searching all three collections to check if username and email exist already. I'm trying to achieve this by calling a function as:
function checkAttribute(attr,val,callback){
User.find({attr: val},function(err,user){
if(err){
console.log(err);
}else{
if(user.length === 0){
Partner.find({attr: val},function(err,partner){
if(err){
console.log(err);
}else{
if(partner.length === 0){
Admin.find({attr: val},function(err,admin){
if(err){
console.log(err);
}else{
if(admin.length === 0){
return callback(null,true);
}else{
return callback(null,false);
}
}
});
}else{
return callback(null,false);
}
}
});
}else{
return callback(null,false);
}
}
});
};
Calling function line:
checkAttribute("username",newUser.username,function(error,response){
.......
});
But this is not working as it returns true always even when users with passed username/email exists already. I am unable to find the problem. Any one knows why this is happening?
Thanks in advance.

Answer 1

Since you are passing in the attribute as a variable in the function parameters, the query document
{ attr: val } is an object with the key "attr", not the dynamic attribute you pass in.
To fix this, you need to use computed property names in your query object as
{ [attr]: val }
Also, the function can use async/await pattern to be more readable and for the purpose of finding if a document exist findOne does the job so
well as it returns a document if it exists and null otherwise.
So your function can be refactored as
async function checkAttribute(attr, val, callback) {
try {
const query = { [attr]: val }
const user = await User.findOne(query).exec()
const partner = await Partner.findOne(query).exec()
const admin = await Admin.findOne(query).exec()
const found = (user || partner || admin) ? true: false
return callback(null, found)
} catch (err) {
console.error(err)
return callback(err, null)
}
};

Answer 2

attr: in your queries will search for a db field called attr. If you want to use the function parameter attr, use [attr]: as the key.
Example:
attr = 'username'
User.find({ [attr]: val }, function (err, user) {
if (err) {
console.log(err);
}
})
This is a feature available since ES6 so should work fine. See the docs here for more info