Mongodb sorting order

Question

Is there a way to specify the order of keys to sort by?

There seems to be some confusion in the comments. To be clear, I'm not asking about ascending or descending order. I'm asking if I can specify sorting priority.

For example, I want to sort by:

• pinned (Boolean)
• score (Number)
• newest (Date or ObjectId)

so that

• only docs with the same pinned value get sorted by score, and
• only docs with the same pinned and score get sorted by newest?

In other words,

• score, newest should never be considered if pinned value is different (just sort by pinned)
• newest should never be considered if score is different.

For example,

{ pinned: false, score:1, _id: new }
{ pinned: true, score:1, _id: oldest }
{ pinned: false, score:2, _id: old }

should be ordered as

{ pinned: true,  score: 1, _id: oldest }
{ pinned: false, score: 1, _id: new }
{ pinned: false, score: 2, _id: old }

Answer 1

While JSON documents are unordered, in MongoDB there are several places where order matters. The most important ones to remember are:

• sort order
• index specification order

When you specify a sort, the sort order will follow the order of fields, so in your case it would be .sort({pinned:1,score:1,newest:1}) you can see an example in the documentation.

Some operations expect fields in particular order.

It also matters for subdocuments if you are trying to match them (whereas top level field order in the query does not matter).

Answer 2

So I inserted some sample data as is in your question with mongo shell:

db.test.insert({ pinned: false, score:1, _id: "new" });
db.test.insert({ pinned: true, score:1, _id: "oldest" });
db.test.insert({ pinned: false, score:2, _id: "old" });

Try to sort it by:

db.test.find().sort({pinned: -1, score: 1, _id: 1})

It turns out the result is:

{ "_id" : "oldest", "pinned" : true, "score" : 1 }
{ "_id" : "new", "pinned" : false, "score" : 1 }
{ "_id" : "old", "pinned" : false, "score" : 2 }

Isn't that what you want?

EDIT: Keep in mind that JavaScript doesn't strictly obey JSON spec. e.g. JSON spec also says property names should quoted with ", JavaScript however you don't have to quote, or you can quote with '.