如何正确使用嵌套的 for 循环来遍历 golang 中的行？

Question

我正在尝试迭代嵌套循环，如下所示，但在第一个循环中声明的变量，如varOne, varTwo, varThree没有进入第二个循环

事实上，在for rowTwo:= range rowsTwo {

谁能指出我做错了什么或如何

func StudentScore() {

    var appendedScores []interface{}

    for rowOne := range rowsOne {
        varOne := rowOne.FirstName
        varTwo := rowOne.LastName
        varThree := rowOne.UserName

        req, _ := http.NewRequest("GET", fmt.Sprintf("https://example.com/users/%s/score", varThree), nil)
    
        client := &http.Client{}
        resp, _ := client.Do(req)


        type responseData struct {
            FirstName   string `json:"first_name"`
            LastName     string  `json:"last_name"`
            Score       float64 `json:"score"`

        }

        type StudentData struct {
            UserName   string `json:"username_name"`
            Score      float64 `json:"score"`
        }

        var rowsTwo []responseData
        
        respBody, _ := ioutil.ReadAll(resp.Body)
        err = json.Unmarshal(respBody, &rowsTwo) 
        fmt.Println("response: ", rowsTwo)
        
//         var appendedScores []interface{}
        studentData := &StudentData{}

        for rowTwo := range rowsTwo {

            fmt.Println("print vars from first loop: ", varOne, varTwo, varThree)
            fmt.Println("api response: ", resp)

            studentData.UserName=string(varThree)
            studentData.Score=float64(rowTwo.Score)

            appendedScores = append(appendedScores, *studentData)
        }

    }
    fmt.Println("student scores: ", appendedScores)

}

我要做的几乎是使用第一行范围内的行中的值并用于生成要在第二个 for 循环中使用的新值，以便我可以打印最终值。 所以 2 个嵌套 for 循环的唯一原因是因为我需要来自第一个 for 循环的值

有什么遗漏或更好的方法吗？

Answer 1

type StudentScore struct {
    UserName string  `json:"user_name"`
    Score    float64 `json:"score"`
}

func GetStudentScore() ([]StudentScore, error) {
    var scores []StudentScore

    for _, row := range rowsOne {
        s := StudentScore{UserName: row.UserName}

        // request score data
        resp, err := http.Get(fmt.Sprintf("https://example.com/users/%s/score", s.UserName))
        if err != nil {
            return nil, err
        }
        defer resp.Body.Close()

        // unmarshal score data
        var data struct {
            Score float64 `json:"score"`
        }
        if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
            return nil, err
        }

        // set score field on Student instance
        s.Score = data.Score

        // append StudentScore
        scores = append(scores, s)
    }

    return scores, nil
}

---

要同时执行此操作，您可以执行以下操作：

type StudentScore struct {
    UserName string  `json:"user_name"`
    Score    float64 `json:"score"`
}

func GetStudentScore() ([]StudentScore, error) {
    var wg sync.WaitGroup
    var ch = make(chan StudentScore)

    for _, row := range rowsOne {
        wg.Add(1)

        // for each row execute the retrieveStudentScore in a separate goroutine
        go func() {
            if err := retrieveStudentScore(row.UserName, ch); err != nil {
                log.Println("failed to retrieve StudentScore:", err)
            }
            wg.Done()
        }()
    }
    
    go func() {
        wg.Wait() // wait until every retrieveStudentScore is finished
        close(ch) // this will cause the range loop below to exit
    }()

    var scores []StudentScore
    for s := range ch {
        // append StudentScore received from channel
        scores = append(scores, s)
    }

    return scores, nil
}

func retrieveStudentScore(userName string, ch chan StudentScore) error {
    // request score data
    resp, err := http.Get(fmt.Sprintf("https://example.com/users/%s/score", userName))
    if err != nil {
        return err
    }
    defer resp.Body.Close()

    // unmarshal score data
    var data struct {
        Score float64 `json:"score"`
    }
    if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
        return err
    }
    
    // send StudentScore to channel
    ch <- StudentScore{UserName: userName, Score: data.Score}
    
    return nil
}