DynamoDB Tutorial Part 3 (Update an Item conditionally)

main.go

package main

import (
	"fmt"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/dynamodb"
	"github.com/aws/aws-sdk-go/service/dynamodb/dynamodbattribute"
)

func main() {

	type MovieKey struct {
		Year  int    `json:"year"`
		Title string `json:"title"`
	}

	type MovieActorsCondition struct {
		Actors int `json:":num"`
	}

	type MovieInfo struct {
		Actors []string `json:"actors"`
	}

	type MovieInfoUpdated struct {
		Info MovieInfo
	}

	config := &aws.Config{
		Region:   aws.String("us-west-2"),
		Endpoint: aws.String("http://localhost:8000"),
	}

	sess := session.Must(session.NewSession(config))

	svc := dynamodb.New(sess)

	key, err := dynamodbattribute.MarshalMap(MovieKey{
		Year:  2015,
		Title: "The Big New Movie",
	})

	if err != nil {
		fmt.Println(err.Error())
		return
	}

	condition, err := dynamodbattribute.MarshalMap(MovieActorsCondition{
		Actors: 3,
	})

	if err != nil {
		fmt.Println(err.Error())
		return
	}

	input := &dynamodb.UpdateItemInput{
		Key:                       key,
		TableName:                 aws.String("Movies"),
		UpdateExpression:          aws.String("remove info.actors[0]"),
		ConditionExpression:       aws.String("size(info.actors) >= :num"),
		ExpressionAttributeValues: condition,
		ReturnValues:              aws.String("UPDATED_NEW"),
	}

	result, err := svc.UpdateItem(input)
	if err != nil {
		fmt.Println(err.Error())
		return
	}

	updatedAttributes := MovieInfoUpdated{}
	err = dynamodbattribute.UnmarshalMap(result.Attributes, &updatedAttributes)
	if err != nil {
		fmt.Println(err.Error())
		return
	}

	fmt.Println("Actors updated: ", updatedAttributes.Info.Actors)
}