Querying MongoDB to match in the first item in an array

Question

I'm aware of the $in operator, which appears to search for an item's presence in array, but I only want to find a match if the item is in the first position in an array.

For instance:

{     "_id" : ObjectId("0"),     "imgs" : [         "http://foo.jpg",         "http://bar.jpg",         "http://moo.jpg",         ] }, {     "_id" : ObjectId("1"),     "imgs" : [         "http://bar.jpg",         "http://foo.jpg",         "http://moo.jpg",         ] } 

I'm looking for a query akin to:

db.products.find({"imgs[0]": "http://foo.jpg"}) 

This would/should return the ObjectId("0") but not ObjectId("1"), as it's only checking against the first image in the array.

How can this be achieved? I'm aware I could just create a separate field which contains a single string for firstImg but that's not really what I'm after here.

Answer 1

I believe you want imgs.0. eg, given your example document, you want to say: db.products.find({"imgs.0": "http://foo.jpg"})

Be aware that referencing array indexes only works for the first-level array. Mongo doesn't support searching array indexes any deeper.