Advanced querying operators
Operators start with a '$', so use single quotes!
Comparison:
$lt, $lte, $gt, $gte (<, <=, >, >=)
$ne (not equal)
Logical:
$or, $and
$nor (not or)
$not
Meta:
$exists (field exists)
$type (field type)
Evaluation:
$mod (modulo)
$where (JS expression)
Array:
$in (value needs to be one of the elements of the given array)
$nin (not in)
$all (value needs to match all elements of the given array)
$size (exact size of array)
$elemMatch (element in an array matches the specified match expression)