golang 监听mongodb的集合，只监听指定字段例如 name 字段，提取该指定字段，并在 pipeline 中设置$project-Go服务器开发

要在Golang中监听MongoDB集合并提取指定字段，您可以使用MongoDB的Change Streams功能结合Go的mgo.v2库。下面是一个简单的示例代码：

package main
import (
	"context"
	"fmt"
	"log"
	"time"
	"gopkg.in/mgo.v2"
)
func main() {
	session, err := mgo.Dial("mongodb://localhost:27017")
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()
	collection := session.DB("your_database").C("your_collection")
	pipeline := []bson.M{
		bson.M{"$match": bson.M{}},
		bson.M{"$project": bson.M{"name": 1}},
	}
	options := mgo.ChangeStreamOptions{
		Pipeline:      pipeline,
		BatchSize:     1,
        FullDocument:  "updateLookup",
        MaxAwaitTimeMS: time.Duration(500),
	}
	stream := collection.Watch(context.Background(), mongo.Pipeline{}, options)
	defer stream.Close()
	for {
	    // 从change stream读取变更事件
	    if stream.Next(context.Background()) {
	        changeEvent := &bson.Raw{}
	        if err := stream.Decode(changeEvent); err != nil {
	            log.Println("Failed to decode change event:", err)
	            continue
	        }
	        // 提取所需字段，这里假设'name'字段是字符串类型
            nameValue, ok := changeEvent.Lookup("fullDocument.name").StringValue()
            if ok {
                fmt.Println("Name:", nameValue)
            }
	    } else if err := stream.Err(); err != nil {
	        log.Println("Error occurred while listening for changes:", err)
	        break
	    }
	    
	    time.Sleep(time.Millisecond * 100) // 避免过于频繁的循环
	}
}