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mongodb - 为什么我的结果数组在这个 mongo 查询中返回为空？

问题描述

这是我的查询，我是 Mongo 的新手，所以我有点摸索这个查询。我的目标是让球员的队友得到供应。我将显示查询，然后显示播放器的文档。

db.Players.aggregate([{
    $match: {_id: "/players/c/cruzne02.shtml"}}, 
    {$unwind: "$teams"},
    {$unwind: "$teams.years"}, 
    {$lookup: {
        from: "Players",
        let: {team_name: "$teams.name", team_year: "$teams.years"},
        pipeline: [{
            $match: {
                $expr: {
                    $and: [
                        {$eq: ["$teams.name", "$$team_name"]},
                        {$eq: ["$teams.years", "$$team_year"]},
                    ]
                }
            },
        }],
        as: "results"
    }},
    {$unwind: {
        path: "$results",
        preserveNullAndEmptyArrays: true
    }}, 
    {$group: {
        _id: {
            team: "$teams.name",
            year: "$teams.years"
        },
        results: {
            $push: "$results"
        }
    }}, 
    {$project: {
        team: "$_id.team",
        year: "$_id.year",
        results: 1,
        _id: 0
    }}
]);

{
    "_id": "/players/c/cruzne02.shtml",
    "url": "/players/c/cruzne02.shtml",
    "name": "Nelson Cruz",
    "image": "https://www.baseball-reference.com/req/202108020/images/headshots/f/fea2f131_mlbam.jpg",
    "teams": [{
        "name": "MIL",
        "years": [2005]
    }, {
        "name": "TEX",
        "years": [2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013]
    }, {
        "name": "BAL",
        "years": [2014]
    }, {
        "name": "SEA",
        "years": [2015, 2016, 2017, 2018]
    }, {
        "name": "MIN",
        "years": [2019, 2020, 2021]
    }, {
        "name": "TBR",
        "years": [2021]
    }]
}

我可以取回该组，但结果数组始终为空。团队和年份排成一列，但结果永远不会出现。我当前的结果有空数组，我需要更改什么。

编辑：这是我的结果

[ { results: [], team: 'MIN', year: 2020 },
  { results: [], team: 'TEX', year: 2006 },
  { results: [], team: 'MIL', year: 2005 },
  { results: [], team: 'TEX', year: 2008 },
  { results: [], team: 'TBR', year: 2021 },
  { results: [], team: 'SEA', year: 2018 },
  { results: [], team: 'TEX', year: 2007 },
  { results: [], team: 'MIN', year: 2019 },
  { results: [], team: 'SEA', year: 2017 },
  { results: [], team: 'TEX', year: 2013 },
  { results: [], team: 'TEX', year: 2011 },
  { results: [], team: 'TEX', year: 2012 },
  { results: [], team: 'SEA', year: 2016 },
  { results: [], team: 'TEX', year: 2010 },
  { results: [], team: 'SEA', year: 2015 },
  { results: [], team: 'BAL', year: 2014 },
  { results: [], team: 'MIN', year: 2021 },
  { results: [], team: 'TEX', year: 2009 } ]

标签： mongodbmongodb-query

解决方案

放在$match聚合的末尾。

db.collection.aggregate([
  {
    $unwind: "$teams"
  },
  {
    $unwind: "$teams.years"
  },
  {
    $group: {
      _id: {
        team: "$teams.name",
        year: "$teams.years",
        
      },
      results: {
        $push: {
          "name": "$name",
          "id": "$_id"
        }
      }
    }
  },
  {
    $match: {
      "results.id": "/players/c/cruzne02.shtml"
    }
  }
])

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