JSON.SET <key> <path> <value> [NX | XX]

redis> JSON.SET doc $ '{"a":2}'
OK
redis> JSON.SET doc $.a 3
OK
redis> JSON.GET doc $
"[{\"a\":3}]"

redis> JSON.SET doc $ '{"a":2}'
OK
redis> JSON.SET doc $.b 8
OK
redis> JSON.GET doc $
"[{\"a\":2,\"b\":8}]"

redis> JSON.SET doc $ '{"f1":{"a":1},"f2":{"a":2}}'
OK
redis> JSON.SET doc $..a 3
OK
redis> JSON.GET doc
"{\"f1\":{\"a\":3},\"f2\":{\"a\":3}}"

# 僅當字段不存在時寫入
redis> JSON.SET user:1 $.nickname '"neo"' NX
OK          # 第一次成功
redis> JSON.SET user:1 $.nickname '"smith"' NX
(nil)       # 條件未滿足

// 文件 main.go
package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"

	"github.com/redis/go-redis/v9"
)

var ctx = context.Background()

type Profile struct {
	Name  string `json:"name"`
	Age   int    `json:"age"`
	Tags  []string `json:"tags"`
}

func must(err error) {
	if err != nil {
		log.Fatalf("fatal: %v", err)
	}
}

func main() {
	rdb := redis.NewClient(&redis.Options{
		Addr: "localhost:6379",
	})
	defer rdb.Close()

	// ---------- 1. 寫入根文檔 ----------
	profile := Profile{Name: "Alice", Age: 27, Tags: []string{"gopher", "redis"}}
	raw, _ := json.Marshal(profile)

	if res, err := rdb.Do(ctx, "JSON.SET", "user:1001", "$", raw).Text(); err != nil {
		must(err)
	} else {
		fmt.Println("set root:", res) // OK
	}

	// ---------- 2. 更新子字段 ----------
	if res, err := rdb.Do(ctx, "JSON.SET", "user:1001", "$.age", 28, "XX").Text(); err != nil {
		must(err)
	} else if res == "" {
		fmt.Println("XX unmet, age not updated")
	} else {
		fmt.Println("update age:", res) // OK
	}

	// ---------- 3. 讀取文檔 ----------
	data, err := rdb.Do(ctx, "JSON.GET", "user:1001", "$").Result()
	must(err)
	fmt.Println("profile =", data.(string))

	// ---------- 4. 錯誤示例 ----------
	if _, err := rdb.Do(ctx, "JSON.SET", "user:1002", "$.name", "\"Bob\"").Result(); err != nil {
		fmt.Println("expected error:", err)
	}

	// Output:
	// set root: OK
	// update age: OK
	// profile = [{"name":"Alice","age":28,"tags":["gopher","redis"]}]
	// expected error: ERR new objects must be created at the root
}