How to unmarshal JSON in to array of interface and use

问题

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
}

回答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

来源：https://stackoverflow.com/questions/50710160/how-to-unmarshal-json-in-to-array-of-interface-and-use

标签

json

interface

unmarshalling