mgo_pipeline_lookup.go

package main

import (
	"time"

	"fmt"

	"gopkg.in/mgo.v2"
	"gopkg.in/mgo.v2/bson"
)

type SuiteGroup struct {
	ID      *bson.ObjectId `bson:"_id,omitempty" json:"_id"`
	Name    *string        `bson:"name,omitempty" json:"name,omitempty"`
	SuiteID *bson.ObjectId `bson:"_suiteId" json:"_suiteId"`
	Kind    *string        `bson:"kind,omitempty" json:"kind,omitempty"`

	// pipeline get, Suites []Suite
	Suite []Suite `bson:"suite" json:"suites"`
}

type Suite struct {
	ID      *bson.ObjectId `bson:"_id" json:"_id,omitempty"`
	Created *time.Time     `bson:"created,omitempty" json:"created,omitempty"`
}

// See also
// https://docs.mongodb.com/manual/aggregation/
// https://docs.mongodb.com/manual/core/aggregation-pipeline/
// https://github.com/go-mgo/mgo/issues/248

func main() {
	session, err := mgo.Dial("127.0.0.1")
	if err != nil {
		panic(err)
	}

	defer session.Close()

	// Optional. Switch the session to a monotonic behavior.
	session.SetMode(mgo.Monotonic, true)

	c := session.DB("test").C("suitegroups")

	pipeline := []bson.M{
		bson.M{"$match": bson.M{"name": "Admin"}},
		bson.M{"$lookup": bson.M{"from": "suites", "localField": "_suiteId", "foreignField": "_id", "as": "suite"}},
	}

	var resp SuiteGroup
	c.Pipe(pipeline).One(&resp)

	fmt.Printf("SuiteID [%s] SuiteObj %#v\n", resp.SuiteID.String(), resp.Suite[0])
}