MongoDb彙總$在數組中查找外部_ids

Question

我是一個MongoDb新手。我越來越好，但還沒有專家。我試圖以一種合理的方式設置我的收藏。我想保留一些鏈接到只是_ids數組中的外部文檔以及具有_id的對象數組。

我創建了一個JSON文檔與我想的筆記充分說明什麼，我試圖做...

// (item) Character Inventory/Items collection 
[ 
    { 
     "_id": "1234", 
     "name": "Sword", 
     "descr": "Long sword, well worn, light rust", 
     "encumber": 2, 
     "del": false 
    }, 
    { 
     "_id": "1271", 
     "name": "Pouch", 
     "descr": "Small leather waist pouch, suitable for coins", 
     "encumber": 0, 
     "del": false 
    } 
] 

// (charnpcclass) Character Classes collection 
[ 
    { "_id": "2", "name": "Thief", "del": false }, 
    { "_id": "3", "name": "Cleric", "del": false } 
] 

// (charnpcalign) Character Alignments collection 
[ 
    { "_id": "3", "name": "Lawful Good", "del": false }, 
    { "_id": "4", "name": "Neutral", "del": false } 
] 

// (character) Characters collection 
[ 
    { 
     "_id": "3345", 
     "name": "Offut 'Dead Dog' Dubro", 
     "description": "Halfling, scruffy, looks homeless", 
     "align": ObjectId("4"), 
     "classes": [ 
      ObjectId("2"), 
      ObjectId("3") 
     ], 
     "carrying": [ 
      { "itemId": ObjectId("1271"), "qty":1, "where": "Sheath inside vest", "visible": false } 
      { "itemId": ObjectId("1234"), "qty":1, "where": "Sword scabbard at waist", "visible": true } 
     ], 
     "del": false 
    } 
] 

// ------------------------------------------------------------ 
// This is my MongoDb aggregation in the REST api routes 

var linkedModels = [ 
    { 
     "$match": { "del": false } 
    }, { 
     "$lookup": { 
      from: "charnpcclass", 
      localField: "classes", 
      foreignField: "_id", 
      as: "linked_classes" 
     } 
    }, { 
     "$lookup": { 
      from: "charnpcalign", 
      localField: "alignId", 
      foreignField: "_id", 
      as: "linked_align" 
     } 
    }, { 
     "$lookup": { 
      from: "item", 
      localField: "carrying.itemId", 
      foreignField: "_id", 
      as: "linked_carrying" 
     } 
    } 
]; 
db.collection('character').aggregate(linkedModels).toArray(function (err, docs) { 
    res.json(201, docs); 
    next(); 
}); 


// Query for Character, return items carrying with data from items collection 

// ------------------------------------------------------------ 
// WHAT I *WANT* IN RESPONSE... 
{ 
    "id": "3345", 
    "name": "Offut 'Dead Dog' Dubro", 
    "description": "Halfling, scruffy, looks homeless", 
    "align": "4", 
    "classes": [ 
     "2", 
     "3" 
    ], 
    "carrying": [ 
     { "itemId": "1271", "qty":1, "where": "Sheath inside vest", "visible": false } 
     { "itemId": "1234", "qty":1, "where": "Sword scabbard at waist", "visible": true } 
    ], 
    "linked_align": [ 
     { "_id": "4", "name": "Neutral" }, 
    ], 
    "linked_classes": [ 
     { "_id": "2", "name": "Thief" }, 
     { "_id": "3", "name": "Cleric" } 
    ], 
    "linked_carrying": [ 
     { "_id": "1271", "name": "Dagger", "encumber": 0 }, 
     { "_id": "1234", "name": "Sword", "encumber": 2 } 
    ] 
} 

// ------------------------------------------------------------ 
// WHAT I ACTUALLY GET IN RESPONSE 
{ 
    "id": "3345", 
    "name": "Offut 'Dead Dog' Dubro", 
    "description": "Halfling, scruffy, looks homeless", 
    "align": "4", 
    "classes": [ 
     "2", 
     "3" 
    ], 
    "carrying": [ 
     { "itemId": "1271", "qty":1, "where": "Sheath inside vest", "visible": false } 
     { "itemId": "1234", "qty":1, "where": "Sword scabbard at waist", "visible": true } 
    ], 
    "linked_align": [ 
     { "_id": "4", "name": "Neutral" }, 
    ], 
    "linked_classes": [], 
    "linked_carrying": [] 
} 

，我希望你注意到的正上方，在JSON響應例的下面的問題。我的鏈接陣列是空的，我不知道如何解決這個問題。

我將不勝感激您的專家MongoDB的查詢建議:-)

Answer 1

你必須$unwind扁平化標量和子文件外國_ids，並在管道的末尾添加$group階段找回原來的結構。

$first蓄電池保持領域和$push與$arrayElemAt積累數組值調整爲$unwind

var linkedModels = [ 
    { 
     "$match": { "del": false } 
    }, 
    { 
     "$lookup": { 
      from: "charnpcalign", 
      localField: "align", 
      foreignField: "_id", 
      as: "linked_align" 
     } 
    }, 
    { 
     "$unwind":"$classes" 
    }, 
    { 
     "$lookup": { 
      from: "charnpcclass", 
      localField: "classes", 
      foreignField: "_id", 
      as: "linked_classes" 
     } 
    }, 
    { 
     "$group": { 
      "_id": "$_id", 
      "name": {"$first":"$name"}, 
      "align": {"$first":"$align"}, 
      "classes":{"$push":"$classes"}, 
      "carrying":{"$first":"$carrying"}, 
      "linked_align":{"$first":"$linked_align"}, 
      "linked_classes":{"$push":{"$arrayElemAt":["$linked_classes",0]}} 
     } 
    }, 
    { 
     "$unwind":"$carrying" 
    }, 
    { 
     "$lookup": { 
      from: "item", 
      localField: "carrying.itemId", 
      foreignField: "_id", 
      as: "linked_carrying" 
     } 
    }, 
    { 
     "$group": { 
      "_id": "$_id", 
      "name": {"$first":"$name"}, 
      "align": {"$first":"$align"}, 
      "classes":{"$first":"$classes"}, 
      "linked_align":{"$first":"$linked_align"}, 
      "carrying":{"$push":"$carrying"}, 
      "linked_carrying":{"$push":{"$arrayElemAt":["$linked_carrying",0]}} 
     } 
    } 
] 

你不會在3.4版本需要$unwind標量陣列（classes）上，你可以分別替換{"classes":{"$push":"$classes"}} & {"linked_classes":{"$push":{$arrayElemAt:["$linked_classes",0]}}}和{"classes":{"$first":"$classes"}} & {"linked_classes":{"$first":"$linked_classes"}}。