Type Bracketing in Query Predicates

Which Operators Type Bracket

The inequality operators ($gt, $gte, $lt, and $lte) use type bracketing.

Negations ($ne and $nin) do not use type bracketing. They match values of any type. For example, { a: { $ne: 2 } } also matches documents where a is a string or an object, in addition to the numeric type in the comparison.

Type Bracketing for Comparisons to Numbers

BSON has several numeric types: int, long, double, and decimal. MongoDB treats these as equivalent for comparison, so a comparison against a number matches values of any numeric type.

For example, { a: { $gt: 0 } } matches a values of type int, long, double, or decimal.

Type Bracketing and Implicit Array Traversal

Type bracketing also applies when a comparison traverses an array implicitly. If the target field is an array, the comparison matches documents where at least one element satisfies the comparison and is of the same type as the operand.

For example, { a: { $gt: 3 } } matches { a: [ 1, 2, 3, 4 ] } and { a: [ "red", 4, "blue" ] }, but not { a: [ "red", "blue" ] }.

Example

Consider the following collection:

{ "_id": "apples", "qty": 5 }
{ "_id": "bananas", "qty": 7 }
{ "_id": "apricots", "qty": 3 }
{ "_id": "oranges", "qty": { "in stock": 8, "ordered": 12 } }
{ "_id": "avocados", "qty": "fourteen" }

The following query uses $gt to return documents where the value of qty is greater than 4:

db.inventory.find( { qty: { $gt: 4 } } )

[
  {
    _id: 'apples',
    qty: 5
  },
  {
    _id: 'bananas',
    qty: 7
  }
]

The document with _id equal to "apricots" is not returned because its qty value, 3, is not greater than 4.

The document with _id equal to "avocados" is not returned because its qty value is of type string while the $gt operand is of type integer.

The document with _id equal to "oranges" is not returned because its qty value is of type object.