Add a new key-value pair to a JSON object - json

Question

I am connecting to an API which gives a rather large json payload. I need to add a key and value to the root object.Once I do ioutil.Readall from the package "net/http" the JSON is a byte array.
My goal is to just simply add to the structure and move on. As an example, the following the pretty similar to what I am doing: https://tutorialedge.net/golang/consuming-restful-api-with-go/
So how can I simply add to a JSON structure another element (key: value)?

Answer 1

If all you want to do is add a key and value to the root object and produce new JSON, and you don't care about having the data in a structure, you can unmarshal into map[string]interface{}, add your value, and then marshal again:
var m map[string]interface{}
err := json.Unmarshal(data, &m)
m["new_key"] = newValue
newData, err := json.Marshal(m)
(I'm not checking for errors, but you should do that of course.) Take a look at https://golang.org/pkg/encoding/json/ for more information about how to deal with JSON in Go.

Answer 2

Here's how you can do it in an efficient way while preserving the order of keys in the original JSON. The idea is to use json.RawMessage
// original JSON
bytes := []byte(`{"name": "Adele", "age": 24}`)
// let's try to add the kv pair "country": "USA" to it
type Person struct {
Bio json.RawMessage `json:"bio"`
Country string `json:"country"`
}
p := Person{
Bio: json.RawMessage(bytes),
Country: "USA",
}
// ignoring error for brevity
modifiedBytes, _ := json.Marshal(p)
fmt.Println(string(modifiedBytes))
Output:
{"bio":{"name":"Adele","age":24},"country":"USA"}
You can see that the ordering of original JSON is preserved, which wouldn't have been the case if you marshalled the JSON to a map[string]interface{}. This is also more efficient when you're dealing with huge JSONs since there's no reflection involved.
Complete code - https://play.golang.org/p/3hAPVbrAo_w

Answer 3

Since you have a byte data, you need to parse it and store the result in a variable that has your json structure using json.Marshal.
Then after, to add a new key value pair, you can define a new struct with the key and its data type
var variable type1
// Unmarshal the byte data in a variable
json.Unmarshall(data, &variable)
// to add a new key value you can define a new type
type type2 struct {
type1
key type
}
// and you can add
variable2 := type2{variable, newValueToAdd}

Answer 4

While deserializing & reserializing is the more "correct" approach, it may be overkill for just adding a value at the root, which can be done with simple string manipulation (really byte slice manipulation, but the semantics are similar and it's arguably easier):
data := []byte(`{"foo": 1, "bar": true}`)
ins := []byte(`, "baz": "hello"`) // Note the leading comma.
closingBraceIdx := bytes.LastIndexByte(data, '}')
data = append(data[:closingBraceIdx], ins...)
data = append(data, '}')
This is more error-prone, because it is unaware of JSON syntax entirely, but it's safe enough for most cases and for large JSON documents it is more efficient than a parse, insert, and reserialize.
Playground example: https://play.golang.org/p/h8kL4Zzp7rq

Answer 5

if you want to add key-value of json bytes to new json object, you can use json.RawMessage.
type Res struct {
Data interface{}
Message string
}
var row json.RawMessage
row = []byte(`{"Name":"xxx","Sex":1}`)
res := Res{Data:row,Message:"user"}
resBytes ,err := json.Marshal(res)
println(string(resBytes))
//print result："Data":{"Name":"xxx","Sex":1},"Message":"user"}

Answer 6

SJSON package is another way to modify JSON values.
In this example :
json:= `{
"name": {"first":"James","last":"Bond"},
"age' :40,
"license" {"Diamond","Gold","Silver"}
}`
To replace a "Diamond" with "Ultimate"
value, _ := sjson.Set(json, "license.0", "Ultimate")
fmt.Println(value)
json:= `{
"name": {"first":"James","last":"Bond"},
"age' :40,
"license" {"Ultimate","Gold","Silver"}
}`
Or to add a value "Ultimate" in the end:
value, _ := sjson.Set(json, "license.-1", "Ultimate")
fmt.Println(value)
json:= `{
"name": {"first":"James","last":"Bond"},
"age' :40,
"license" {"Diamond","Gold","Silver","Ultimate"}
}`