如何在MongoDB中进行内部联接? [英] How to do inner joining in MongoDB?

问题描述

是否有可能在MongoDB中进行SQL内部联接， 好吧，我知道有

Is it possible to do SQL inner joins kind of stuff in MongoDB , well i know there is

$ lookup

$lookup

聚合管道中的属性，它等效于SQL中的外部联接，但我想执行与内部联接中类似的任务， 我有两个三个集合，需要将它们合并在一起

attribute in aggregation pipeline and it is equivalent to outer joins in SQL but i want to do a similar kind of a task as in inner joins , i have two three collections ,which i need to merge together

----User Collection----
db.User.find({})
{
   ID : 1,
   USER_NAME : "John",
   password : "pass"
}
{

   ID : 2,
   USER_NAME : "Andrew",
   PASSWORD : "andrew"
}

---ROLE COLLECTION---
db.ROLE.find({})
{
   ID : 1,
   ROLE_NAME : "admin"
},
{
    ID : 2,
    ROLE_NAME : "staff"
}

---USER_ROLE COLLECTION---
db.USER_ROLE.find({})
{
   ID : 1,
   USER_ID : 1,
   ROLE_ID : 1
}

我拥有3个以上的集合，我只想提取与用户及其角色匹配的文档，而不是全部文档，我该如何在MongoDB中进行管理?有人可以给我建议吗?

i having above 3 collections and i want extract only the documents matched with users and their respective roles not all the documents, how can i manage it in MongoDB can anyone give me a suggestion?

推荐答案

提拉米苏(Tiramisu)写道，这看起来像是架构问题.

As Tiramisu wrote this looks like schema issue.

您可以通过删除$ lookup返回空数组的文档来进行手动内部联接.

You can make a manual inner join, by removing documents where $lookup returned empty array.

....
{$lookup... as myArray},
{$match: {"myArray":{$ne:[]}}},
{$lookup... as myArray2},
{$match: {"myArray2":{$ne:[]}}},

模式改变

我个人将进行架构更新，如下所示:

I personally will go for schema update, like this:

db.User.find({})
{
   ID : 1,
   USER_NAME : "John",
   password : "pass"
   roles:[{ID : 1,  ROLE_NAME : "admin"}]
}


db.ROLE.find({})
{
   ID : 1,
   ROLE_NAME : "admin"
},

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