How to filter in mongodb dynamically? - mongodb

Question

I am creating app that can filter data dynamically.
If i select "John", "US", and leave the sex as blank it will return no result because the query will search a sex that is blank. I can't figure out how can i dynamically filter that in the mongodb.
ex:
var fName="John",
fCountry="US",
fSex="";
db.users.find({ $and[ {sex: fSex}, {first_name: fName}, {country: fCountry} ]})
That query will return none.
I want the code to return a answer like this if i select "John", "US":
{"_id": <object>, "first_name": "John", "sex": "Male", "country": "US"}
users:
{"_id": <object>, "first_name": "John", "sex": "Male", "country": "US"},
{"_id": <object>, "first_name": "Rex", "sex": "Male", "country": "Mexico"},
{"_id": <object>, "first_name": "Jane", "sex": "Female", "country": "Canada"}
Thank You in advance!, btw i am new to mongo
Edited

Answer 1

You can build the query object instead of assuming it's going to looks like a specific structure.
You can add whatever checks you'd like.
var fName="John",
fCountry="US",
fSex="";
var query = { $and: [] };
if (fName !== "") { query.$and.push({name: fName}); }
if (fCountry !== "") { query.$and.push({country: fCountry}); }
if (fSex !== "") { query.$and.push({sex: fSex}); }
db.users.find(query);
Update:
As per #semicolon's comment, the $and here is unnecessary as mongo, by default, will "and" different fields together. A simpler solution reads:
var query = {};
...
query.name = fName; // et cetera.
I'll add that it may become necessary to use the key $and and other operators when building more elaborate queries.