$lt (aggregation)

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Definition

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

$lt

Compares two values and returns:

true when the first value is less than the second value.
false when the first value is greater than or equivalent to the second value.

The $lt compares both value and type, using the specified BSON comparison order for values of different types.

$lt has the following syntax:

{ $lt: [ <expression1>, <expression2> ] }

For more information on expressions, see Expressions.

Example

Consider an inventory collection with the following documents:

db.inventory.insertMany( [
   { _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 $lt operator to determine if qty is less than 250:

db.inventory.aggregate(
   [
     {
       $project:
          {
            item: 1,
            qty: 1,
            qtyLt250: { $lt: [ "$qty", 250 ] },
            _id: 0
          }
     }
   ]
)

The operation returns the following results:

{ "item" : "abc1", "qty" : 300, "qtyLt250" : false }
{ "item" : "abc2", "qty" : 200, "qtyLt250" : true }
{ "item" : "xyz1", "qty" : 250, "qtyLt250" : false }
{ "item" : "VWZ1", "qty" : 300, "qtyLt250" : false }
{ "item" : "VWZ2", "qty" : 180, "qtyLt250" : true }

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