JSON pipeline stages

main.go

package main

import (
	"context"
	"fmt"

	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/mongo"
	"go.mongodb.org/mongo-driver/mongo/options"
)

func main() {
	geoNearStage := `
	{
		"$geoNear": {
			"includeLocs": "location",
			"distanceField": "distance",
			"maxDistance": 1000,
			"spherical": true,
			"near": {
				"type": "Point",
				"coordinates": [10, 10]
			}
		}
	}`
	countStage := `
	{
		"$count": "number"
	}`

	ctx := context.TODO()
	uri := "mongodb://localhost:27017"
	opts := options.Client().ApplyURI(uri)

	client, err := mongo.Connect(ctx, opts)
	if err != nil {
		panic(err)
	}
	defer client.Disconnect(ctx)

	coll := client.Database("foo").Collection("bar")
	pipeline := buildPipeline(geoNearStage, countStage)
	cursor, err := coll.Aggregate(ctx, pipeline)
	if err != nil {
		panic(err)
	}
	defer cursor.Close(ctx)

	for cursor.Next(ctx) {
		fmt.Println(cursor.Current)
	}
}

func buildPipeline(stages ...string) mongo.Pipeline {
	var pipeline mongo.Pipeline
	for idx, stage := range stages {
		var stageDoc bson.D
		if err := bson.UnmarshalExtJSON([]byte(stage), false, &stageDoc); err != nil {
			panic(fmt.Sprintf("error unmarshalling stage %d: %v", idx, err))
		}

		pipeline = append(pipeline, stageDoc)
	}

	return pipeline
}