How to retrieve nested map values - go

Question

I want to scan AWS DynamoDB table and then pull only a certain value. Here is my code:
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"
)
func main() {
svc := dynamodb.New(session.New(), &aws.Config{Region: aws.String("us-west-2")})
params := &dynamodb.ScanInput{
TableName: aws.String("my_Dynamo_table_name"),
Limit: aws.Int64(2),
}
resp, err := svc.Scan(params)
if err != nil {
fmt.Println(err.Error())
return
}
fmt.Println(resp)
}
and The output is:
{
Count: 2,
Items: [{
update_time: {
N: "1466495096"
},
create_time: {
N: "1465655549"
}
},{
update_time: {
N: "1466503947"
},
create_time: {
N: "1466503947"
}
}],
LastEvaluatedKey: {
Prim_key: {
S: "1234567890"
}
},
ScannedCount: 2
}
Now, I want to retrieve the update_time value for all elements in above output. Here are my attempts:
for _, value := range resp.Items {
fmt.Println(value["create_time"]["N"])
}
and
for _, value := range resp.Items {
fmt.Println(value.create_time.N)
}
and
for _, value := range resp.Items {
fmt.Println(*value.create_time.N)
}
All above attempts error out with /var/tmp/dynamo.go:37: invalid operation: error.
I am from perl/python background and recently started learning golang.
How to retrieve nested map/array values in this case. Also, any reading references would be of great help. My google search did not reveal anything relevant.

Answer 1

The value of resp above is of the type *ScanOutput, which has Items type as []map[string]*AttributeValue.
To access update_time, you can try:
updateTimes := make([]string, 0)
// Items is a slice of map of type map[string]*AttributeValue
for _, m := range resp.Items {
// m is of type map[string]*AttributeValue
timeStrPtr := *m["update_time"].N
updateTimes = append(updateTimes, *timeStrPtr)
}
updateTimes should now contains all the "update_time" values as strings.
More details here.

Answer 2

You should use the dynamodbattribute package. it's cheaper, safer, and more readable.
Following your example:
type Row struct {
CreateTime int `dynamodbav:"create_time"`
UpdateTime int `dynamodbav:"update_time"`
}
// ...
rows := make([]*Row, len(resp.Items))
if err := dynamodbattribute.Unmarshal(resp.Items, &rows); err != nil {
// handle the error
}
// access the data
for _, row := range rows {
fmt.Println(row.CreateTime, row.UpdateTime)
}