$not (aggregation)

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Definition

Behavior
Example

MongoDB 5.0 is end of life as of October 2024. This version of the documentation is no longer supported. To upgrade your 5.0 deployment, see the MongoDB 6.0 upgrade procedures.

Definition

$not

Evaluates a boolean and returns the opposite boolean value; i.e. when passed an expression that evaluates to true, $not returns false; when passed an expression that evaluates to false, $not returns true.

$not has the following syntax:

{ $not: [ <expression> ] }

For more information on expressions, see Expressions.

Behavior

In addition to the false boolean value, $not evaluates as false the following: null, 0, and undefined values. The $not evaluates all other values as true, including non-zero numeric values and arrays.

Example	Result
`{ $not: [ true ] }`	`false`
`{ $not: [ [ false ] ] }`	`false`
`{ $not: [ false ] }`	`true`
`{ $not: [ null ] }`	`true`
`{ $not: [ 0 ] }`	`true`

Example

Consider an inventory collection with the following documents:

{ "_id" : 1, "item" : "abc1", description: "product 1", qty: 300 }
{ "_id" : 2, "item" : "abc2", description: "product 2", qty: 200 }
{ "_id" : 3, "item" : "xyz1", description: "product 3", qty: 250 }
{ "_id" : 4, "item" : "VWZ1", description: "product 4", qty: 300 }
{ "_id" : 5, "item" : "VWZ2", description: "product 5", qty: 180 }

The following operation uses the $not operator to determine if qty is not greater than 250:

db.inventory.aggregate(
   [
     {
       $project:
          {
            item: 1,
            result: { $not: [ { $gt: [ "$qty", 250 ] } ] }
          }
     }
   ]
)

The operation returns the following results:

{ "_id" : 1, "item" : "abc1", "result" : false }
{ "_id" : 2, "item" : "abc2", "result" : true }
{ "_id" : 3, "item" : "xyz1", "result" : true }
{ "_id" : 4, "item" : "VWZ1", "result" : false }
{ "_id" : 5, "item" : "VWZ2", "result" : true }

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$ne

$objectToArray