Go: Cloud Firestore のデータを読む (Read)

firestore_read.go

// ---------------------------------------------------------------
//	firestore_read.go
//
//					Dec/16/2020
//
// ---------------------------------------------------------------
package main
 
import (
	"context"
	"fmt"
	"log"
	"os"
	"strconv"
 
	firebase "firebase.google.com/go"
	"google.golang.org/api/iterator"
	"google.golang.org/api/option"
)
 
// ---------------------------------------------------------------
func main() {
	fmt.Fprintf (os.Stderr,"*** 開始 ***\n")
	// 初期化
	ctx := context.Background()
	sa := option.WithCredentialsFile("./application_default_credentials.json")
	app, err := firebase.NewApp(ctx, nil, sa)
	if err != nil {
		log.Fatalln(err)
	}
 
	client, err := app.Firestore(ctx)
	if err != nil {
		log.Fatalln(err)
	}
 
	// データ読み取り
	iter := client.Collection("cities").Documents(ctx)
	for {
		doc, err := iter.Next()
		if err == iterator.Done {
			break
		}
		if err != nil {
			log.Fatalf("Failed to iterate: %v", err)
		}
//		fmt.Println(doc.Ref.ID)
//		fmt.Println(doc.Data())
		fmt.Printf("%s\t",doc.Ref.ID)
		fmt.Printf("%s\t",doc.Data()["name"])
		population := doc.Data()["population"].(int64)
		str_population := strconv.FormatInt(population,10)
		fmt.Printf("%s\t",str_population)
		fmt.Println(doc.Data()["date_mod"])
	}
 
	// 切断
	defer client.Close()

	fmt.Fprintf (os.Stderr,"*** 終了 ***\n")
}

// ---------------------------------------------------------------

実行コマンド

```bash
project_id="project-dec16-2020"
echo $project_id
export GOOGLE_CLOUD_PROJECT=$project_id
#
go run firestore_read.go