使用 mongo 添加两个额外的过滤器 1 collection

Question

我有 4 个 collections:

用户

users: { id: '123123123', name: 'MrMins' }

匹配

{ id: 1, team1: 23, team2: 24, date: '6/14', matchday: 1, locked: false, score1: null, score2: null }
{ id: 2, team1: 9, team2: 32, date: '6/15', matchday: 1, locked: false, score1: null, score2: null }

国家

{id: 23, country: "Russia", pais: "Rusia", group: 'A' }
{id: 24, country: "Saudi Arabia", pais: "Arabia Saudita", group: 'A' }
{id: 9, country: "Egypt", pais: "Egipto", group: 'A' }
{id: 32, country: "Uruguay", pais: "Uruguay", group: 'A' }

预测

{ matchid: 1, score1: 3, score2: 4, userid: '123123123' }
{ matchid: 2, score1: 3, score2: 0, userid: '123123123' }

我的查询：

db.collection('matches').aggregate([
    {
        $lookup: {
          from: 'countries',
          localField: 'team1',
          foreignField: 'id',
          as: 'team1'
        }
    },{
        $lookup: {
          from: 'countries',
          localField: 'team2',
          foreignField: 'id',
          as: 'team2'
        }
    }
    ]).toArray(function(err, res) {
      callback(err, res);
    });

刚才，我有matches和countries（两次）之间的关系。如何将附加过滤器添加到 forecast 与 matchid 和 userid 建立关系？

Answer 1

$lookup 用作左外连接，但它会将 "joined" 结果作为数组插入文档中。因此，您添加的每个字段（使用 as 选项）都将是一个数组。

要从 forecasts 和 users 获取数据，您必须将该数组转换为一个对象，您可以使用 $arrayElemAt 运算符：

db.matches.aggregate([
    {
        $lookup: {
          from: 'countries',
          localField: 'team1',
          foreignField: 'id',
          as: 'team1'
        }
    },{
        $lookup: {
          from: 'countries',
          localField: 'team2',
          foreignField: 'id',
          as: 'team2'
        }
    },{
        $lookup: {
          from: 'forecast',
          localField: 'id',
          foreignField: 'matchid',
          as: 'forecast'
        }
    }, {
        $addFields: {
          forecast: { $arrayElemAt: [ "$forecast", 0 ] }
        }
    },{
        $lookup: {
          from: 'users',
          localField: 'forecast.userid',
          foreignField: 'id',
          as: 'forecast.user'
        }
    }
])

Answer 2

使用嵌套管道 mongodb 3.6 $lookup 版本会非常简单

db.matches.aggregate([
  {
    $lookup: {
      from: 'countries',
      let: { 'team1': '$team1' },
      pipeline: [
        { $match: { $expr: { $eq: [ '$id', '$$team1' ] } }}
      ],
      as: 'team1'
    }
  },{
    $lookup: {
      from: 'countries',
      let: { 'team2': '$team2' },
      pipeline: [
        { $match: { $expr: { $eq: [ '$id', '$$team2' ] } }}
      ],
      as: 'team2'
    }
  }, {
    $lookup: {
      from: 'forecast',
      let: { "match_id": "$id" },
      pipeline: [
        { $match: { $expr: { $eq: [ '$matchid', '$$match_id' ] } }},
        { $lookup: {
          from: 'users',
          let: { 'userid': '$userid' },
          pipeline: [
            { $match: { $expr: { $eq: [ '$id', '$$userid' ] } }}
          ],
          as: 'user'
        }}
      ],
      as: 'forecast'
    }
  }
])

使用 mongo 添加两个额外的过滤器 1 collection

Add two extra filter of 1 collection using mongo

mongodb

mongodb-query

node-mongodb-native