聚合表达式 - $map

函数构建

使用 aggregation 包提供的 Map 函数构建 $map。

// bson.D{bson.E{Key:"scoreLabels", Value:bson.D{bson.E{Key:"$map", Value:bson.D{bson.E{Key:"input", Value:"$scores"}, bson.E{Key:"as", Value:"score"}, bson.E{Key:"in", Value:bsonx.D("$toString", "$$score")}}}}}}
result := aggregation.Map("scoreLabels", "$scores", "score", bsonx.D("$toString", "$$score"))

方法构建（构建器）

使用 aggregation.NewBuilder() 的 Map 方法构建 $map。

// bson.D{bson.E{Key:"scoreLabels", Value:bson.D{bson.E{Key:"$map", Value:bson.D{bson.E{Key:"input", Value:"$scores"}, bson.E{Key:"as", Value:"score"}, bson.E{Key:"in", Value:bsonx.D("$toString", "$$score")}}}}}}
result := aggregation.NewBuilder().
    Map("scoreLabels", "$scores", "score", bsonx.D("$toString", "$$score")).
    Build()

无字段名构建

当表达式需要作为另一个表达式的参数时，可以使用 WithoutKey 变体构建不带输出字段名的表达式片段。

MapWithoutKey

函数构建：

// bson.D{bson.E{Key:"$map", Value:bson.D{bson.E{Key:"input", Value:"$scores"}, bson.E{Key:"as", Value:"score"}, bson.E{Key:"in", Value:bsonx.D("$toString", "$$score")}}}}
expr := aggregation.MapWithoutKey("$scores", "score", bsonx.D("$toString", "$$score"))

方法构建（构建器）：

// bson.D{bson.E{Key:"$map", Value:bson.D{bson.E{Key:"input", Value:"$scores"}, bson.E{Key:"as", Value:"score"}, bson.E{Key:"in", Value:bsonx.D("$toString", "$$score")}}}}
expr := aggregation.NewBuilder().
    MapWithoutKey("$scores", "score", bsonx.D("$toString", "$$score")).
    Build()