[{_id:"Matches",update:[{import_created_at:166178442574}]},{_id:"Fails, has an extra field",update:[{import_created_at:166178442574,extra_field:123}]},{_id:"Fails, no matching value",update:[{import_created_at:0}]}]

db.collection.aggregate([{$match:{"update.import_created_at":{$in:[166178442574]}}}])