在 MongoDB 中使用 MutliCollection 聚合、连接进行查询

Question

我想在 MongoDb 上进行查询，例如 Select * from Person, School WHERE Person.pID == School.pID。我怎样才能在 MongoDB 上做到这一点。使用 Scrapy，我已经废弃了这个 page 并且已经有了 Collection，我想在 Collection 和 Mongoose 之间建立外键关系。我怎样才能在这个给定的例子上做到这一点？。谢谢。 （第一个集合是学校，第二个集合是人）

/* School Collection */
{
    "_id" : ObjectId("574453fb085516029132205a"),
    "involvedInst" : [ 
        "10403"
    ],
    "instID" : [ 
        "10359"
    ],
    "projID" : [ 
        "271289"
    ],
    "fSpeaker" : [],
    "pID" : [ 
        "1229134"
    ],
    "speaker" : [ 
        "Professor Dr. Georg  Reiser"
    ]
}

/* PersonCollection */
{
    "_id" : ObjectId("574453fb085516029132205a"),
    "beteiligteInstituten" : [ 
        "10403"
    ],
    "instID" : [ 
        "10359"
    ],
    "projID" : [ 
        "271289"
    ],
    "fachlicherDFGAnsprechpartner" : [],
    "pID" : [ 
        "1229134"
    ],
    "speaker" : [ 
        "Professor Dr. Georg  Reiser"
    ]
}

Answer 1

在 3.2 版中，有一个新功能可以在聚合函数中查找另一个集合。 https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/

在您的情况下，您可以像这样使用 $lookup：

db.person.aggregate([
    {$lookup:
       {
          from: "school",
          localField: "pId",
          foreignField: "pId",
          as: "person_school"
       } 
    }
])

文档将返回为

{
    "_id" : ObjectId("5745805a39c36b72fb8e34a9"),
    "beteiligteInstituten" : [
            "10403"
    ],
    "instID" : [
            "10359"
    ],
    "projID" : [
            "271289"
    ],
    "fachlicherDFGAnsprechpartner" : [ ],
    "pID" : [
            "1229134"
    ],
    "speaker" : [
            "Professor Dr. Georg  Reiser"
    ],
    "person_school" : [
            {
                    "_id" : ObjectId("5745802a39c36b72fb8e34a8"),
                    "involvedInst" : [
                            "10403"
                    ],
                    "instID" : [
                            "10359"
                    ],
                    "projID" : [
                            "271289"
                    ],
                    "fSpeaker" : [ ],
                    "pID" : [
                            "1229134"
                    ],
                    "speaker" : [
                            "Professor Dr. Georg  Reiser"
                    ]
            }
    ]
}

可以跨集合使用多个查找。

db.person.aggregate([
    {
        $lookup:
            {
            from: "school",
            localField: "pId",
            foreignField: "pId",
            as: "person_school"
        }
   },
   {
        $lookup:
            {
            from: "teacher",
            localField: "pId",
            foreignField: "pId",
            as: "person_teacher"
        }
   }
])

但您应该考虑使用嵌入式文档或文档引用。 https://docs.mongodb.com/v3.0/tutorial/model-referenced-one-to-many-relationships-between-documents/