在golang中获取json上的可空对象解组

Question

Go code(jsonTestParse.go)

(this is just a test example I made, please don't argue that I should use list of students in cls struct)

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "os"
)

type student struct {
    ID       string `json:"id"`
    Name     string `json:"name"`
    Standard string `json:"std"`
}

type cls struct {
    st student `json:"cls"`
}

func getValues() (cls, error) {
    var clss cls
    dataBytes, err := ioutil.ReadFile("studentclass.json")
    if err != nil {
        fmt.Printf("File error: %v
", err)
        os.Exit(1)
    }
    err = json.Unmarshal(dataBytes, &clss)
    if err != nil {
        fmt.Errorf("%s", err)
    }
    return clss, err
}

func main() {
    s, err := getValues()
    fmt.Printf("%#v
", s)
    fmt.Println(err)
}

Json File (studentclass.json)

{
    "cls": {
        "id": "1",
        "name": "test",
        "std": "0"
    }
}

When I run this code with go run jsonTestParse.go it gives me this output:

main.cls{st:main.student{ID:"", Name:"", Standard:""}}
<nil>

Please help me why I'm getting this blank object

main.cls{st:main.student{ID:"", Name:"", Standard:""}}

instead of this

main.cls{st:main.student{ID:"1", Name:"test", Standard:"0"}}

Plus It would be great to help on how to get these values?

Answer 1

That is because your cls struct has embedded private struct (lower case unexported field) of student st, change to exported field should work, that is:

type cls struct {
    // St field will be unmarshalled
    St student `json:"cls"`
}

See in playground