MongoDB中JavaScript代码的服务器端执行与字段值动态赋值

func mongoNow() bson.JavaScript {
    return bson.JavaScript{Code: "(new Date()).ISODate('YYYY-MM-DD hh:mm:ss')"}
}

// ... 在插入操作中
err := c.Insert(
   struct{Serial, Priority, Url, LastSeen interface{}}{ 
      Url: getInformedHost() + ":" + getRunningPortString(), 
      Priority: rand.Int(), 
      LastSeen: mongoNow() } // 此处传入的是bson.JavaScript对象
)

{
    "_id": ObjectId("502d6f984eaead30a134fa10"),
    "priority": 1694546828,
    "url": "127.0.0.1:8080",
    "lastseen": {
        "_bsontype": "Code",
        "code": "(new Date()).ISODate('YYYY-MM-DD hh:mm:ss')",
        "scope": {}
    }
}

// 执行简单的JavaScript并获取返回值
db.eval("new Date().toISOString()"); 
// 结果可能类似 "2023-10-27T10:30:00.000Z"

// 执行一个包含计算的JavaScript
db.eval("function add(a, b) { return a + b; } add(10, 20);");
// 结果为 30

package main

import (
    "fmt"
    "log"
    "time"

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

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("testdb")
    collection := db.C("documents")

    // 1. 使用eval命令获取服务器当前时间
    var serverTime interface{} // eval返回的结果类型可能为BSON Date, String等，用interface{}接收更通用
    err = db.Run(bson.M{"eval": "new Date();"}, &serverTime)
    if err != nil {
        log.Fatalf("Failed to execute eval command for server time: %v", err)
    }
    fmt.Printf("Server-side evaluated date: %v (Type: %T)\n", serverTime, serverTime)

    // 2. 将eval获取的值用于文档插入
    docToInsert := bson.M{
        "name":        "DocumentWithServerTime",
        "description": "This document includes a timestamp evaluated on the MongoDB server.",
        "creationTime": serverTime, // 将eval的结果赋值给字段
    }

    err = collection.Insert(docToInsert)
    if err != nil {
        log.Fatalf("Failed to insert document: %v", err)
    }
    fmt.Println("Document inserted successfully with server-side evaluated time.")

    // 另一个eval示例：执行一个简单的计算
    var sumResult float64
    err = db.Run(bson.M{"eval": "function calculateSum(a, b) { return a + b; } calculateSum(15, 25);"}, &sumResult)
    if err != nil {
        log.Fatalf("Failed to execute eval for sum: %v", err)
    }
    fmt.Printf("Server-side evaluated sum: %f\n", sumResult)
}

// 在MongoDB Shell中存储一个名为"getServerTime"的函数
db.system.js.save({
    _id: "getServerTime",
    value: function() {
        return new Date(); // 返回当前服务器时间
    }
});

// 存储另一个计算函数
db.system.js.save({
    _id: "multiply",
    value: function(a, b) {
        return a * b;
    }
});

// MongoDB Shell中调用
db.eval("getServerTime()");
db.eval("multiply(7, 8)"); // 结果为 56

// Go语言（mgo驱动）中调用
// 调用存储的getServerTime函数
var storedServerTime interface{}
err = db.Run(bson.M{"eval": "getServerTime();"}, &storedServerTime)
if err != nil {
    log.Fatalf("Failed to call stored function getServerTime: %v", err)
}
fmt.Printf("Result from stored function 'getServerTime': %v\n", storedServerTime)

// 调用存储的multiply函数
var productResult float64
err = db.Run(bson.M{"eval": "multiply(12, 5);"}, &productResult)
if err != nil {
    log.Fatalf("Failed to call stored function multiply: %v", err)
}
fmt.Printf("Result from stored function 'multiply': %f\n", productResult)