Is there a simple way to decode different objects in an array of json by golang?

Question

A json stream described an array of shapes. The shapes mayb be triangles, rectangles or squares.

For example:

{"shapes": [
    {"type": "triangle", "side1": 3, "side2": 4, "side3": 5},
    {"type": "rectangle", "width": 4, "height": 3},
    {"type": "square", "side": 3}
]}

These structures are declared in my golang code:

type Shape struct {
    Type string `json:"type"`
}

type Triangle struct {
    Shape
    Side1 int `json:"side1"`
    Side2 int `json:"side2"`
    Side3 int `json:"side3"`
}

type Rectangle struct {
    Shape
    Width  int `json:"width"`
    Height int `json:"height"`
}

type Square struct {
    Shape
    Side int `json:"side"`
}

How can I decode the json into an object slice? Thank you very much.

nipuna · Accepted Answer · 2021-06-12 05:41:09Z

Create new type Shapesto unmarshal shapes and implement your custom UnmarshalJSON to Shapes

type Shapes struct {
    Shapes []interface{} `json:"shapes"`
}

func (b *Shapes) UnmarshalJSON(data []byte) error {

    var v = struct {
        Shapes []map[string]interface{} `json:"shapes"`
    }{}
    if err := json.Unmarshal(data, &v); err != nil {
        return err
    }
    types := make([]interface{}, 0)

    for _, shape := range v.Shapes {
        shp := Shape{Type: shape[`type`].(string)}
        switch shp.Typ() {
        case `triangle`:
            typ := Triangle{
                Shape:shp,
                Side1: int(shape[`side1`].(float64)),
                Side2: int(shape[`side2`].(float64)),
                Side3: int(shape[`side3`].(float64)),
            }
            types = append(types, typ)
        case `rectangle`:
            typ := Rectangle{
                Shape:  shp,
                Width:  int(shape[`width`].(float64)),
                Height: int(shape[`height`].(float64)),
            }
            types = append(types, typ)
        case `square`:
            typ := Square{
                Shape:  shp,
                Side:  int(shape[`side`].(float64)),
            }
            types = append(types, typ)
        }
    }

    b.Shapes = types

    return nil
}

Unmarshal json string to Shapes type. You can access your shape types in Shapes.Shapes array.

func main() {
    jStr := `{"shapes": [
    {"type": "triangle", "side1": 3, "side2": 4, "side3": 5},
    {"type": "rectangle", "width": 4, "height": 3},
    {"type": "square", "side": 3}
]}`

    shapes := Shapes{}
    err := json.Unmarshal([]byte(jStr), &shapes)
    if err != nil {
        panic(err)
    }
    fmt.Println(shapes)
}

Find full code here

Collectives™ on Stack Overflow

Is there a simple way to decode different objects in an array of json by golang?

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related