How to convert a JSON file to CSV file with Golang

Many times I wanted to store the data from an API and look at it in another moment and don’t call the API every time.

I spent almost a whole week trying to build this program. This is a program to practice Golang and its standard library. I learn a lot in the process, I hope you do too.

This is the data we will convert:

{ "genus": "Malus", 
"name": "Apple", 
"id": 6, 
"family": "Rosaceae", 
"order": "Rosales", 
"nutrition": 
{ "carbohydrates": 11.4, 
   "protein": 0.3, 
   "fat": 0.4,
   "calories": 52, 
   "sugar": 10.3 } 
}

This is the code:

package main
import (
  "fmt"
  "io/ioutil"
  "log"
  "net/http"
  "os"
  "encoding/csv"
  "encoding/json"
)

func main() {
 // This line use the HTTP package to call the API
// and store the data in a variable.
response,err := http.Get("https://www.fruityvice.com/api/fruit/apple" )
  if err != nil {
    fmt.Print(err.Error())
    os.Exit(1)
  }
// This code reads the data stores it in the variable.
  responseData, err := ioutil.ReadAll(response.Body) 
  if err != nil {
    log.Fatal(err)
  }
// This code create a Map
//because the json file has different types of values we use "interface{}".
  var fruitObject map[string]interface{}
  err = json.Unmarshal([]byte(responseData), &fruitObject) 
  if err != nil {
    fmt.Println(err)
  }
// This code use "os" package to create the csv file inside the same directory.
  csvFile, err := os.Create("./fruits.csv") 
  if err != nil {
    fmt.Println(err)
  }
  defer csvFile.Close() // This code close the file.

//This code use enconding/csv package to write the csv file.
  writer := csv.NewWriter(csvFile) 
//This code loop through the interface and store the data 
//in a slice. The "enconding/csv" package only writes in []string.
  for k,v := range fruitObject {
    var row []string
    var b string
//This code use switch to check if the values are strings
// if is not, it will convert it to a string using string formatting(fmt.Sprintf).
    switch elemTyped := v.(type) {
    case int:
      a := fmt.Sprintf("%0.1f", elemTyped)
      row = append(row, a)
    case float64:
      a := fmt.Sprintf("%0.1f", elemTyped)
      row = append(row, a)
    case string:
      b = elemTyped
      row = append(row, b)
    case interface {}:
      c := fmt.Sprintf("%v", elemTyped)
      row = append(row, c)
    }
    //This code write the data of variable row into a csv file.
    writer.Write(row) 
  }
 //This code ensure all buffered data is written 
//in the file before closing the file.
  writer.Flush() 
  fmt.Println("csv file created")
}

Follow me on Twitter.