MongoDb $ lookup查询具有对象数组中的多个字段 [英] MongoDb $lookup query with multiple fields from objects array

问题描述

此问题先前已被标记为 该问题 我可以肯定地确认它不是。

This question has previously been marked as a duplicate of this question I can with certainty confirm that it is not.

这不是链接问题的重复，因为所讨论的元素不是数组而是作为字段嵌入到数组的各个对象中。我完全知道链接问题中的查询应该如何工作，但是这种情况与我的情况不同。

This is not a duplicate of the linked question because the elements in question are not an array but embedded in individual objects of an array as fields. I am fully aware of how the query in the linked question should work, however that scenario is different from mine.

我对有疑问$ lookup 查询MongoDb。我的数据结构如下：

I have a question regarding the $lookup query of MongoDb. My data structure looks as follows:

我的事件 集合包含以下单个文档：

My "Event" collection contains this single document:

{
   "_id": ObjectId("mongodbobjectid..."),
   "name": "Some Event",
   "attendees": [
        {
           "type": 1,
           "status": 2,
           "contact": ObjectId("mongodbobjectidHEX1")
        },
        {
           "type": 7,
           "status": 4,
           "contact": ObjectId("mongodbobjectidHEX2")
        }
    ]
}

我的联系人 集合包含以下文档：

My "Contact" collection contains these documents:

{
    "_id": ObjectId("mongodbobjectidHEX1"),
    "name": "John Doe",
    "age": 35
},
{
    "_id": ObjectId("mongodbobjectidHEX2"),
    "name": "Peter Pan",
    "age": 60
}

我想做的是总计 qu在事件 集合上使用 $ lookup 运算符进行操作，并获得带有完整联系人数据的以下结果：

What I want to do is perform an aggregate query with the $lookup operator on the "Event" collection and get the following result with full "contact" data:

{
   "_id": ObjectId("mongodbobjectid..."),
   "name": "Some Event",
   "attendees": [
        {
           "type": 1,
           "status": 2,
           "contact": {
              "_id": ObjectId("mongodbobjectidHEX1"),
              "name": "John Doe",
              "age": 35
           }
        },
        {
           "type": 7,
           "status": 4,
           "contact": {
              "_id": ObjectId("mongodbobjectidHEX2"),
              "name": "Peter Pan",
              "age": 60
           }
        }
    ]
}

我对另一个文档中引用的联系人的单个元素执行了相同的操作，但是从未嵌入到数组中。我不确定要传递哪个管道参数来获得上面显示的结果？

I have done the same with single elements of "Contact" referenced in another document but never when embedded in an array. I am unsure of which pipeline arguments to pass to get the above shown result?

我还想添加一个 $ match 查询管道以过滤数据，但这并不是我真正的问题。

I also want to add a $match query to the pipeline to filter the data, but that is not really part of my question.

推荐答案

试试这个

 db.getCollection('Event').aggregate([{ "$unwind": "$attendees" },
        { "$lookup" : { "from" : "Contact", "localField" : "attendees.contact", "foreignField": "_id", "as" : "contactlist" } },
        { "$unwind": "$contactlist" },
         { "$project" :{
                    "attendees.type" : 1,
                    "attendees.status" : 1,
                    "attendees.contact" : "$contactlist",
                      "name": 1, "_id": 1
                       }
        },
        {
            "$group" : {
                _id : "$_id" ,
                "name" : { $first : "$name" }, 
                "attendees" : { $push : "$attendees" }
            }
        }
        ])

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