Aggregation Expression - $first

Function Build

Build $first with the First function from the aggregation package.

// bson.D{bson.E{Key:"firstName", Value:bson.D{bson.E{Key:"$first", Value:"$name"}}}}
result := aggregation.First("firstName", "$name")

Method Build (Builder)

Build $first with the First method from aggregation.NewBuilder().

// bson.D{bson.E{Key:"firstName", Value:bson.D{bson.E{Key:"$first", Value:"$name"}}}}
result := aggregation.NewBuilder().
    First("firstName", "$name").
    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.

FirstWithoutKey

Function build:

// bson.D{bson.E{Key:"$first", Value:"$name"}}
expr := aggregation.FirstWithoutKey("$name")

Method build (Builder):

// bson.D{bson.E{Key:"$first", Value:"$name"}}
expr := aggregation.NewBuilder().
    FirstWithoutKey("$name").
    Build()