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[
{
"operation": "shift",
"spec": {
"rating": {
"*": { // 匹配“rating”以下的所有key
"$": "ratings" // 将每个“key”输出到输出中的“rating”
}
]
//即输出JSON的value既可以是输入JSON的value，也可以是输入JSON的key
//在匹配到每个子键时，$捕获该键的名称本身
//$本质是键名提取器