如何在 mongodb 中加入 2 个以上的集合？

Question

我有 3 个集合：组、用户和成员。组集合包含特定于组的详细信息，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，并通过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"}
            ]
        }
   ]

我已经编写了一个查询来获取上述输出，但它不起作用：

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 问题看起来很相似，我也尝试了它的解决方案，但它似乎对我不起作用。我真的很感激任何帮助或指导。提前致谢！

Answer 1

你的想法是对的，我们只需要在查找后重建数据：

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？

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