Is it possible to update value in the collection in the query? - node.js

Question

I am not sure whether the title explains what I try to say.
But here assume collection's structure is like;
[
{email: "alex#sda.com"},
{email: "elizabeth#sds.com"},
{email: "hannah#xx.com"},
]
I want to get emails but before the # character.
What have I done to achieve this?
db.collection.find({}).toArray(function(err, result){
var emails = [];
for(var i =0; i< result.length; i++){
emails.push(result[i].split("#")[0]);
}
})
But I don't find this efficient because after the query, I loop through the result and store them in new array.
Is there a better way to get only the alex, elizabeth, hannah parth with a query?
This is just an example. I want to ask your suggestions because I have lots of situations like this. (I am looking for a most efficient way to trim, update some values in the collections)

Answer 1

You can use the distinct method first to get the list of email addresses then use regex to get the names:
db.collection.distinct("email", function(err, result){
var emails = result.map(function(email){
return email.match(/^([^#]*)#/)[1];
});
console.log(emails);
});
With the aggregation framework, MongoDB 3.4 has a $split operator that you can use in conjunction with $arrayElemAt:
db.collection.aggregate([
{
"$group": {
"_id": null,
"emails": {
"$push": {
"$arrayElemAt": [
{ "$split": ["$email", "#"] },
0
]
}
}
}
}
], function(err, result){
if (err) throw err;
console.log(result);
/*
{
"_id" : null,
"emails" : [
"alex",
"elizabeth",
"hannah"
]
}
*/
});