如何列出（扩展）引用的子文档？

Question

我有两个收藏集 PRODUCT_OFFERING 和 PRODUCT_SPECIFICATION

。产品规范引用的ProductOffering子文档如何将其扩展为集合procuct_offering子文档

{
    "_id" : ObjectId("5c52a23fe077d70001c774a5"),
    "isBundle" : false,
    "isSellable" : true,
    "productSpecification" : {
        "_id" : ObjectId("5c51b969e077d70001c7749a"),
        "version" : "",
        "href" : "http://127.0.0.1:8189/catalogManagement/productSpecification/5c51b969e077d70001c7749a",
        "name" : "CAPTUR Outdoor",
        "@referredType" : "ProductSpecification"
    },
    "agreement" : []
}