golang mongodb中的过滤器

import (
    "context"
    "fmt"
    "go.mongodb.org/mongo-driver/bson"
    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"
)

func main() {
    clientOptions := options.Client().ApplyURI("mongodb://localhost:27017")
    client, err := mongo.Connect(context.Background(), clientOptions)
    if err != nil {
        fmt.Println("Failed to connect to MongoDB:", err)
        return
    }

    collection := client.Database("testdb").Collection("testcollection")

    filter := bson.D{{"name", "John"}, {"age", bson.D{{"$gte", 30}}}}

    cur, err := collection.Find(context.Background(), filter)
    if err != nil {
        fmt.Println("Failed to find documents:", err)
        return
    }

    for cur.Next(context.Background()) {
        var result bson.M
        err := cur.Decode(&result)
        if err != nil {
            fmt.Println("Failed to decode document:", err)
            return
        }

        fmt.Println(result)
    }

    if err := cur.Err(); err != nil {
        fmt.Println("Cursor error:", err)
        return
    }

    cur.Close(context.Background())
}