我正在尝试根据postType =“buy”创建前10个产品列表。我的逻辑是对postType =“buy”进行计数，并对日志集合中的前10个产品进行排序。下面是我的示例日志集合。

[
    {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "buy",
        "product": "3",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "view",
        "product": "4",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "buy",
        "product": "2",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "view",
        "product": "2",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "share",
        "product": "3",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "buy",
        "product": "2",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "buy",
        "product": "2",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "share",
        "product": "2",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "buy",
        "product": "1",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "buy",
        "product": "1",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "viewvideo",
        "product": "1",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "viewvideo",
        "product": "2",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "viewvideo",
        "product": "3",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "buy",
        "product": "4",
    },
 {
        "_id": "633dc5b761ff04e7ae8e8c0f",
        "postType": "buy",
        "product": "5",
    }
]

我的预期输出为：

[{"product":1, "count":2},{"product":2, "count":3},{"product":3, "count":1}, 
   {"product":4, "count":1},{"product":5, "count":1}
 ]

我尝试了下面的代码，但它不起作用。

{
        $project: {
          _id: 0,
          list: { $setEquals: ["$postType", "buy"] }
        }
      }

我只插入了4个产品，但实际上是10个。