在单个查询中从 mongodb 中的 2 个集合中获取数据

我想从 2 个独立的集合中获取数据并根据date通过单个查询。这甚至可能在mongodb？我有收藏：

订单类型1

{
    "id": "1",
    "name": "Hello1",
    "date": "2016-09-23T15:07:38.000Z"
},
{
    "id": "2",
    "name": "Hello1",
    "date": "2015-09-23T15:07:38.000Z"
}

订单类型2

    {
        "id": "3",
        "name": "Hello3",
        "date": "2012-09-23T15:07:38.000Z"
    },
    {
        "id": "4",
        "name": "Hello4",
        "date": "2018-09-23T15:07:38.000Z"
    }

预期结果

[
    {
        "id": "3",
        "name": "Hello3",
        "date": "2012-09-23T15:07:38.000Z"
    },
    {
        "id": "2",
        "name": "Hello1",
        "date": "2015-09-23T15:07:38.000Z"
    },
    {
        "id": "1",
        "name": "Hello1",
        "date": "2016-09-23T15:07:38.000Z"
    },

    {
        "id": "4",
        "name": "Hello4",
        "date": "2018-09-23T15:07:38.000Z"
    }
]

现在，我想获取两种类型的orders在按日期排序的单个查询中。

您可以尝试使用 mongodb 进行以下聚合3.6及以上，但我认为您应该使用两个查询，因为对于大数据集$lookup https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/#lookup-multiple-joins管道将破裂BSON限制 https://docs.mongodb.com/manual/reference/limits/ of 16mb。但这也取决于你的$match条件或$limit。如果它们被应用到$lookup https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/#lookup-multiple-joins那么你的聚合就会完美地工作。

db.OrderType1.aggregate([
  { "$limit": 1 },
  { "$facet": {
    "collection1": [
      { "$limit": 1 },
      { "$lookup": {
        "from": "OrderType1",
        "pipeline": [{ "$match": { } }],
        "as": "collection1"
      }}
    ],
    "collection2": [
      { "$limit": 1 },
      { "$lookup": {
        "from": "OrderType2",
        "pipeline": [{ "$match": { } }],
        "as": "collection2"
      }}
    ]
  }},
  { "$project": {
    "data": {
      "$concatArrays": [
        { "$arrayElemAt": ["$collection1.collection1", 0] },
        { "$arrayElemAt": ["$collection2.collection2", 0] },
      ]
    }
  }},
  { "$unwind": "$data" },
  { "$replaceRoot": { "newRoot": "$data" } }
])