问题
Given a go struct
type Company struct {
ID int `json:"id"`
Abn sql.NullString `json:"abn,string"`
}
when marshalled with something like this
company := &Company{}
company.ID = 68
company.Abn = "SomeABN"
result, err := json.Marshal(company)
the result is
{
"id": "68",
"abn": {
"String": "SomeABN",
"Valid": true
}
}
The result desired is
{
"id": "68",
"abn": "SomeABN"
}
I've tried explicitly stating that Abn is a string.
Abn sql.NullString `json:"abn,string"`
which did not change the result.
How do you marshal a sql.NullString such that the output is flattened to give just the value in go?
EDIT
Something like I ended up with after reading the answers from https://stackoverflow.com/users/8256506/nilsocket and https://stackoverflow.com/users/965900/mkopriva
package main
import (
"database/sql"
"encoding/json"
"reflect"
//"github.com/lib/pq"
)
/*
https://medium.com/aubergine-solutions/how-i-handled-null-possible-values-from-database-rows-in-golang-521fb0ee267
*/
type NullString sql.NullString
func (x *NullString) MarshalJSON() ([]byte, error) {
if !x.Valid {
x.Valid = true
x.String = ""
//return []byte("null"), nil
}
return json.Marshal(x.String)
}
// Scan implements the Scanner interface for NullString
func (ns *NullString) Scan(value interface{}) error {
var s sql.NullString
if err := s.Scan(value); err != nil {
return err
}
// if nil then make Valid false
if reflect.TypeOf(value) == nil {
*ns = NullString{s.String, false}
} else {
*ns = NullString{s.String, true}
}
return nil
}
type Company struct {
ID int `json:"id"`
Abn NullString `json:"abn"`
}
回答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.
回答2:
You cannot, at least not using just sql.NullString
and encoding/json
.
What you can do is to declare a custom type that embeds sql.NullString
and have that custom type implement the json.Marshaler
interface.
type MyNullString struct {
sql.NullString
}
func (s MyNullString) MarshalJSON() ([]byte, error) {
if s.Valid {
return json.Marshal(s.String)
}
return []byte(`null`), nil
}
type Company struct {
ID int `json:"id"`
Abn MyNullString `json:"abn,string"`
}
https://play.golang.org/p/Ak_D6QgIzLb
来源:https://stackoverflow.com/questions/51961358/how-do-you-marshal-a-sql-nullstring-such-that-the-output-is-flattened-to-give-ju