Attempting to index and query a set of dynamic attributes, I seem to have encountered a bug.

> db.foo.save({attrs: [

{n: "low", v: 100}

,

{n: "high", v: 100}

]})
> db.foo.save({attrs: [

{n: "low", v: 200}

,

{n: "high", v: 500}

]})
> db.foo.find(

{"attrs.n": "low", "attrs.v": 500}

)
{ "_id" : ObjectId("4d66b232d6eb5559fa645ce2"), "attrs" : [

{ "n" : "low", "v" : 200 }

,

{ "n" : "high", "v" : 500 }

] }

Now we add an index, and this returns nothing:

> db.foo.ensureIndex(

{"attrs.n": 1, "attrs.v": 1}

)
> db.foo.find(

{"attrs.n": "low", "attrs.v": 500}

)
(Returns nothing)

Shouldn't the behavior be the same with the index in place?

However. A query matching a complete object with the document work with the index:
> db.foo.find(

{"attrs.n": "low", "attrs.v": 200}

)
{ "_id" : ObjectId("4d66b232d6eb5559fa645ce2"), "attrs" : [

{ "n" : "low", "v" : 200 }

,

{ "n" : "high", "v" : 500 }

] }

And seems to be doing the equivalent of an $elemMatch:
> db.foo.find({attrs: {$elemMatch:

{n: "low", v: 100}

}})
{ "_id" : ObjectId("4d66b227d6eb5559fa645ce1"), "attrs" : [

{ "n" : "low", "v" : 100 }

,

{ "n" : "high", "v" : 100 }

] }

Is this the expected behavior?