如何在MongoDB中查询两个具有“一对多”关系的集合？答案

【问题标题】：How to query two collections that have a "one-to-many" relationship in MongoDB?如何在MongoDB中查询两个具有“一对多”关系的集合？
【发布时间】：2021-05-08 18:32:43
【问题描述】：

我们有两个系列：“houses”和“events”。 house 集合中的每个文档都包含一个“events”字段，其中包含一组引用事件的 id（“一对多强>”关系）。数组可以为空。

“房子”架构：

const mongoose = require('mongoose');

const Schema = mongoose.Schema;

const HouseSchema = new Schema({
  name: String,
  district: String,
  locality: String,
  date: {
    type: Date,
    default: Date.now
  },
  events: [{
    type: mongoose.Schema.Types.ObjectId,
    ref: 'Event'
  }]
});

module.exports = mongoose.model('House', HouseSchema);

“事件”架构：

const mongoose = require('mongoose');

const Schema = mongoose.Schema;

const EventSchema = new Schema({
  event: String,
  details: String,
  date: {
    type: Date,
    default: Date.now
  },
  house: {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'House'
  }
});

module.exports = mongoose.model('Event', EventSchema);

我需要同时查询“房屋”和“事件”，并找到那些具有符合所有条件的引用“事件”的“房屋”。我将提供几个查询选项。

仅使用来自“房屋”的参数进行查询。假设“houses”集合中有两个文档满足条件{"locality": "Facebook"}。结果应该是这样的：

[
  {
    "_id": "601bae8e26ed00591d571dbe",
    "name": "Facebook testing department",
    "district": "Los-Angeles",
    "locality": "Facebook",
    "events": [
      {
        "_id": "601bae8e26ed00591d571dbf",
        "event": "Testing",
        "details": "Testing software for production",
        "date": "2020-07-31T21:00:00.000Z"
      }
    ]
  },
  {
    "_id": "601bae8e26ed00591d571dbc",
    "name": "Facebook office",
    "district": "Los-Angeles",
    "locality": "Facebook",
    "events": [
      {
        "_id": "601bae8e26ed00591d571dbd",
        "event": "Conference",
        "details": "Developers conference about 12345",
        "date": "2020-07-31T21:00:00.000Z"
      }
    ]
  },
];

仅针对“事件”使用参数进行查询。假设“事件”集合中有两条记录满足条件{"event": "Conference"}。结果是：

[
  {
    "_id": "601bae8e26ed00591d571dbc",
    "name": "Facebook office",
    "district": "Los-Angeles",
    "locality": "Facebook",
    "events": [
      {
        "_id": "601bae8e26ed00591d571dbd",
        "event": "Conference",
        "details": "Developers conference about 12345",
        "date": "2020-07-31T21:00:00.000Z"
      }
    ]
  },
  {
    "_id": "601bae8e26ed00591d571dba",
    "name": "Oxford",
    "district": "London",
    "locality": "Oxford",
    "events": [
      {
        "_id": "601bae8e26ed00591d571dbb",
        "event": "Conference",
        "details": "About something",
        "date": "2020-07-31T21:00:00.000Z"
      }
    ]
  },
];

使用“房屋”和“事件”的参数进行查询。如果我们查询的条件是{"locality": "Facebook", "event": "Conference"}，那么结果应该是这样的：

[  
  {
    "_id": "601bae8e26ed00591d571dbc",
    "name": "Facebook office",
    "district": "Los-Angeles",
    "locality": "Facebook",
    "events": [
      {
        "_id": "601bae8e26ed00591d571dbd",
        "event": "Conference",
        "details": "Developers conference about 12345",
        "date": "2020-07-31T21:00:00.000Z"
      }
    ]
  },
];

我遇到过类似的情况，需要使查询比平时更复杂。但是在这里，我们需要根据参数对一个或两个集合进行查询，结果，我们应该得到带有对应查询参数的嵌套“事件”的“房屋”。我不太了解 MongoDB 聚合，希望能提供帮助。

【问题讨论】：

标签： javascript node.js mongodb mongoose aggregation-framework

【解决方案1】：

声明您的输入

let locality = req.body.locality;
let event = req.body.event;

初始化聚合管道（将 HousesModel 替换为您的 reql 模型名称）

let p = HousesModel.aggregate();

检查locality 的条件

if (locality && locality.trim()) p.match({ locality: locality });

$lookup 有管道，
将events数组声明为let
匹配表达式中的事件条件
如果事件搜索可用，则检查条件，然后放置条件

p.lookup({
  from: "events", // replace your actual collection name if this is wrong
  let: { events: "$events" },
  pipeline: [
    {
      $match: {
        $and: [
          { $expr: { $in: ["$_id", "$$events"] } },
          (event && event.trim() ? { event: event } : {})         
        ]
      }
    }
  ],
  as: "events"
});

确保事件不为空

p.match({ events: { $ne: [] } });

在管道上方执行

let result = await p.exec();

Playground

按顺序组合以上代码进行测试。

【讨论】：