Efficient search of substrings in MongoDB - node.js

Question

I want to search in a User collection for a document containing a given username while the user is typing in the username. For example:
Database:
happyuser
happyuser2
happy_user
userhappy
User types in "hap", all usernames should be found, since "hap" is included in all of them. When I do the following, only results are found, when the full username is provided and non of the results is found for the query "hap":
User.find(
{
$text: {
$search: "hap",
$diacriticSensitive: true
}
},
{
score: {
$meta: "textScore"
}
}, function(err, results) {
if (err) {
next(err);
return;
}
return res.json(results);
});
I only get results, when I search by providing a regular expression:
User.find({
"username": new RegExp("hap")
}).exec(function(err, results) {
if (err) {
next(err);
return;
}
return res.json(results);
});
But this cannot be efficient, right? I mean, with a regular expression MongoDB basically touches all documents in the user collection or am I wrong? What is the best practice solution for such a search query?

Answer 1

Searching using regular expression is pretty efficient (at least for sql) unless you have wide array of characters included in your search (complex-random search) that out-limits your databases (regex's) capabilities or unless you have too many databases to search from that it takes forever for your regex to find them all in reasonable time. Specifically for mongoDB, I usually go with:
>db.collection.find( { key: { $regex: 'P.*'} } ).pretty();
This command should give me all details about 'key' starting with letter 'P'. Some people also use %"Your-Expression-Here%. However, I would suggest above command to be more efficient. Have a look at documentation: https://docs.mongodb.com/manual/reference/method/db.collection.find/

Answer 2

In context of your example, you won't be able to perform plain text search.
The $text operator matches on the complete stemmed word. So if a
document field contains the word blueberry, a search on the term blue
will not match. However, blueberry or blueberries will match.
On the over hand, if you don't want to mess with regex. Give a try to where:
User.find().$where(function() {
return this.username.indexOf('hap') != -1;
});