使用golang mongodb统计流水线中的分组记录总数

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

func connectDB() (*mongo.Client, error) {
    clientOptions := options.Client().ApplyURI("mongodb://localhost:27017")
    client, err := mongo.Connect(context.TODO(), clientOptions)
    if err != nil {
        return nil, err
    }
    err = client.Ping(context.TODO(), nil)
    if err != nil {
        return nil, err
    }
    fmt.Println("Connected to MongoDB!")
    return client, nil
}

func countGroupedRecords() (int64, error) {
    client, err := connectDB()
    if err != nil {
        return 0, err
    }
    collection := client.Database("your_database").Collection("your_collection")
    
    pipeline := []bson.M{
        bson.M{"$group": bson.M{"_id": "$field_to_group_by", "count": bson.M{"$sum": 1}}},
        bson.M{"$group": bson.M{"_id": nil, "total_count": bson.M{"$sum": "$count"}}},
    }
    
    cursor, err := collection.Aggregate(context.TODO(), pipeline)
    if err != nil {
        return 0, err
    }
    
    defer cursor.Close(context.TODO())
    
    var result struct {
        TotalCount int64 `bson:"total_count"`
    }
    
    if cursor.Next(context.TODO()) {
        err = cursor.Decode(&result)
        if err != nil {
            return 0, err
        }
    }
    
    return result.TotalCount, nil
}

func main() {
    totalCount, err := countGroupedRecords()
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    fmt.Println("Total Count:", totalCount)
}