如何在猫鼬$lookup后基于对象字段过滤查询

Question

我想得到一个博客的评论按顶部(率)的评论模式排序：

const CommentSchema = new Schema({
    content: {type: String, maxLength: 100, required: true},
    user: {type: Schema.Types.ObjectId, ref: 'User', required: true },
    blog: {type: Schema.Types.ObjectId, ref: 'Blog', required: true},
    reactions: [{type: Schema.Types.ObjectId, ref: 'Reaction'}],
},{ timestamps: true})

const ReactionSchema = new Schema({
    user: {type: Schema.Types.ObjectId, ref: 'User', required: true},
    comment: {type: Schema.Types.ObjectId, ref: 'Comment', required: true},
    date: {type: Schema.Types.Date, default: Date.now, required: true}
})

我的问题是：

this.model.Reaction.aggregate([            
        {
          $group: {
            _id: "$comment",
            num: { $sum: 1 }
          }
        },
        { $sort: { num: -1 } },
        {
          $lookup: {
            from: "comments",
            localField: "_id",
            foreignField: "_id",
            as: "Com",
          }
        },
        { $unwind: "$Com" },
        {
            $match: {"Com.blog": '629af177e03ab4cfe845a9a4'}
        },
        {
          $project: {
            content: "$Com.content",
            num: 1,
          }
        },
      ])

但是$match在$lookup之后是不接受的！我也尝试使用"$filter“，但是它得到了一个”数组“和一个有一个对象！我的查询不需要$match。但是需要基于blog-id对评论进行过滤。

Answer 1

你能试试这个吗

this.model.Reaction.aggregate([            
    {
      $group: {
        _id: "$comment",
        num: { $sum: 1 }
      }
    },
    { $sort: { num: -1 } },
    {
      $lookup: {
        from: "comments",
        localField: "_id",
        foreignField: "_id",
        as: "Com",
      }
    },
    { $unwind: "$Com" },
    {
        $match: {"Com.blog": mongoose.Types.ObjectId('629af177e03ab4cfe845a9a4')}
    },
    {
      $project: {
        content: "$Com.content",
        num: 1,
      }
    },
  ])