使用事务在 Go (Google App Engine) 中执行并发安全更新

package main

import (
    "context"
    "fmt"
    "log"
    "time"

    "google.golang.org/appengine/datastore"
    "google.golang.org/appengine/v2/aetest"
)

// Account 实体结构
type Account struct {
    Balance   int64     `datastore:"Balance"`
    Rate      int64     `datastore:"Rate"`
    CheckDate time.Time `datastore:"CheckDate"`
}

func main() {
    ctx := context.Background()

    // 创建一个 App Engine 测试实例
    inst, err := aetest.NewInstance(nil)
    if err != nil {
        log.Fatalf("Failed to create App Engine instance: %v", err)
    }
    defer inst.Close()

    // 创建一个请求
    req, err := inst.NewRequest("GET", "/", nil)
    if err != nil {
        log.Fatalf("Failed to create request: %v", err)
    }

    // 获取 App Engine 上下文
    ctx = aetest.NewContext(req)
    defer ctx.Done()

    // 账户Key
    accountKey := datastore.NewKey(ctx, "Account", "user1", 0, nil)

    // 定义更新账户余额的函数
    updateAccountBalance := func(ctx context.Context) error {
        var account Account

        // 1. 读取实体
        err := datastore.Get(ctx, accountKey, &account)
        if err != nil {
            return err
        }

        // 2. 计算自上次检查以来的时间差
        seconds := time.Since(account.CheckDate).Seconds()

        // 3. 更新余额
        account.Balance += int64(float64(account.Rate) * seconds)
        account.CheckDate = time.Now()

        // 4. 保存实体
        _, err = datastore.Put(ctx, accountKey, &account)
        return err
    }

    // 使用事务执行更新操作
    err = datastore.RunInTransaction(ctx, updateAccountBalance, nil)
    if err != nil {
        log.Fatalf("Transaction failed: %v", err)
    }

    fmt.Println("Account balance updated successfully.")

    // 验证余额是否正确更新
    var updatedAccount Account
    err = datastore.Get(ctx, accountKey, &updatedAccount)
    if err != nil {
        log.Fatalf("Failed to get updated account: %v", err)
    }

    fmt.Printf("Updated balance: %d\n", updatedAccount.Balance)
    fmt.Printf("Updated CheckDate: %v\n", updatedAccount.CheckDate)
}