How do you marshal a sql.NullString such that the output is flattened to give just the value in go?

Question

Given a go struct

type Company struct {
    ID   int             `json:\"id\"`              
    Abn  sql.NullString  `json:\"abn,string\"`
}

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Answer 1

Here is the code,

package main

import (
    "database/sql"
    "encoding/json"
    "fmt"
    "log"
)

//Company details
type Company struct {
    ID  int        `json:"id"`
    Abn NullString `json:"abn"`
}

//NullString is a wrapper around sql.NullString
type NullString sql.NullString

//MarshalJSON method is called by json.Marshal,
//whenever it is of type NullString
func (x *NullString) MarshalJSON() ([]byte, error) {
    if !x.Valid {
        return []byte("null"), nil
    }
    return json.Marshal(x.String)
}

func main() {
    company := &Company{}
    company.ID = 68
    //create new NullString value
    nStr := sql.NullString{String: "hello", Valid: true}
    //cast it
    company.Abn = NullString(nStr)
    result, err := json.Marshal(company)
    if err != nil {
        log.Println(err)
    }
    fmt.Println(string(result))
}

Here is the blog post which explains it in detail.