combining two $elemMatch queries with AND boolean operator in MongoDB

Question

I have two distinct mongoDB queries that represent two different conditions, for example:

{ stuff: { $elemMatch: { foo: 1, bar: "a" } } }

and:

{ stuff: { $elemMatch: { foo: 2, bar: "b" } } }

where stuff is an array of elements that have both foo and bar fields set.

Now, I am not sure how to match elements in the collection that meet at the same time the two aforementioned conditions.

Just to be clear: in this case I need to get all elements that have both one element of stuff that has foo set as 1 with bar set as "a" and also one element of stuff that has foo set as 2 with bar set as "b".

Doing { stuff: { $elemMatch: { foo: { $in: [1, 2] }, bar: { $in: ["a", "b"] } } } is wrong, since it will behave like an OR on the two expression (and including two new expressions).

Any idea on how to AND them?

Answer 1

Just to be clear: in this case I need to get all elements that have both one element of stuff that has foo set as 1 with bar set as "a" and also one element of stuff that has foo set as 2 with bar set as "b".

I hope I got it. Shouldn't that be

db.coll.find({ $and: [ 
                  { "stuff" : { $elemMatch : { "foo" : 1, "bar" : "a" } } },   
                  { "stuff" : { $elemMatch : { "foo" : 2, "bar" : "b" } } } ]});

?