Aggregation Expression - $sum

Function Build

Build $sum with the Sum function from the aggregation package.

// bson.D{bson.E{Key:"total", Value:bson.D{bson.E{Key:"$sum", Value:"$amount"}}}}
result := aggregation.Sum("total", "$amount")

Method Build (Builder)

Build $sum with the Sum method from aggregation.NewBuilder().

// bson.D{bson.E{Key:"total", Value:bson.D{bson.E{Key:"$sum", Value:"$amount"}}}}
result := aggregation.NewBuilder().
    Sum("total", "$amount").
    Build()

Build Without Key

When an expression needs to be passed as an argument to another expression, use a WithoutKey variant to build an expression fragment without an output field name.

SumWithoutKey

Function build:

// bson.D{bson.E{Key:"$sum", Value:"$amount"}}
expr := aggregation.SumWithoutKey("$amount")

Method build (Builder):

// bson.D{bson.E{Key:"$sum", Value:"$amount"}}
expr := aggregation.NewBuilder().
    SumWithoutKey("$amount").
    Build()