Error unmarshalling JSON in Go that starts with an Array - json

Question

This is my code
package main
import (
"encoding/json"
"log"
)
type Data struct {
Page int
Pages int
PerPage string
Total int
CountriesList []Country
}
type Country struct {
Id string
Iso string
}
func main() {
body := []byte(`[
{
"page": 1,
"pages": 6,
"per_page": "50",
"total": 256
},
[
{
"id": "ABW",
"iso2Code": "AW"}]]`)
items := make([]Data, 10)
if err := json.Unmarshal(body, &items); err != nil {
log.Fatalf("error %v", err)
}
}
I'm try to unmarshall some JSON and getting the following error:
error json: cannot unmarshal array into Go value of type main.Data

Answer 1

When reading the question, I assumed that there could be multiple Data + list of Country pairs. Here's the solution I ended up with:
package main
import (
"encoding/json"
"fmt"
"log"
)
type Data struct {
Page int
Pages int
PerPage string `json:"per_page, string"`
Total int
}
type Country struct {
Id string
Iso2Code string
}
type DataCountry struct {
Data Data
CountryList []Country
}
func main() {
body := []byte(`[
{
"page": 1,
"pages": 6,
"per_page": "50",
"total": 256
},
[
{
"id": "ABW",
"iso2Code": "AW"}]
]`)
raw := make([]json.RawMessage, 10)
if err := json.Unmarshal(body, &raw); err != nil {
log.Fatalf("error %v", err)
}
sdc := make([]DataCountry, 0)
for i := 0; i < len(raw); i += 2 {
dc := DataCountry{}
data := Data{}
if err := json.Unmarshal(raw[i], &data); err != nil {
fmt.Println("error %v", err)
} else {
dc.Data = data
}
var countries []Country
if err := json.Unmarshal(raw[i+1], &countries); err != nil {
fmt.Println("error %v", err)
} else {
dc.CountryList = countries
}
sdc = append(sdc, dc)
}
fmt.Printf("%v\n", sdc)
}
I found the blog post "Using go to unmarshal json lists with multiple types" very useful for understanding several different options for dealing parsing JSON lists.

Answer 2

package main
import (
"encoding/json"
"fmt"
"log"
)
type Data struct {
Page int
Pages int
Per_Page string
Total int
CountriesList []Country
}
type Country struct {
Id string
Iso2Code string
}
func main() {
body := []byte(`
[
{
"page": 1,
"pages": 6,
"per_page": "50",
"total": 256,
"countrieslist": [
{
"id": "ABW",
"iso2Code": "AW"
}
]
}
]
`)
items := make([]Data, 10)
if err := json.Unmarshal(body, &items); err != nil {
log.Fatalf("error %v", err)
}
fmt.Printf("%#v\n", items)
}
Playground
Output:
[]main.Data{main.Data{Page:1, Pages:6, Per_Page:"50", Total:256, CountriesList:[]main.Country{main.Country{Id:"ABW", Iso2Code:"AW"}}}}

Answer 3

I got some help from #go-nuts on IRC:
package main
import (
"encoding/json"
"fmt"
"log"
)
type T1 struct {
Page, Pages, Total int
PerPage int `json:"per_page,string"`
}
type T2 struct {
ID string
ISO2Code string
}
func main() {
body := []byte(`
[
{
"page": 1,
"pages": 6,
"per_page": "50",
"total": 256
},
[
{
"id": "ABW",
"iso2Code": "AW"
},
{
"id": "AFG",
"iso2Code": "AF"
}
]
]
`)
t1 := T1{}
t2 := []T2{}
if err := json.Unmarshal(body, &[]interface{}{&t1, &t2}); err != nil {
log.Fatalf("error %v", err)
}
fmt.Printf("%#v %#v", t1, t2)
for k, v := range t2 {
fmt.Printf("%v %v\n",k, v.ID)
}
}