将数组插入mongoDB中的子子文档

Question

当值不存在时，我想在子文档的数组中插入一个值。我有一个像这样的集合

 {
    "_id" : ObjectId("57ff25a74be508216afa9e03"),

    "RTODetails" : [
        {
            "pincode" : "34tgefgef",
            "state_name" : "Assam",
            "PUCDetails" : [
                {
                    "PUC_number" : "PUC755757",
                    "puc_year" : "2016"
                }
            ]
        }
    ]
    }

我想在PUCDetails下添加另一个数组，如

{
    "_id" : ObjectId("57ff25a74be508216afa9e03"),

    "RTODetails" : [
        {
            "pincode" : "34tgefgef",
            "state_name" : "Assam",
            "PUCDetails" : [
                {
                    "PUC_number" : "PUC755757",
                    "puc_year" : "2016"
                },
                {
                    "PUC_number" : "PUC755757111",
                    "puc_year" : "2017"
                }
            ]
        }
    ]
}

我正在使用

db.collection('vehicleDetails').update(
    { "_id": new ObjectId('57ff25a74be508216afa9e03') },
    {
        $push: {
            "RTODetails.$.PUCDetails":{
                "PUC_number" : "PUC755757111",
                "puc_year" : "2017"
            }
        }
    }
)

但它不起作用。