如何更快地在 MongoDB 中获得等效的 function？ WHERE 子句？

Question

i want to know how to query like MYSQL in java this function equivalent: SELECT nick FROM profiles WHERE uuid = 'something';

i have done something like that in my project but it seens too slow and its returning the whole document of the profile requested, unless i use document.get("nick") i get exactly what i want, i'm sorry but i'm really new to MongoDB and i haven't already founded something about this, everything that i found it doesn't really helped me so much..

this is the code:

FindIterable<Document> results = Main.getCollection(Main.getDatabase(plugin.database), plugin.collection).find(Document.parse("{ uid: '00000000-0000-0000-0009-01fbbfda08e8' }, { nick: 1 }")); 
           Document document = results.first();
           if(document.get("nick") != player.getName()) {
               System.out.println("do something");
           }

by document var from FindIterable it returns the whole document, but i just want to return the nick of that profile, which the uuid is "00000000-0000-0000-0009-01fbbfda08e8" so i dont need to use document.get and it will be much better for performance, if thats possible.. (sorry for bad english)

Answer 1

I suggest you to take a look at how indexes and covered queries work (projections), creating an index for a specific fields would improve your performance for those common queries, and projections would help you to get only the fields you need.

There are plenty of examples (in java also) https://docs.mongodb.com/manual/indexes/#covered-queries

Here there is an example of exactly what you are asking for: https://docs.mongodb.com/manual/tutorial/project-fields-from-query-results/

Field projection applied on your example:

.find(eq("uid", "00000000-0000-0000-0009-01fbbfda08e8")).projection(fields(include("nick"), excludeId()));