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