related to https://discuss.dgraph.io/t/unexpected-bahaviour-when-mutating-1-to-1-relations/5180

1_1test.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"

	"github.com/dgraph-io/dgo/v2"
	"github.com/dgraph-io/dgo/v2/protos/api"
	"google.golang.org/grpc"
)

type Node struct {
	UID  string `json:"uid"`
	Type string `json:"dgraph.type"`

	Name  string `json:"name"`
	Child *Node  `json:"child"`
}

type CancelFunc func()

func main() {
	dg, cancel := getDgraphClient()
	defer cancel()

	op := &api.Operation{}
	op.Schema = `
	type Node {
		name: string
		child: uid
	  }
	  
	  name: string .
	  child: uid .
	`

	ctx := context.Background()
	if err := dg.Alter(ctx, op); err != nil {
		log.Fatal(err)
	}

	p := Node{
		UID:  "_:parent",
		Type: "Node",
		Name: "parent",
		Child: &Node{
			UID:  "_:child",
			Type: "Node",
			Name: "child",
		},
	}

	mu := &api.Mutation{
		CommitNow: true,
	}
	pb, err := json.Marshal(p)
	if err != nil {
		log.Fatal(err)
	}

	mu.SetJson = pb
	assigned, err := dg.NewTxn().Mutate(ctx, mu)
	if err != nil {
		log.Fatal(err)
	}

	// Get Uids
	parentUID := assigned.Uids["parent"]

	var q = fmt.Sprintf(`query {
		data(func: uid(%s)) {
		  uid #parentUID
		  name
		  child {
			uid
			name
		  }
		}
	  }`, parentUID)

	respf, err := dg.NewTxn().Query(ctx, q)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println()
	fmt.Println(string(respf.Json))

	mu2 := &api.Mutation{
		CommitNow: true,
	}

	q1 := `
	{
	  me(func: eq(email, "[email protected]")) {
		v as uid
	  }
	}`

	update := Node{
		UID:  parentUID,
		Type: "Node",
		Child: &Node{
			UID:  "_:child",
			Type: "Node",
			Name: "child replacement",
		},
	}

	pb2, err := json.Marshal(update)
	if err != nil {
		log.Fatal(err)
	}

	mu2.SetJson = pb2
	assigned2, err := dg.NewTxn().Mutate(ctx, mu2)
	if err != nil {
		log.Fatal(err)
	}

	// Get Uids
	UID := assigned2.Uids["parent"]

	var q2 = fmt.Sprintf(`query {
		data(func: uid(%s)) {
		  uid
		  name
		  child {
			uid
			name
		  }
		}
	  }`, UID)

	respf2, err := dg.NewTxn().Query(ctx, q2)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println()
	fmt.Println(string(respf2.Json))

}

func getDgraphClient() (*dgo.Dgraph, CancelFunc) {
	conn, err := grpc.Dial("localhost:9080", grpc.WithInsecure())
	if err != nil {
		log.Fatal("While trying to dial gRPC")
	}

	dc := api.NewDgraphClient(conn)
	dg := dgo.NewDgraphClient(dc)

	return dg, func() {
		if err := conn.Close(); err != nil {
			log.Printf("Error while closing connection:%v", err)
		}
	}
}