How to unmarshal JSON in to array of interface and use - json

Question

I am having difficulty understanding how to correctly unmarshal some JSON data that goes in to an array of type inteface and then use it. I tried to make this example code as simple as possible to illustrate the problem I am having. The code can be found in the playground here: https://play.golang.org/p/U85J_lBJ7Zr
The output looks like:
[map[ObjectType:chair ID:1234 Brand:Blue Inc.] map[ID:5678
Location:Kitchen ObjectType:table]] { } false { } false
Code
package main
import (
"fmt"
"encoding/json"
)
type Chair struct {
ObjectType string
ID string
Brand string
}
type Table struct {
ObjectType string
ID string
Location string
}
type House struct {
Name string
Objects []interface{}
}
func main() {
var h House
data := returnJSONBlob()
err := json.Unmarshal(data, &h)
if err != nil {
fmt.Println(err)
}
fmt.Println(h.Objects)
s1, ok := h.Objects[0].(Table)
fmt.Println(s1, ok)
s2, ok := h.Objects[0].(Chair)
fmt.Println(s2, ok)
}
func returnJSONBlob() []byte {
s := []byte(`
{
"Name": "house1",
"Objects": [
{
"ObjectType": "chair",
"ID": "1234",
"Brand": "Blue Inc."
},
{
"ObjectType": "table",
"ID": "5678",
"Location": "Kitchen"
}
]
}
`)
return s
}

Answer 1

I'm not sure if this is practical, since this is a simplified version of your scenario. However, one way to do this is combine the two object types to a new one, Object, and then unmarshal them directly to Object instead of using interface{}:
package main
import (
"encoding/json"
"fmt"
)
type Object struct {
ObjectType string
ID string
Brand string
Location string
}
type House struct {
Name string
Objects []Object
}
func returnJSONBlob() []byte {
s := []byte(`
{
"Name": "house1",
"Objects": [
{
"ObjectType": "chair",
"ID": "1234",
"Brand": "Blue Inc."
},
{
"ObjectType": "table",
"ID": "5678",
"Location": "Kitchen"
}
]
}
`)
return s
}
func main() {
var h House
data := returnJSONBlob()
err := json.Unmarshal(data, &h)
if err != nil {
fmt.Println(err)
}
fmt.Println(h.Objects[0].Brand)
fmt.Println(h.Objects[1].Location)
}
Prints:
Blue Inc.
Kitchen
Example here: https://play.golang.org/p/91F4UrQlSjJ