将自定义类型转换为类型 [][]float64

Posted 2023-03-29

【中文标题】将自定义类型转换为类型 [][]float64

【英文标题】：Convert custom type to type [][]float64

【发布时间】：2022-01-22 01:35:43

【问题描述】：

使用 Golang，我想从数据库中获取这些跟踪点（纬度、经度）以生成如下所示的 GeoJSON 文件：

"type":"FeatureCollection","features":["type":"Feature","geometry":"type":"LineString","coordinates":[[-122.271154,37.804348],[-122.272057,37.80295],[-122.272057,37.80295],[-122.278011,37.805288]],"properties":null]

这是我的代码：

package main

import (
    "fmt"
    "log"
    "net/http"
    "time"

    "github.com/gorilla/mux"
    "github.com/jinzhu/gorm"
    _ "github.com/jinzhu/gorm/dialects/mysql"
    geojson "github.com/paulmach/go.geojson"
    "github.com/shopspring/decimal"
)

var db *gorm.DB
var err error

type Trackpoint struct 
    Id        int             `json:"-"`
    Latitude  decimal.Decimal `json:"lat" sql:"type:decimal(10,8);"`
    Longitude decimal.Decimal `json:"long" sql:"type:decimal(11,8);"`
    Elevation uint
    Timestamp time.Time


func returnTrackpoints(w http.ResponseWriter, r *http.Request) 
    trackpoints := []Trackpoint
    db.Find(&trackpoints)
    coordinates := [][]float64-122.271154, 37.804348, -122.272057, 37.80295, -122.272057, 37.80295, -122.278011, 37.805288
    fc := geojson.NewFeatureCollection()
    fmt.Println(coordinates)
    fc.AddFeature(geojson.NewLineStringFeature(coordinates))
    rawJSON, err := fc.MarshalJSON()
    if err != nil 
        fmt.Println(err)
    
    fmt.Fprintf(w, "%s", string(rawJSON))


func handleRequests() 
    log.Println("Starting development server at http://127.0.0.1:10000/")
    myRouter := mux.NewRouter().StrictSlash(true)
    myRouter.HandleFunc("/trackpoints", returnTrackpoints)
    log.Fatal(http.ListenAndServe(":10000", myRouter))


func main() 
    db, err = gorm.Open("mysql", "user:password&@tcp(127.0.0.1:3306)/database?charset=utf8&parseTime=True")

    if err != nil 
        log.Println("Connection Failed to Open")
     else 
        log.Println("Connection Established")
    

    db.AutoMigrate(&Trackpoint)
    handleRequests()

如果我使用

fc.AddFeature(geojson.NewLineStringFeature(coordinates)) GeoJSON 输出看起来不错。

但我想使用数据库中的坐标，例如

fc.AddFeature(geojson.NewLineStringFeature(trackpoints))

使用我存储在数据库中的 GPS 数据，但出现错误

./main.go:33:44: cannot use trackpoint (type []Trackpoint) as type [][]float64 in argument to geojson.NewLineStringFeature

如何将 []Trackpoint 类型转换为 [][]float64？

【参考方案1】：

使用与跟踪点相同数量的元素制作切片 循环遍历每个跟踪点 Convert decimal.Decimal types to float64 在切片中设置 float64 坐标 将新切片传递给fc.AddFeature

func returnTrackpoints(w http.ResponseWriter, r *http.Request) 
    trackpoints := []Trackpoint
    db.Find(&trackpoints)
    
    coordinates := make([][]float64, len(trackpoints))
    for i, trackpoint := range trackpoints 
        lat, _ := trackpoint.Latitude.Float64()
        long, _ := trackpoint.Longitude.Float64()
        coordinates[i] = []float64
            lat,
            long,
        
    
    fc := geojson.NewFeatureCollection()
    fmt.Println(coordinates)
    fc.AddFeature(geojson.NewLineStringFeature(coordinates))
    rawJSON, err := fc.MarshalJSON()
    if err != nil 
        fmt.Println(err)
    
    fmt.Fprintf(w, "%s", string(rawJSON))