dynamodb golang query one Item

golang  dynamodb  query  oneItem  and unmarshal  to object

// +build example

package main

import (
    //    "flag"
    "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"
    "os"
    "time"
)

func exitWithError(err error) {
    fmt.Fprintln(os.Stderr, err)
    os.Exit()
}

func main() {
    cfg := Config{}
    if err := cfg.Load(); err != nil {
        exitWithError(fmt.Errorf("failed to load config, %v", err))
    }

    // Create the config specifiing the Region for the DynamoDB table.
    // If Config.Region is not set the region must come from the shared
    // config or AWS_REGION environment variable.
    awscfg := &aws.Config{}
    if len(cfg.Region) >  {
        awscfg.WithRegion(cfg.Region)
    }

    // Create the session that the DynamoDB service will use.
    sess, err := session.NewSession(awscfg)
    if err != nil {
        exitWithError(fmt.Errorf("failed to create session, %v", err))
    }

    // Create the DynamoDB service client to make the query request with.
    svc := dynamodb.New(sess)

    // Build the query input parameters
    params := &dynamodb.ScanInput{
        TableName: aws.String(cfg.Table),
    }
    if cfg.Limit >  {
        params.Limit = aws.Int64(cfg.Limit)
    }
    fmt.Println("params is: ", params)
    // Make the DynamoDB Query API call
    result, err := svc.Scan(params)
    if err != nil {
        exitWithError(fmt.Errorf("failed to make Query API call, %v", err))
    }

    items := []Item{}

    // Unmarshal the Items field in the result value to the Item Go type.
    err = dynamodbattribute.UnmarshalListOfMaps(result.Items, &items)
    if err != nil {
        exitWithError(fmt.Errorf("failed to unmarshal Query result items, %v", err))
    }

    // Print out the items returned
    for i, item := range items {
        fmt.Printf("%d:  UserID: %d, Time: %s Msg: %s  Count: %d SecretKey:%s DeviceId: %s CampaginId:%s \n     ", i, item.UserID, item.Time, item.Msg, item.Count, item.SecretKey, item.DeviceId, item.CampaginId)
        //fmt.Printf("\tNum Data Values: %d\n", len(item.Data))
    }

    /*    //1231241  deviceid
        params_del := &dynamodb.ScanInput{
            TableName: aws.String(cfg.Table),

        }
    */
    //query oneItem  demo
    params_get := &dynamodb.GetItemInput{
        Key: map[string]*dynamodb.AttributeValue{
            "deviceid": {
                S: aws.String(""),
            },
        },
        TableName: aws.String(cfg.Table), // Required
    }

    resp, err_get := svc.GetItem(params_get)
    oneItem := Item{}
    if err_get == nil {
        // resp is now filled
        fmt.Printf("resp type is %T \n ", resp.Item)
        err = dynamodbattribute.UnmarshalMap(resp.Item, &oneItem)
        if err == nil {
            fmt.Printf("  UserID: %d, Time: %s Msg: %s  Count: %d SecretKey:%s DeviceId: %s CampaginId:%s \n     ", oneItem.UserID, oneItem.Time, oneItem.Msg, oneItem.Count, oneItem.SecretKey, oneItem.DeviceId, oneItem.CampaginId)
        } else {
            fmt.Println(" Unmarshal err :", err)
        }
        //fmt.Println("convert to Struct obj  err is ", err, "oneItem is:", oneItem)
    } else {
        fmt.Println("GetItem err is: ", err_get)
    }

}

type Item struct {
    UserID     int       // Hash key, a.k.a. partition key
    Time       time.Time // Range key, a.k.a. sort ke
    Msg        string    `dynamo:"Message"`
    Count      int       `dynamo:",omitempty"`
    SecretKey  string    `dynamo:"-"` // Ignored
    DeviceId   string    `dynamo:"deviceid"`
    CampaginId string    `dynamo:"campid"`
}

type Config struct {
    Table  string // required
    Region string // optional
    Limit  int64  // optional

}

func (c *Config) Load() error {
    //flag.Int64Var(&c.Limit, "limit", 0, "Limit is the max items to be returned, 0 is no limit")
    //flag.StringVar(&c.Table, "table", "", "Table to Query on")
    //flag.StringVar(&c.Region, "region", "", "AWS Region the table is in")
    //flag.Parse()
    c.Limit =
    c.Region = "ap-southeast-1"
    c.Table = "xxx_your_table_name"
    if len(c.Table) ==  {
        //    flag.PrintDefaults()
        return fmt.Errorf("table name is required.")
    }

    return nil
}