Aggregation Expression - $concat

The source also provides Contact and ContactWithoutKey; they generate $concat as well.

Function Build

Build $concat with the Concat function from the aggregation package.

// bson.D{bson.E{Key:"fullName", Value:bson.D{bson.E{Key:"$concat", Value:[]interface {}{"$firstName", " ", "$lastName"}}}}}
result := aggregation.Concat("fullName", "$firstName", " ", "$lastName")

Method Build (Builder)

Build $concat with the Concat method from aggregation.NewBuilder().

// bson.D{bson.E{Key:"fullName", Value:bson.D{bson.E{Key:"$concat", Value:[]interface {}{"$firstName", " ", "$lastName"}}}}}
result := aggregation.NewBuilder().
    Concat("fullName", "$firstName", " ", "$lastName").
    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.

ConcatWithoutKey

Function build:

// bson.D{bson.E{Key:"$concat", Value:[]any{"$firstName", " ", "$lastName"}}}
expr := aggregation.ConcatWithoutKey("$firstName", " ", "$lastName")

Method build (Builder):

// bson.D{bson.E{Key:"$concat", Value:[]any{"$firstName", " ", "$lastName"}}}
expr := aggregation.NewBuilder().
    ConcatWithoutKey("$firstName", " ", "$lastName").
    Build()

ContactWithoutKey

Function build:

// bson.D{bson.E{Key:"$concat", Value:[]any{"$firstName", " ", "$lastName"}}}
expr := aggregation.ContactWithoutKey("$firstName", " ", "$lastName")

Method build (Builder):

// bson.D{bson.E{Key:"$concat", Value:[]any{"$firstName", " ", "$lastName"}}}
expr := aggregation.NewBuilder().
    ContactWithoutKey("$firstName", " ", "$lastName").
    Build()