为选择查询传递可变参数答案

【问题标题】：Passing a variadic parameter for select query为选择查询传递可变参数
【发布时间】：2016-04-05 19:08:15
【问题描述】：

我正在尝试如下构建查询，这里我使用的是 gorp。

func GetAgregatedDownloadsFromTo(constrains Constrains) [] dao.NameValue {
    dbMap := utils.GetDBConnection("radsummary");
    defer dbMap.Db.Close()
    var totalDailyDownloads[] NameValue
    query := "SELECT SUM(outputoctets) as value ,date as name FROM dailyacct where date >= ? AND date < ? "

    if len(constrains.LocationGroups) > 0 {
        query = query + " AND calledstationid=? "
        for i := 1; i< len(constrains.LocationGroups); i++ {
            query = query + " OR calledstationid=? "
        }
        query = query + " group by date"
        print(query)
        _, err := dbMap.Select(&totalDailyDownloads, query, constrains.From, constrains.To, constrains.LocationGroups...)
        if err != nil {
            panic(err.Error()) // proper error handling instead of panic
        }
    }
    return totalDailyDownloads
}

type Constrains struct {
    From string `json:"from"`
    To string   `json:"to"`
    LocationGroups []string    `json:"locationgroups"`
}

查询构造基于约束.LocationGroups 的长度。我遇到的麻烦是将可变数量的 args 传递给 Select 查询，一旦我给出了 constrains.LocationGroups... 作为选择查询参数，它会引发编译器错误too many arguments in call to dbMap.Select

是否有可能实现这种要求？感谢您的意见。

【问题讨论】：

标签： mysql go gorp

【解决方案1】：

根据Pass string slice to variadic empty interface parameter找到答案

下面是实现任务的更新代码

func GetAgregatedDownloadsFromTo(constrains dao.Constrains) [] dao.NameValue {
    dbMap := utils.GetDBConnection("radsummary");
    defer dbMap.Db.Close()
    var totalDailyDownloads[] dao.NameValue
    query := "SELECT SUM(outputoctets) as value ,date as name FROM dailyacct where date >= ? AND date < ? "

    if len(constrains.LocationGroups) > 0 {
        args := make([]interface{}, len(constrains.LocationGroups)+2)
        args[0] = constrains.From
        args[1] = constrains.To
        for index, value := range constrains.LocationGroups { args[index+2] = value }

        query = query + " AND calledstationid=? "
        for i := 1; i< len(constrains.LocationGroups); i++ {
            query = query + " OR calledstationid=? "
        }
        query = query + " group by date"
        print(query)
        _, err := dbMap.Select(&totalDailyDownloads, query, args...)
        if err != nil {
            panic(err.Error()) // proper error handling instead of panic
        }
    }
    return totalDailyDownloads
}

这里我必须将字符串切片转换为接口切片。

【讨论】：