$multiply (aggregation)

Definition

$multiply

Multiplies numbers together and returns the result. Pass the arguments to $multiply in an array.

The $multiply expression has the following syntax:

{ $multiply: [ <expression1>, <expression2>, ... ] }

The arguments can be any valid expression as long as they resolve to numbers. For more information on expressions, see Expression Operators.

Starting in MongoDB 6.1 you can optimize the $multiply operation. To improve performance, group references at the end of the argument list. For example,

$multiply: [ 1, 2, 3, '$a', '$b', '$c' ]

Example

Consider a sales collection with the following documents:

{ "_id" : 1, "item" : "abc", "price" : 10, "quantity": 2, date: ISODate("2014-03-01T08:00:00Z") }
{ "_id" : 2, "item" : "jkl", "price" : 20, "quantity": 1, date: ISODate("2014-03-01T09:00:00Z") }
{ "_id" : 3, "item" : "xyz", "price" : 5, "quantity": 10, date: ISODate("2014-03-15T09:00:00Z") }

The following aggregation uses the $multiply expression in the $project pipeline to multiply the price and the quantity fields:

db.sales.aggregate(
   [
     { $project: { date: 1, item: 1, total: { $multiply: [ "$price", "$quantity" ] } } }
   ]
)

The operation returns the following results:

{ "_id" : 1, "item" : "abc", "date" : ISODate("2014-03-01T08:00:00Z"), "total" : 20 }
{ "_id" : 2, "item" : "jkl", "date" : ISODate("2014-03-01T09:00:00Z"), "total" : 20 }
{ "_id" : 3, "item" : "xyz", "date" : ISODate("2014-03-15T09:00:00Z"), "total" : 50 }