Mongoose 加入两个集合并获取两个属性中的引用数据 [英] Mongoose join two collections and get referenced data in two properties

问题描述

我正在做一个简单的关注朋友功能.

I'm doing a simple follow friend functionality.

请看下面我的代码:

以下架构:

{
 "userId": { type: String },
 "followers": [{ "followerId": type: String }],
 "followings": [{ "followingId": type: String }], 
}

用户架构:

{
 "fullName": { type: String } 
}

注意:用户 8 有 1 个关注者和 2 个关注者.

Note: user 8 has 1 follower and 2 followings.

现在，我的预期输出应该是这样的:

Now, my expected output should be like this:

        "userId": 8,
        "followers": [
            {
                "followerId": 4,
                "fullName": "Rose Marriott",
            },
            {
                "followerId": 5,
                "fullName": "James Naismith",
            }
        ],
        "followings": [
            {
                "followingId": 1,
                "fullName": "Russell Oakham",
            },
            {
                "followingId": 5,
                "fullName": "James Naismith",
            }
        ]

这是我目前尝试过的:

 db.followings.aggregate([
 { $unwind: "$followers" },
    {
        $lookup: {
            from: "users",
            localField: "followers.followerId",
            foreignField: "_id",
            as: "users"
        }
    },
    { 
        $addFields: 
        { 
            users: { $arrayElemAt: ["$users", 0] },
        },
    },
    { $unwind: "$followings" },
    {
        $lookup: {
          from: "users",
          localField: "followings.followingId",
          foreignField: "_id",
          as: "users2"
        }
    },
    { 
        $addFields: 
        { 
            users2: { $arrayElemAt: ["$users2", 0] },
        },
    },
    { $match: {"userId": mongoose.Types.ObjectId(userId) } },
    {
        $group: {
            _id: "$_id",
            userId: { $first: "$userId" },
            followers: {
                $push: {
                    followerId: "$followers.followerId",
                    fullName: "$users.fullName",
                }
            },
            followings: {
                $push: {
                    followingId: "$followings.followingId",
                    fullName: "$users2.fullName",
                }
            }
        }
      }
  ]);

但我有 2 个关注者和 2 个关注者.我想知道是什么导致了这个问题.感谢任何帮助.谢谢！

But I'm getting 2 followers and 2 followings. I wonder what's causing this issue. Appreciate any help. Thanks!

推荐答案

你可以试试，

• $addFields 生成一个名为 userIds 的唯一数组，形成数组 followers 和 followings, $setUnion 获取唯一 ID，
• $lookup 与用户集合
• $project 显示字段，
  • followers 获取 fullName、$map 以迭代 followers 循环并使用 $reduce 从用户数组中获取 followerId 的名称 和 $cond
  • followings 获取 fullName、$map 以迭代 followings 的循环并使用 $reduce 从用户数组中获取 followingId 的名称 和 $cond
  • $addFields to make a unique array called userIds form both arrays followers and followings, $setUnion to get unique ids,
  • $lookup with users collection
  • $project to show fields,
    • followers get fullName, $map to iterate loop of followers and get the name of followerId from users array using $reduce and $cond
    • followings get fullName, $map to iterate loop of followings and get the name of followingId from users array using $reduce and $cond

    db.followings.aggregate([
      {
        $addFields: {
          userIds: {
            $setUnion: [
              {
                $map: {
                  input: "$followers",
                  in: "$$this.followerId"
                }
              },
              {
                $map: {
                  input: "$followings",
                  in: "$$this.followingId"
                }
              }
            ]
          }
        }
      },
      {
        $lookup: {
          from: "users",
          localField: "userIds",
          foreignField: "_id",
          as: "users"
        }
      },
      {
        $project: {
          userId: 1,
          followers: {
            $map: {
              input: "$followers",
              as: "f",
              in: {
                $mergeObjects: [
                  "$$f",
                  {
                    fullName: {
                      $reduce: {
                        input: "$users",
                        initialValue: "",
                        in: {
                          $cond: [
                            { $eq: ["$$this._id", "$$f.followerId"] },
                            "$$this.fullName",
                            "$$value"
                          ]
                        }
                      }
                    }
                  }
                ]
              }
            }
          },
          followings: {
            $map: {
              input: "$followings",
              as: "f",
              in: {
                $mergeObjects: [
                  "$$f",
                  {
                    fullName: {
                      $reduce: {
                        input: "$users",
                        initialValue: "",
                        in: {
                          $cond: [
                            { $eq: ["$$this._id", "$$f.followingId"] },
                            "$$this.fullName",
                            "$$value"
                          ]
                        }
                      }
                    }
                  }
                ]
              }
            }
          }
        }
      }
    ])
    

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