CODEWITHSUNDEEP
jsongo
magiconair
magiconair

Reputation: 6997

Converting Go struct to JSON

I am trying to convert a Go struct to JSON using the json package but all I get is {}. I am certain it is something totally obvious but I don't see it.

package main

import (
    "fmt"
    "encoding/json"
)

type User struct {
    name string
}

func main() {
    user := &User{name:"Frank"}
    b, err := json.Marshal(user)
    if err != nil {
        fmt.Printf("Error: %s", err)
        return;
    }
    fmt.Println(string(b))
}

Then when I try to run it I get this:

$ 6g test.go && 6l -o test test.6 && ./test 
{}

Upvotes: 336

Views: 543984

Answers (2)

Hieu Vo
Hieu Vo

Reputation: 3274

You can define your own custom MarshalJSON and UnmarshalJSON methods and intentionally control what should be included, ex:

package main

import (
    "fmt"
    "encoding/json"
)

type User struct {
    name string
}

func (u *User) MarshalJSON() ([]byte, error) {
    return json.Marshal(&struct {
        Name     string `json:"name"`
    }{
        Name:    u.name,
    })
}

func main() {
    user := &User{name: "Frank"}
    b, err := json.Marshal(user)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println(string(b))
}

Upvotes: 13

peterSO
peterSO

Reputation: 166529

You need to export the User.name field so that the json package can see it. Rename the name field to Name.

package main

import (
    "fmt"
    "encoding/json"
)

type User struct {
    Name string
}

func main() {
    user := &User{Name: "Frank"}
    b, err := json.Marshal(user)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println(string(b))
}

Output:

{"Name":"Frank"}

Upvotes: 561

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