CODEWITHSUNDEEP
arraysjsonparsingdictionarygo
Maxim Samburskiy
Maxim Samburskiy

Reputation: 2001

Decode both map and array json

External API returns empty array if no items:

{"items":[]}

...or map with items:

{"items":{"1": {...}, "2": {...}}}

How can I decode both of them? I tried using this struct:

var response struct {
    Items map[string]Item
    Array []Item `json:"items"`
}

But it doesn't work.

UPDATE: Best if both (array and object) will produce a map[string]Item (empty and filled)

Upvotes: 1

Views: 1356

Answers (2)

user6169399
user6169399

Reputation:

Try this working code (A):

package main

import (
    "encoding/json"
    "fmt"
)

type Item int

type response struct {
    Items map[string]Item `json:"Items"`
    Array []Item          `json:"Array"`
}

func main() {
    var d response
    err := json.Unmarshal([]byte(`{"Items":{"A":1,"B":2,"C":3},"Array":[]}`), &d)
    if err != nil {
        panic(err)
    }
    fmt.Println(d)
}

output:

{map[C:3 A:1 B:2] []}

Try this working code (B):

package main

import (
    "encoding/json"
    "fmt"
)

type Item int

type response struct {
    Items map[string]Item `json:"Items"`
    //Array []Item          `json:"Array"`
}

func main() {
    var d response
    err := json.Unmarshal([]byte(`{"Items":{"A":1,"B":2,"C":3},"Array":[]}`), &d)
    if err != nil {
        panic(err)
    }
    fmt.Println(d)
}

output:

{map[C:3 A:1 B:2]}

You may use json.Marshal and json.Unmarshal, like this working code (C):

package main

import (
    "encoding/json"
    "fmt"
)

type Item int

type response struct {
    Items map[string]Item `json:"Items"`
    Array []Item          `json:"Array"`
}

func main() {
    var test = response{
        Items: map[string]Item{"A": 1, "B": 2, "C": 3},
        Array: []Item{},
    }
    body, err := json.Marshal(test)
    if err != nil {
        panic(err)
    }
    fmt.Println(string(body)) // {"Items":{"A":1,"B":2,"C":3},"Array":[]}

    var d response
    err = json.Unmarshal(body, &d)
    if err != nil {
        panic(err)
    }
    fmt.Println(d)
}

output:

{"Items":{"A":1,"B":2,"C":3},"Array":[]}
{map[A:1 B:2 C:3] []}

You may Unmarshal {"A":1,"B":2,"C":3} to map[A:1 B:2 C:3]
and "[1,2,3]" to [1 2 3], like this working code (D):

package main

import (
    "encoding/json"
    "fmt"
)

type Item int

type response1 map[string]Item
type response2 []Item

func main() {
    var d response1
    err := json.Unmarshal([]byte(`{"A":1,"B":2,"C":3}`), &d)
    if err != nil {
        panic(err)
    }
    fmt.Println(d) // map[A:1 B:2 C:3]

    var d2 response2
    err2 := json.Unmarshal([]byte(`[1,2,3]`), &d2)
    if err2 != nil {
        panic(err2)
    }
    fmt.Println(d2) // [1 2 3]
}

output: 

map[A:1 B:2 C:3]
[1 2 3]

Upvotes: 0

Kaedys
Kaedys

Reputation: 10158

If you need to unmarshall to a variable type, the easiest way is to unmarshal into a map[string]interface{} and type-assert (or in this case, type-switch) your way out.

func Unmarshal(data []byte) (map[string]Item, error) {
    var d struct {
        Items interface{} `json:"items"`
    }
    if err := json.Unmarshal(data, &d); err != nil {
        return nil, err
    }
    switch dv := d.Items.(type) {
    case []interface{}:
        if len(dv) == 0 {
            return nil, nil
        }
    case map[string]interface{}:
        m := make(map[string]Item)
        for k, v := range dv {
            m[k] = Item(v)
        }
        return m, nil
    }
    // fallthrough return if different type, or non-empty array
    // Could have put this in a default case, but this catches non-empty arrays too
    return nil, fmt.Errorf("unexpected type in json")
}

Here's an example showing it works for both of your provided examples: https://play.golang.org/p/c0oZX2-xpN

Upvotes: 1

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