Updating a nested field into an array using r.Branch

nestedArray.go

package main

import (
	"fmt"

	r "gopkg.in/dancannon/gorethink.v3"
)

type Commentary struct {
	From    string `gorethink:"from"`
	Recid   string `gorethink:"recid"`
	Subject string `gorethink:"subject"`
}

type Post struct {
	ID       string       `gorethink:"id,omitempty"`
	Comments []Commentary `gorethink:"comments"`
	Subject  string       `gorethink:"subject"`
	Author   string       `gorethink:"author"`
}

var initialPost = Post{
	Subject: "My name is Bob and it's the worst ever",
	Author:  "Bob",
	Comments: []Commentary{
		Commentary{From: "Hulk", Recid: "ddef-a341", Subject: "I'm hulk!"},
		Commentary{From: "Thor", Recid: "aced-a112", Subject: "I'm thor"},
	},
}

var editedCommmentary = Commentary{
	From:    "Hulk",
	Recid:   "ddef-a341",
	Subject: "I'm hulk! Arggggh!",
}

type term map[string]interface{}

func main() {
	session, err := r.Connect(r.ConnectOpts{
		Database: "test",
	})
	tablePosts := "posts"
	if err != nil {
		panic(err)
	}
	recID := editedCommmentary.Recid
	result, err := r.Table(tablePosts).Insert(initialPost).RunWrite(session)
	if err != nil {
		panic(err)
	}
	postID := initialPost.ID
	if len(result.GeneratedKeys) > 0 {
		postID = result.GeneratedKeys[0]
	}
	response, err := r.Table(tablePosts).Get(postID).Update(term{
		"comments": r.Row.Field("comments").Map(func(c r.Term) interface{} {
			return r.Branch(c.Field("recid").Eq(recID), editedCommmentary, c)
		}),
	}).RunWrite(session)
	if err != nil {
		panic(err)
	}
	fmt.Println(response)
	cursor, err := r.Table(tablePosts).Get(postID).Run(session)
	if err != nil {
		panic(err)
	}
	err = cursor.One(&initialPost)
	if err != nil {
		panic(err)
	}
	fmt.Println(initialPost)
}