如何将字符串类型的 url 参数转换为我的 mongodb 查询可接受的类型？

Question

我正在尝试通过从 get 请求发送的 url 参数从我的 mongodb 中查找和检索相关数量的字段。

func main() {
    r := mux.NewRouter()
    r.HandleFunc("/user", createUser).Methods("POST")
    r.HandleFunc("/suggest", searchCity).Methods("GET") // The route for the function

    fmt.Println("Server running at port 8080")
    log.Fatal(http.ListenAndServe(":8080", r))

}

func searchCity(w http.ResponseWriter, r *http.Request) {
    //ctx := context.Background()
    DB := setup() // setup() returns a mongo.Database type
    values := r.URL.Query()
    city := values.Get("city_name") // so the route would ultimately be `/suggest?city_name=<cityname>` (I think?)

    cityCollection := DB.Collection("city")

    cursor, err := cityCollection.Find(r.Context(), city) // options.Find().SetProjection(projection))
    if err != nil {
        log.Fatal(err)
    }

    var cityList []bson.M
    if err = cursor.All(r.Context(), &cityList); err != nil {
        log.Fatal(err)
    }
    for _, cityList := range cityList {
        fmt.Println(cityList["all_names"])
        fmt.Println(cityList["country_name"])
    }
}

我特别想从集合中返回all_names 和country_name 字段并尝试使用SetProjection()，但我可能使用不正确，因此不确定。

但是，我不断收到此错误：

cannot transform type string to a BSON Document: WriteString can only write while positioned on a Element or Value but is positioned on a TopLevel

有没有办法将其转换为 mongodb 驱动程序可以接受的格式？

Answer 1

如documented错误提示，需要通过bson包使用bson对象查询mongodb。

collection.Find(ctx, bson.D{{"name", city}})

以下是一个工作示例，我根据您的评论对其进行了测试。

package main

import (
    "context"
    "encoding/json"
    "log"
    "net/http"
    "time"

    "go.mongodb.org/mongo-driver/bson"
    "go.mongodb.org/mongo-driver/bson/primitive"
    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"
)

func cityHandler(collection *mongo.Collection) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        ctx := r.Context()
        city := r.URL.Query().Get("city_name")
        var q bson.D
        if city != "" {
            q = bson.D{{"name", city}}
        } else {
            q = bson.D{{}}
        }

        cur, currErr := collection.Find(ctx, q)
        if currErr != nil {
            http.Error(w, currErr.Error(), http.StatusInternalServerError)
        }
        defer cur.Close(ctx)

        var result []primitive.M
        if err := cur.All(ctx, &result); err != nil {
            http.Error(w, err.Error(), http.StatusInternalServerError)
        }

        w.Header().Set("Content-Type", "application/json")
        err := json.NewEncoder(w).Encode(result)
        if err != nil {
            http.Error(w, err.Error(), http.StatusInternalServerError)
        }

    }
}

func main() {
    client, err := mongo.NewClient(options.Client().ApplyURI("mongodb://root:example@localhost:27017"))
    if err != nil {
        panic(err)
    }
    ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
    defer cancel()

    err = client.Connect(ctx)
    if err != nil {
        panic(err)
    }
    defer client.Disconnect(ctx)

    docs := []interface{}{
        bson.D{{"name", "Wuhu"}},
        bson.D{{"name", "Shexian"}},
    }

    collection := client.Database("china").Collection("cities")

    _, err = collection.InsertMany(ctx, docs)
    if err != nil {
        panic(err)
    }

    http.HandleFunc("/", cityHandler(collection))
    log.Fatal(http.ListenAndServe(":8080", nil))

}