向 MongoDB 中的 $lookup 结果添加一个字段

我正在尝试使用 node.js MongoDB 驱动程序向查找结果添加一个字段。用户有两种提要 1. 他或她自己的提要和 2. 共享提要。所以我需要同时获得两者，然后将它们结合起来。这是我原来的查询，效果很好：

client.db('atlas').collection('users').aggregate([
    { $match: { user_id: userId } },
    {
      $lookup: {
        from: 'feeds',
        localField: "user_id",
        foreignField: "user_id",
        as: "feeds"
      }
    },
    {
      $lookup: {
        from: 'shares',
        localField: 'email',
        foreignField: "share",
        as: "shares"
      }
    },
    {
      $lookup: {
        from: 'feeds',
        localField: 'shares.feed_id',
        foreignField: "_id",
        as: "shared_feeds"
      }
    },
    {
      $addFields: { 'shared_feeds.share': true }
    },
    {
       $project: {
         user_id: 1,
         first_name: 1,
         last_name: 1,
         email: 1,
         feeds: { $concatArrays: [ '$feeds', '$shared_feeds' ] }
       }
    }
])

但我想在“提要”的第二次查找中添加一个字段，因此我尝试使用如下管道：

{
  $lookup: {
    from: 'feeds',
    let: { shareId: '$shares.feed_id' },
    pipeline: [
      { $match: { '_id': ObjectId('$$shareId') } }
    ],
    as: "shared_feeds"
  }
}

但我无法让比赛发挥作用ObjectId。该变量似乎不起作用。我究竟做错了什么？

样本集合： 用户：

[
    {
    "_id" : ObjectId("5e970a1f797c08e70ce4e2f6"),
    "user_id" : "testuserid",
    "first_name" : "Jacopo",
    "last_name" : "Belbo",
    "email" : "[email protected] /cdn-cgi/l/email-protection"
   }
]

feeds:

 [
  {
      "_id" : ObjectId("5f29b02318ecbf0083f01f1e"),
      "name" : "test csv",
      "user_id" : "auth0|5eac6faa1cc1ac0c147b5b16",
      "type" : "feed",
      "created_at" : ISODate("2020-08-04T18:59:47.640Z"),
      "updated_at" : ISODate("2020-08-04T18:59:47.640Z")
  },
  {
    "_id" : ObjectId("5f29b05d18ecbf0083f01f1f"),
    "name" : "typtap-small",
    "user_id" : "auth0|5f1b2da0e60194003d714680",
    "url" : "http://localstack:4572/atlas/usertes",
    "type" : "feed",
    "created_at" : ISODate("2020-08-04T19:00:45.886Z"),
    "updated_at" : ISODate("2020-08-04T19:00:45.886Z")
  }
]

shares:

[
    {
    "_id" : ObjectId("5f29b07318ecbf0083f01f20"),
    "feed_id" : ObjectId("5f29b05d18ecbf0083f01f1f"),
    "share" : "[email protected] /cdn-cgi/l/email-protection",
    "type" : "share",
    "recipient" : "email",
    "created_at" : ISODate("2020-08-04T19:01:07.668Z"),
    "updated_at" : ISODate("2020-08-04T19:01:07.668Z")
}
]

In let: { shareId: '$shares.feed_id' },你正在通过ObjectId to shareId。所以你不能用ObjectId() in match阶段。当您在查找中使用管道来查找多个条件时只需使用$expr

    {
      $match: {
        $expr: {
          $eq: [
            "$$shareId",
            "$_id"
          ]
        }
      }
    }

更新1。

当你在里面使用管道时$lookup，你需要使用$expr, Refer 查找中的 $expr https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/#specify-multiple-join-conditions-with-lookup。一旦你得到输出，你就会有一个数组，所以$unwind它并进行连接。然后将其分组以避免重复。

Working 蒙戈游乐场 https://mongoplayground.net/p/JOKKv1rKCiy

Update 2

蒙戈脚本

[
  {
    $match: {
      user_id: "testuserid"
    }
  },
  {
    $lookup: {
      from: "feeds",
      localField: "user_id",
      foreignField: "user_id",
      as: "feeds"
    }
  },
  {
    $lookup: {
      from: "shares",
      localField: "email",
      foreignField: "share",
      as: "shares"
    }
  },
  {
    $unwind: {
      path: "$shares",
      preserveNullAndEmptyArrays: false
    }
  },
  {
    $lookup: {
      from: "feeds",
      let: {
        shareId: "$shares.feed_id"
      },
      pipeline: [
        {
          $match: {
            $expr: {
              $eq: [
                "$$shareId",
                "$_id"
              ]
            }
          }
        }
      ],
      as: "shared_feeds"
    }
  },
  {
    $group: {
      _id: "$_id",
      user_id: {
        $first: "$user_id"
      },
      first_name: {
        $first: "$first_name"
      },
      last_name: {
        $first: "$last_name"
      },
      email: {
        $first: "$email"
      },
      feeds: {
        $first: "$feeds"
      },
      shares: {
        $addToSet: "$shares"
      },
      shared_feeds: {
        $addToSet: "$shared_feeds"
      }
    }
  },
  {
    $addFields: {
      shared_feeds: {
        $reduce: {
          input: "$shared_feeds",
          initialValue: [],
          in: {
            $setUnion: [
              "$$this",
              "$$value"
            ]
          }
        }
      }
    }
  },
  {
    $addFields: {
      "shared_feeds.share": true
    }
  },
  {
    $project: {
      user_id: 1,
      first_name: 1,
      last_name: 1,
      email: 1,
      feeds: {
        $concatArrays: [
          "$feeds",
          "$shared_feeds"
        ]
      }
    }
  }
]