Literal Operators

Operator	Description	Example
$literal	Allows the insertion of any literal value. This is used mainly when you'd like to use a value that would otherwise be evaluated as an expression.	pricesEqual: [{ $eq: [ "$cashValue", { $literal: "$10" } ] }]
$string	Allows the insertion of a string literal. The value must be a string or an expression that evaluates to a string.	[{"$concat": ["c_pants", {"$string": "c_pants"}] } -> "clown c_pants"
$number	Allows the insertion of a number value as a literal where a property name would otherwise be expected. The value must be a number or an expression that evaluates to a number.	[{"$add": ["c_scalar", {"$number": 1.23}] }]
$integer	Allows the insertion of an integer value as a literal where a property name would otherwise be expected. The value must be an integer or an expression that evaluates to an integer.	[{"$add": ["c_ints", {"$integer": 10}] }]
$boolean	Allows the insertion of a boolean value as a literal where a property name would otherwise be expected. The value must be a boolean or an expression that evaluates to a boolean.	[{"alwaysFirstName": {"$first": {"$cond": [{"$boolean": true}, "name.first", "name.last"]}}]
$date	Allows the insertion of a date value as a literal where a property name would otherwise be expected. The value must be a date or an expression that evaluates to a date.	[{"offsetDate": {"$add": [{"$date": "2015-06-07T14:48:00.000Z"}, "c_offset"]}]
$objectId	Allows the insertion of an objectId value as a literal where a property name would otherwise be expected. The value must be an objectId or an expression that evaluates to an objectId.	[{"$cmp": [{"$objectId": "561614700000000000000000"}, "_id"]}]
$array	Allows the insertion of an array value as a literal where a property name would otherwise be expected. The value must be an array or an expression that evaluates to an array.	[{"$setUnion": [{"$array": ["000000000000000000000007"]}, "roles"]}]
$object	Allows the insertion of an object value as a literal where a property name would otherwise be expected. The value must be an object or an expression that evaluates to an object.	[{"$eq": [{"$object": { "street": "Easy St" }}, "c_address"]}]