要计数的 MongoDB 聚合查询

Question

我正在使用 Nodejs 和 MongoDB 以及 expressjs 和 mongoose 库以及如何在另一个库之间实现 mutual用户。这是我使用的架构。

const UsersSchema = new mongoose.Schema({
    username:        { type: String },
    email:           { type: String },
    date_created:    { type: Date },
    last_modified:   { type: Date }
});    


const FollowSchema = new Schema({
    follower:        { type: Schema.Types.ObjectId, ref: 'User', required: true },
    following:        { type: Schema.Types.ObjectId, ref: 'User', required: true },
    date_created:    { type: Date },
    last_modified:   { type: Date }
});

如何查询 Mongo？

Answer 1

你可以使用下面的聚合

db.users.aggregate([
  { "$match": { "_id": 2 }},
  { "$lookup": {
    "from": "follows",
    "let": { "id": "$_id" },
    "pipeline": [
      { "$facet": {
        "userFollows": [
          { "$match": { "$expr": { "$eq": ["$follower", "$$id"] }}}
        ],
        "myFollows": [
          { "$match": { "$expr": { "$eq": ["$follower", 1] }}}
        ]
      }},
      { "$project": {
        "matchedFollowed": {
          "$setIntersection": ["$userFollows.followed", "$myFollows.followed"]
        }
      }},
      { "$unwind": "$matchedFollowed" }
    ],
    "as": "user"
  }},
  { "$lookup": {
    "from": "follows",
    "let": { "ids": "$user.matchedFollowed" },
    "pipeline": [
      { "$match": { "$expr": { "$in": ["$follower", "$$ids"] }}}
    ],
    "as": "mutualConnections"
  }}
])