在单个查询中从mongodb中的2个集合中获取数据 [英] Fetch data from 2 collections in mongodb in single query

问题描述

我想从2个独立的集合中获取数据，并通过一个查询根据日期对结果进行排序。在 mongodb 中甚至可能吗？我有收藏集：

I wanted to fetch data from 2 independent collections and sort the results based on date through a single query. Is that even possible in mongodb? I have collections:

OrderType1

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

OrderType2

    {
        "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订单在单个查询中按日期排序。

Now, I want to fetch both types of orders in a single query sorted by date.

推荐答案

您可以在mongodb 3.6 及更高版本下面尝试聚合，但我认为您应该使用两个查询因为对于大型数据集 $ lookup 管道将违反 BSON限制 为 16mb 。但这也取决于您的 $ match 条件或 $ limit 。如果将它们应用于 $ lookup 管道，那么您的聚合将可以正常工作。

You can try below aggregation with mongodb 3.6 and above but I think you should use two queries because for the large data set $lookup pipeline will breach BSON limit of 16mb. But also It depends upon your $match condition or $limit. If they are applied to the $lookup pipeline then your aggregation would work perfectly.

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" } }
])

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