Question

我有3个收藏集：群组，用户和成员。网上论坛集合包含网上论坛的详细信息，用户集合包含特定于用户的详细信息和成员集合包含用户与组的关联。

例如：

Groups:

id                                      |   name 
ObjectId("5ee5e346fae4a21e28a81d91")    |   Housemates 
ObjectId("5ee5e346fae4a21e28a81d92")    |   Co-workers


Users:

id                                      |   name
ObjectId("5ee493b0989d0f271cdc41c1")    |   Joulie
ObjectId("5ee493b0989d0f271cdc41c3")    |   Newelle
ObjectId("5ee493b0989d0f271cdc41c5")    |   John
ObjectId("5ee493b0989d0f271cdc41c7")    |   Larry

Members:
group_id                                | user_id  
ObjectId("5ee5e346fae4a21e28a81d91")    | ObjectId("5ee493b0989d0f271cdc41c1")
ObjectId("5ee5e346fae4a21e28a81d91")    | ObjectId("5ee493b0989d0f271cdc41c3")
ObjectId("5ee5e346fae4a21e28a81d92")    | ObjectId("5ee493b0989d0f271cdc41c5")
ObjectId("5ee5e346fae4a21e28a81d92")    | ObjectId("5ee493b0989d0f271cdc41c7")

我想加入这三个集合，并使用组名获取每个组的用户详细信息。

   Expected Output:
    [
        { "group_name":"Housemates", 
          "user_info": [
            {"name":"Joulie"},
            {"name":"Newelle"}
            ]
        },
        { "group_name":"Co-workers", 
          "user_info": [
            {"name":"John"},
            {"name":"Larry"}
            ]
        }
   ]

我编写了一个查询以获取如上所述的输出，但是它不起作用：

db.members.aggregate([
      {
        $lookup : {
          from: 'users',
          localField: "user_id",
          foreignField: "_id",
          as: "user_info"
        }
      },{
        $lookup: {
            from: 'groups',
            localField: "group_id",
            foreignField: "_id",
            as: "group_info"
        }
      }
    ]);

This这个问题看起来很相似，我也尝试过该解决方案，但是它似乎对我不起作用。我将不胜感激任何帮助或指导。预先谢谢你！

Answer 1

您有一个正确的想法，我们只需要在查找后重建数据即可：

db.members.aggregate([
  {
    $lookup: {
      "from": "groups",
      "localField": "group_id",
      "foreignField": "_id",
      as: "groups"
    }
  },
  {
    $lookup: {
      "from": "users",
      "localField": "user_id",
      "foreignField": "_id",
      as: "users"
    }
  },
  {
    $unwind: "$groups"
  },
  {
    $unwind: "$users"
  },
  {
    $group: {
      _id: "$groups._id",
      group_name: {
        $first: "$groups.name"
      },
      user_info: {
        $addToSet: {
          name: "$users.name"
        }
      }
    }
  }
])

Mongo Playground

如何在mongodb中加入2个以上的集合？

1 个答案: