Question

I have a MongoDB database with documents that look like this:

{"users" : ["u1", "u2", "u3"]}
{"users" : ["u1", "u4"]}
{"users" : ["u1", "u3", "u5", "u6", "u7"]}

I would like to obtain the count of the document with the larger number of users. Using the above, the query would return 5 as the highest user count within the database. How can I do this in MongoDB?

I can get the number of documents with a specific size with:

db.mydb.find({users: {$size: 5}}).count()

However, I can not figure out how to find the largest count within all the documents in the user array.

Thanks.

Answer 1

You can’t do this directly in MongoDB. However, what you can do is have an extra field in the same document called “user_count” and use the $inc operator to increment it by one every time you add a new user to the “users” array.

Your update would look something like:

db.mydb.update({<update_condition>}, {$push :{"users":"u8"}, $inc : {"user_count":1}})