Error Parsing Json using Go language

Question

I am trying to Parse Json & Print Data and save in a CSV using GO language .

It is printing the desired 10 result per page with Println but couldn't parse JSON .

This is what I am doing

Visitor visits studentresults.com/page=1 RollNo. & Marks for 10 students are displayed and it is also saved in a CSV [key.rollno & key.marks]

Program Makes a request to studentsapimarks.com/api/rollno1,rollno2,rollno3/detail (appending all key.rollno that we got in step1) The Json response would be like

[{"name":"James","Percentage":96.5,"Remarks":"VeryGood"}, {"name":"William","Percentage":36.0,"Remarks":"Bad"}, {"name":"Jacob","Percentage":63.0,"Remarks":"Average"}, {"name":"Wilson","Percentage":69.3,"Remarks":"Average"}, {"name":"Kurtson","Percentage":16.9,"Remarks":"VeryBad"}, {"name":"Tom","Percentage":86.3,"Remarks":"Good"}]

Extract Name & Percentage fields & save in a csv

Here is my snippet of the code that is responsible for printing and saving the results

package main import ( "encoding/csv" "fmt" "net/http" "os" "strings" "encoding/json" ) type Key struct { fname string marks int rollno int } type object struct { Percentage float64 Name string `json:"name"` } func PageRequest(w http.ResponseWriter, r *http.Request) { // Page header fmt.Fprintf(w, PageHeader, pages, previous, next) // Save in csv csvfile, err := os.OpenFile("marks.csv", os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666) if err != nil { fmt.Println("Error:", err) return } defer csvfile.Close() writer := csv.NewWriter(csvfile) defer writer.Flush() // Defining RollNos var rollNos []string // Marks for UID UID, length := compute(start) for i := 0; i < length; i++ { key := UID[i] // Prints firstname, Marks and Rollno fmt.Fprintf(w, key.fname, key.marks, key.rollno) records := [][]string{{key.fname, key.marks, key.rollno}} for _, record := range records { err := writer.Write(record) if err != nil { fmt.Println("Error:", err) return } } // Append All key.rollno rollNos := append(rollNos, key.rollno) // Makes a request to as studentsapimarks.com/api/rollno1,rollno2,rollno3/detail uri := "https://studentsapimarks.com/api/" + strings.Join(rollNos, ",") + "/detail" res, err := http.Get(uri) if err != nil { log.Fatal(err) } defer res.Body.Close() var s []object err = json.NewDecoder(res.Body).Decode(&s) if err != nil { log.Fatal(err) } // Prints Name/ Percentage fmt.Println(s[0].Name) fmt.Println(s[0].Percentage) } // Page Footer fmt.Fprintf(w, PageFooter, previous, next) } func main() { http.HandleFunc("/", PageRequest) log.Println("Listening") log.Fatal(http.ListenAndServe(":8080", nil)) }

fmt.Fprintf(w, key.fname, key.marks, key.rollno) is working fine and displays all 10 results per page and saves in a csv .

Problem with the code is

It is not appending all key.rollno that we got in step1 as studentsapimarks.com/api/rollno1,rollno2,rollno3/detail
Also how could i save the JSON extracted s[0].name results in a CSV ?

Adrian · Accepted Answer · 2017-07-07 15:38:37Z

The JSON parsing is failing because you're trying to unmarshal a JSON array into a struct. You want to unmarshal a JSON array into a slice - the outer struct is not necessary:

var s []object err = json.NewDecoder(res.Body).Decode(&s)

Also, it can only unmarshal exported fields (those that start with a capital letter), so to get the name, you'll need to change your struct definition. I'm guessing the percentage isn't coming through either, since in the JSON it's a single float value, but in your struct you're taking a float slice.

type object struct { // "Percentage": 96.4 is not a slice. // Also if the field name in Go and JSON are identical, you dont need the json tag. Percentage float64 // The field must be capitalized, the tag can stay lowercase Name string `json:"name"` }

Then you'll access those fields accordingly:

// Prints Name/ Percentage fmt.Println(s[0].Name) fmt.Println(s[0].Percentage)

removed type object struct & type ObjectsAPIResponse struct and used var s []object now getting error undefined: object
That's because you removed the object type. I gave you an updated definition for it - don't remove it, use the updated definition.
now error s.Allmarks undefined (type []object has no field or method Allmarks)
removed type ObjectsAPIResponse struct and used var s []object and modified fmt.Println(s.Allmarks[0].name) to fmt.Println(s.[0].name)

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