如何在 mongodb 中填充查找结果？

Question

我有一个评论模型，它的一部分看起来像这样：

const CommentSchema = mongoose.Schema({
    userId: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'user',
    },
    contentId: {
        type: String,
    },
    repliedTo: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'comment',
    },
    text: {
        type: String,
        required: true,
    }
});

module.exports = mongoose.model('comment', CommentSchema);

由于我的评论模型是指我的用户模型，这里是它的架构的一部分：

const UserSchema = mongoose.Schema({
    name: {
        type: String,
        required: true,
    },
    email: {
        type: String,
        trim: true,
        unique: 'Email already exists',
        match: [/.+\@.+\..+/, 'Please fill a valid email address'],
        required: 'Email is required',
    },
    photoUrl: {
        type: String,
    },  
    // this will be saved as hashed
    password: {
        type: String,
        required: 'Password is required',
    },
});

module.exports = mongoose.model('user', UserSchema);

当我对帖子发表评论时，会向该帖子添加新评论，但 repliedTo 字段保持为空。 当我回复评论时，它会被视为一条新评论，但这次 repliedTo 字段将引用它正在回复的 comment's _id。

因此，如果对某个内容发表了评论，并且该评论的 id 为“60e70494c3920d001c7fa6d6”，并且如果评论是作为对该评论的回复，则回复的 repliedTo 字段将为“60e70494c3920d001c7fa6d6”

现在，对于某个内容，我想找到在其上制作的 cmets 并回复每个评论；我还必须确保对评论的回复不会显示为独立评论。通过使用 MongoDB 的聚合查询的 $lookup 函数，我可以这样做，这是我的代码：

let comment = await Comment.aggregate([
            [
                {
                    $match: {
                        contentId: req.params.contentId,
                    },
                },
                {
                    $lookup: {
                        from: 'comments',
                        localField: '_id',
                        foreignField: 'repliedTo',
                        as: 'replies',
                    },
                },
                {
                    $match: {
                        repliedTo: {
                            $eq: null,
                        },
                    },
                },
            ],
        ]);
    
const populateQuery = [
            {
                path: 'userId',
                select: '_id name photoUrl',
            },
            
        ];
        
comment = await Comment.populate(comment, populateQuery);

结果：

[
  {
    "_id": "60e70494c3920d001c7fa6d6",
    "text": "This is nice ",
    "contentId": "60c3eda65d90e20008cab22a",
    "userId": {
      "_id": "60b74eea3907f4001c28745c",
      "name": "Meet",
      "photoUrl": "https://images.unsplash.com/photo-1509042239860-f550ce710b93?ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&ixlib=rb-1.2.1&auto=format&fit=crop&w=634&q=80"
    },
    "__v": 0,
    "replies": [
      {
        "_id": "60e705e6c3920d001c7fa6de",
        "text": "I also think this is nice ",
        "contentId": "60c3eda65d90e20008cab22a",
        "userId": "609bf455fcf4e0001c95da59",
        "repliedTo": "60e70494c3920d001c7fa6d6",
        "__v": 0
      },
      {
        "_id": "60e7066fc3920d001c7fa6e4",
        "text": "Yes you are right ",
        "contentId": "60c3eda65d90e20008cab22a",
        "userId": "60b70b79585b8b001c93cdb0",
        "repliedTo": "60e70494c3920d001c7fa6d6",
        "__v": 0
      },
      {
        "_id": "60e7069ac3920d001c7fa6ec",
        "text": "I agree with you all! ",
        "contentId": "60c3eda65d90e20008cab22a",
        "userId": "60b74eea3907f4001c28745c",
        "repliedTo": "60e70494c3920d001c7fa6d6",
        "__v": 0
      }
    ]
  },
  {
    "_id": "60e704a4c3920d001c7fa6dc",
    "text": "This is just more than nice ",
    "contentId": "60c3eda65d90e20008cab22a",
    "userId": {
      "_id": "60b74eea3907f4001c28745c",
      "name": "Meet",
      "photoUrl": "https://images.unsplash.com/photo-1509042239860-f550ce710b93?ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&ixlib=rb-1.2.1&auto=format&fit=crop&w=634&q=80"
    },
    "__v": 0,
    "replies": []
  }
]

从结果中可以看出，每个 comment 中的 userId 都填充了 _id 名称和 photoUrl 但在我的 replies 数组中，userId 只有 _id。

我需要在每个 comment 的 replies 数组中用 _id 名称和 photoUrl 填充 userId p>

我尝试了很多方法，但找不到解决方案。

请帮我找到解决这个问题的方法。

非常感谢。

Answer 1

我能够找到解决问题的方法。我在这里分享它，以防将来有人遇到同样的问题：

let comment = await Comment.aggregate([
            [
                {
                    $match: {
                        contentId: req.params.contentId,
                    },
                },
                {
                    $lookup: {
                        from: 'comments',
                        localField: '_id',
                        foreignField: 'repliedTo',
                        as: 'replies',
                    },
                },
                {
                    $match: {
                        repliedTo: {
                            $exists: false,
                        },
                    },
                },
                {
                    $lookup: {
                        from: 'users',
                        let: { replies: '$replies' },
                        pipeline: [
                            { $match: { '$expr': { '$in': ['$_id', '$$replies.userId'] } } },
                            { $project: { _id: 0, userId: { _id: '$_id', name: '$name', photoUrl: '$photoUrl' } } }
                        ],
                        as: 'replyUsers',
                    }
                },
                {
                    $project: {
                        _id: 1,
                        createdAtTime: 1,
                        contentId: 1,
                        content_type: 1,
                        text: 1,
                        opinions: 1,
                        userId: 1,
                        replies: {
                            $map: {
                                input: '$replies',
                                as: "i",
                                in: {
                                    $mergeObjects: [
                                        '$$i',
                                        {
                                            $first: {
                                                $filter: {
                                                    input: '$replyUsers',
                                                    cond: { $eq: ['$$this.userId._id', '$$i.userId'] }
                                                }
                                            }
                                        }
                                    ]
                                }
                            }
                        }
                    }
                }
            ],
        ]);

        const populateQuery = [
            {
                path: 'userId',
                select: '_id name photoUrl',
            },
        ];
        // populate the needed fields
        comment = await Comment.populate(comment, populateQuery);