从MongoDB集合以10块的形式加载文档的最简单方法

Question

我想创建一个创建订单的应用程序，然后将它们加载到列表中。问题是我不能一次加载所有订单。我想10乘10加载它们。

然而，这在MongoDB中看起来非常困难，因为在SQL中没有自动id。我知道如何模拟自动id，但我认为应该更容易实现此功能。

那么，给定一个MongoDB集合，如何从最新的文档开始，一直加载到最新的文档？

Answer 1

您需要按字段对文档进行排序，然后使用skip

这里有一个详细的解释：

假设您在订单收集中有这8个文档。

[
    {
        "_id": "5e390fc33285e463a0799689",
        "customer": "Max",
        "total": 10,
        "orderDate": "2020-02-04T06:31:31.311Z",
        "__v": 0
    },
    {
        "_id": "5e390fd03285e463a079968a",
        "customer": "John",
        "total": 9.2,
        "orderDate": "2020-02-04T06:31:44.190Z",
        "__v": 0
    },
    {
        "_id": "5e390fda3285e463a079968b",
        "customer": "Smith",
        "total": 11.3,
        "orderDate": "2020-02-04T06:31:54.248Z",
        "__v": 0
    },
    {
        "_id": "5e390fdf3285e463a079968c",
        "customer": "Smith",
        "total": 12.3,
        "orderDate": "2020-02-04T06:31:59.993Z",
        "__v": 0
    },
    {
        "_id": "5e390fec3285e463a079968d",
        "customer": "Jimmy",
        "total": 15.6,
        "orderDate": "2020-02-04T06:32:12.336Z",
        "__v": 0
    },
    {
        "_id": "5e390ffd3285e463a079968e",
        "customer": "Wesley",
        "total": 11,
        "orderDate": "2020-02-04T06:32:29.670Z",
        "__v": 0
    },
    {
        "_id": "5e3910163285e463a079968f",
        "customer": "Adam",
        "total": 6.1,
        "orderDate": "2020-02-04T06:32:54.131Z",
        "__v": 0
    },
    {
        "_id": "5e3910213285e463a0799690",
        "customer": "Michael",
        "total": 7.2,
        "orderDate": "2020-02-04T06:33:05.166Z",
        "__v": 0
    }
]

如果我们想将这些文档分块，我们可以编写如下示例：

router.get("/orders", async (req, res) => {
  const page = req.query.pageIndex ? +req.query.pageIndex : 1;
  const limit = req.query.pageSize ? +req.query.pageSize : 10;
  const skip = (page - 1) * limit;

  const result = await Order.aggregate([
    {
      $sort: {
        orderDate: -1
      }
    },
    {
      $facet: {
        totalRecords: [{ $count: "total" }],
        data: [{ $skip: skip }, { $limit: limit }]
      }
    }
  ]);
  res.send(result);
});

我们在查询字符串中发送pageIndex和pageSize参数，如下http://...../orders?pageIndex=1

当我们使用pageIndex=1和pageSize=3时，结果将如下所示：（如您所见，我们还返回记录总数，以便客户端可以构建分页号）

[
    {
        "totalRecords": [
            {
                "total": 8
            }
        ],
        "data": [
            {
                "_id": "5e3910213285e463a0799690",
                "customer": "Michael",
                "total": 7.2,
                "orderDate": "2020-02-04T06:33:05.166Z",
                "__v": 0
            },
            {
                "_id": "5e3910163285e463a079968f",
                "customer": "Adam",
                "total": 6.1,
                "orderDate": "2020-02-04T06:32:54.131Z",
                "__v": 0
            },
            {
                "_id": "5e390ffd3285e463a079968e",
                "customer": "Wesley",
                "total": 11,
                "orderDate": "2020-02-04T06:32:29.670Z",
                "__v": 0
            }
        ]
    }
]

当我们使用pageIndex=2和pageSize=3时，结果会是这样的：

[
    {
        "totalRecords": [
            {
                "total": 8
            }
        ],
        "data": [
            {
                "_id": "5e390fec3285e463a079968d",
                "customer": "Jimmy",
                "total": 15.6,
                "orderDate": "2020-02-04T06:32:12.336Z",
                "__v": 0
            },
            {
                "_id": "5e390fdf3285e463a079968c",
                "customer": "Smith",
                "total": 12.3,
                "orderDate": "2020-02-04T06:31:59.993Z",
                "__v": 0
            },
            {
                "_id": "5e390fda3285e463a079968b",
                "customer": "Smith",
                "total": 11.3,
                "orderDate": "2020-02-04T06:31:54.248Z",
                "__v": 0
            }
        ]
    }
]

当我们使用pageIndex=3和pageSize=3时，结果会是这样的：

[
    {
        "totalRecords": [
            {
                "total": 8
            }
        ],
        "data": [
            {
                "_id": "5e390fd03285e463a079968a",
                "customer": "John",
                "total": 9.2,
                "orderDate": "2020-02-04T06:31:44.190Z",
                "__v": 0
            },
            {
                "_id": "5e390fc33285e463a0799689",
                "customer": "Max",
                "total": 10,
                "orderDate": "2020-02-04T06:31:31.311Z",
                "__v": 0
            }
        ]
    }
]

对于您的情况，您需要发送10作为pageSize值。