MongoDB服务器端JavaScript执行：动态字段值与eval命令实践

// 原始尝试：将JavaScript代码作为字段值插入
func mongoNow() bson.JavaScript {
    return bson.JavaScript{Code: 
         "(new Date()).ISODate('YYYY-MM-DD hh:mm:ss')"}
}

// ... 在插入操作中
// LastSeen: mongoNow()

package main

import (
    "fmt"
    "log"
    "math/rand"
    "time"

    "gopkg.in/mgo.v2"
    "gopkg.in/mgo.v2/bson"
)

// 假设 getInformedHost() 和 getRunningPortString() 是获取主机和端口的函数
func getInformedHost() string { return "127.0.0.1" }
func getRunningPortString() string { return "8080" }

func main() {
    session, err := mgo.Dial("mongodb://localhost:27017")
    if err != nil {
        log.Fatalf("Failed to connect to MongoDB: %v", err)
    }
    defer session.Close()

    db := session.DB("myapp")
    c := db.C("instances")

    rand.Seed(time.Now().UnixNano())

    // 1. 使用eval命令在服务器端获取当前时间
    var evalResult struct {
        ReturnValue interface{} `bson:"retval"` // eval命令的执行结果在retval字段中
        OK          int         `bson:"ok"`
    }

    // 执行JavaScript代码：(new Date()).toISOString() 获取ISO格式的日期字符串
    err = db.Run(bson.M{"eval": "(new Date()).toISOString();"}).One(&evalResult)
    if err != nil {
        log.Fatalf("Failed to evaluate JavaScript on MongoDB server: %v", err)
    }

    if evalResult.OK != 1 {
        log.Fatalf("Eval command failed: %v", evalResult)
    }

    // 2. 将eval获取到的值用于插入操作
    lastSeenValue := evalResult.ReturnValue

    document := struct {
        Serial   string      `bson:"serial"`
        Priority int         `bson:"priority"`
        Url      string      `bson:"url"`
        LastSeen interface{} `bson:"lastseen"`
    }{
        Serial:   bson.NewObjectId().Hex(), // 示例序列号
        Url:      getInformedHost() + ":" + getRunningPortString(),
        Priority: rand.Int(),
        LastSeen: lastSeenValue, // 使用eval得到的值
    }

    err = c.Insert(document)
    if err != nil {
        log.Fatalf("Could not register on MongoDB server: %v", err)
    }

    fmt.Printf("Document inserted successfully with LastSeen: %v\n", lastSeenValue)

    // 验证插入结果
    var insertedDoc struct {
        LastSeen interface{} `bson:"lastseen"`
    }
    err = c.Find(bson.M{"serial": document.Serial}).One(&insertedDoc)
    if err != nil {
        log.Fatalf("Failed to find inserted document: %v", err)
    }
    fmt.Printf("Retrieved document's LastSeen: %v (Type: %T)\n", insertedDoc.LastSeen, insertedDoc.LastSeen)
}

// 在MongoDB shell中执行
db.system.js.save(
   {
     _id: "myStoredFunction",
     value: function() {
       return (new Date()).toISOString();
     }
   }
);

// Go语言中调用存储的函数
var evalResult struct {
    ReturnValue interface{} `bson:"retval"`
    OK          int         `bson:"ok"`
}
err = db.Run(bson.M{"eval": "myStoredFunction();"}).One(&evalResult)
if err != nil {
    log.Fatalf("Failed to call stored function: %v", err)
}
// evalResult.ReturnValue 将包含 myStoredFunction 的返回值