How can I convert JSON keys from snake_case to camelCase in Go?

Converting JSON Snake Case Keys to Camel Case Keys

In Go, snake_case keys in a JSON object can be converted to camelCase keys recursively using techniques based on Go's data structures and JSON encoding/decoding functionality.

One approach involves defining two structs that differ only in their JSON tags, enabling easy conversion between them. The following code demonstrates this:

<code class="go">package main

import (
    "encoding/json"
    "fmt"
)

type ESModel struct {
    AB string `json:"a_b"`
}

type APIModel struct {
    AB string `json:"aB"`
}

func main() {
    b := []byte(`{
            "a_b": "c"
    }`)

    var x ESModel
    json.Unmarshal(b, &x)

    b, _ = json.MarshalIndent(APIModel(x), "", "  ")
    fmt.Println(string(b))
}</code>

For more general conversion, an alternative method involves unmarshalling the JSON document into a map. If successful, key fixes can be applied and recursive calls made for each value in the map.

<code class="go">package main

import (
    "bytes"
    "encoding/json"
    "fmt"
    "strings"
)

func main() {
    b := json.RawMessage(`{
            "a_b": "c",
            "d_e": ["d"],
            "e_f": {
                    "g_h": {
                            "i_j": "k",
                            "l_m": {}
                    }
            }
    }`)

    x := convertKeys(b)

    buf := &bytes.Buffer{}
    json.Indent(buf, []byte(x), "", "  ")
    fmt.Println(buf.String())
}

func convertKeys(j json.RawMessage) json.RawMessage {
    m := make(map[string]json.RawMessage)
    if err := json.Unmarshal([]byte(j), &m); err != nil {
            return j
    }

    for k, v := range m {
            fixed := fixKey(k)
            delete(m, k)
            m[fixed] = convertKeys(v)
    }

    b, err := json.Marshal(m)
    if err != nil {
            return j
    }

    return json.RawMessage(b)
}

func fixKey(key string) string {
    return strings.ToUpper(key)
}</code>

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