MongoDB - 查找單個匹配文檔的嵌入式陣列中的第一個和最後一個

Question

我有一組網站，每個網站都包含正在跟蹤的網站及其關鍵字列表。我還有另一個名爲「排名」的集合，它對網站中的每個關鍵字都包含排名。收集到目前爲止是這樣的：

{ 
    "_id" : ObjectId("58503934034b512b419a6eab"), 
    "website" : "https://www.google.com", 
    "name" : "Google", 
    "keywords" : [ 
     "Search", 
     "Websites", 
    ], 
    "tracking" : [ 
     { 
      "_id" : ObjectId("5874aa1df63258286528598d"), 
      "position" : 0, 
      "created_at" : ISODate("2017-01-1T09:32:13.831Z"), 
      "real_url" : "https://www.google.com", 
      "keyword" : "Search" 
     }, 
     { 
      "_id" : ObjectId("5874aa1ff63258286528598e"), 
      "keyword" : "Search", 
      "real_url" : "https://www.google.com", 
      "created_at" : ISODate("2017-01-2T09:32:15.832Z"), 
      "found_url" : "https://google.com/", 
      "position" : 3 
     }, 
     { 
      "_id" : ObjectId("5874aa21f63258286528598f"), 
      "keyword" : "Search", 
      "real_url" : "https://www.foamymedia.com", 
      "created_at" : ISODate("2017-01-3T09:32:17.017Z"), 
      "found_url" : "https://google.com/", 
      "position" : 2 
     }, 

     { 
      "_id" : ObjectId("5874aa21f63258286528532f"), 
      "keyword" : "Websites", 
      "real_url" : "https://www.google.com", 
      "created_at" : ISODate("2017-01-1T09:32:17.017Z"), 
      "found_url" : "https://google.com/", 
      "position" : 1 
     }, 

     { 
      "_id" : ObjectId("5874aa21f63258286528542f"), 
      "keyword" : "Websites", 
      "real_url" : "https://www.google.com", 
      "created_at" : ISODate("2017-01-1T09:32:17.017Z"), 
      "found_url" : "https://google.com/", 
      "position" : 2 
     }, 

    ] 
} 

我想要做的是：

1）組中的所有關鍵字一起通過關鍵字

2）找到起始位置（在本月的最開始）

3）查找當前位置（今天的）

所以理論上我希望接受的對象，如：

{ 
    "_id" : ObjectId("58503934034b512b419a6eab"), 
    "website" : "https://www.google.com", 

    "tracking" : [ 
     { 
      "_id" : ObjectId("5874aa1df63258286528598d"), 
      "keyword": "Search", 
      "start_position": 0, 
      "todays_position": 3, 

     }, 

     { 
      "_id" : ObjectId("5874aa1df63258286528598d"), 
      "keyword": "Website", 
      "start_position": 0, 
      "todays_position": 2, 

     }, 


    ] 

雖然我對如何在另一個字段上進行分組感到困惑。我已經試過到目前爲止以下：

db.getCollection('websites').aggregate([ 

    { 
     $lookup: { 
      from: "seo_tracking", 
      localField: "website", 
      foreignField: "real_url", 
      as: "tracking" 
     } 
    }, 

    { 
     $match: { 
      "_id" : ObjectId("58503934034b512b419a6eab") 
     } 
    }, 

    { 
     $group: { 
      "_id" : "$_id", 
      "keyword" : { 
       $first: "$tracking.keyword", 
      }, 
     } 
    } 

]); 

但這不是由關鍵字分組，我也不能找出我將如何得到的預期值。

Answer 1

你可以嘗試這樣的事情。 $unwind跟蹤數組後跟$sort,tracking.keyword和tracking.created_at。 $group由tracking.keyword和$first得到起始位置，$avg得到平均位置，$last得到今天的位置。最終$group將所有數據彙總回tracking陣列。

db.website.aggregate([{ 
    $match: { 
     "_id": ObjectId("58503934034b512b419a6eab") 
    } 
}, { 
    $lookup: { 
     from: "seo_tracking", 
     localField: "website", 
     foreignField: "real_url", 
     as: "tracking" 
    } 
}, { 
    $unwind: "$tracking" 
}, { 
    $sort: { 
     "tracking.keyword": 1, 
     "tracking.created_at": -1 
    } 
}, { 
    $group: { 
     "_id": "$tracking.keyword", 
     "website": { 
      $first: "$website" 
     }, 
     "website_id": { 
      $first: "$_id" 
     }, 
     "avg_position": { 
      $avg: "$tracking.position" 
     }, 
     "start_position": { 
      $first: "$tracking.position" 
     }, 
     "todays_position": { 
      $last: "$tracking.position" 
     } 
    } 
}, { 
    $group: { 
     "_id": "$website_id", 
     "website": { 
      $first: "$website" 
     }, 
     "tracking": { 
      $push: { 
       "keyword": "$_id", 
       "avg_position":"$avg_position", 
       "start_position": "$start_position", 
       "todays_position": "$todays_position" 
      } 
     } 
    } 
}]);