mongodb - 如何使用findone从Mongodb集合返回数组

Question

我正在使用查找一个来找到特定的user_id并返回特定文档中的data数组。

下面是我的文档结构

package main

import (
    "context" // manage multiple requests
    "fmt"     // Println() function
    "os"
    "reflect" // get an object type

    // import 'mongo-driver' package libraries
    "go.mongodb.org/mongo-driver/bson"
    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"
)

type Fields struct {
    user_id string
    data  struct {
        year string
        day string
        revenue int
    }
    max int
}

func main() {
    // Declare host and port options to pass to the Connect() method
    clientOptions := options.Client().ApplyURI("mongodb://localhost:27017")

    // Connect to the MongoDB and return Client instance
    client, err := mongo.Connect(context.TODO(), clientOptions)
    if err != nil {
        fmt.Println("mongo.Connect() ERROR:", err)
        os.Exit(1)
    }

    // Declare Context type object for managing multiple API requests
    // Access a MongoDB collection through a database
    col := client.Database("graph").Collection("alltime")
    fmt.Println("Collection type:", reflect.TypeOf(col), "\n")

    // Declare an empty array to store documents returned
    var result Fields

    // Get a MongoDB document using the FindOne() method
    err = col.FindOne(context.TODO(), bson.D{{"user_id", "11664"}}).Decode(&result)
    if err != nil {
        fmt.Println("FindOne() ERROR:", err)
        os.Exit(1)
    } else {
        // fmt.Println("FindOne() result:", result)
        fmt.Println("FindOne() Name:", result.data)
        // fmt.Println("FindOne() Dept:", result.Dept)
    }


}

但这是我得到的输出

varun@Varuns-MacBook-Air sql-test % go run mongofind.go
Collection type: *mongo.Collection 

FindOne() Name: {  0}

Answer 1

驱动程序需要使用反射来设置字段，并且要使反射起作用，必须导出结构字段。导出它们时，名称不再与数据库名称匹配，因此必须添加bson标记。另外，您的Data字段不是struct中的数组:

type Fields struct {
    User_id string `bson:"user_id"`
    Data  []struct {
        Year string `bson:"year"`
        Day string `bson:"day"`
        Revenue int `bson:"revenue"`
    } `bson:"data"`
    Max int `bson:"max"`
}