Mongo DB組記錄並返回所選字段

Question

我想根據特定值對文檔進行分組。我還需要選擇的鍵。

這裏是我的文檔：

{ 
    title: "Add 1", 
    userId: 1, 
    description: "this is add 1", 
    location: { 
     city: "Newyork", 
     address: "Street 1, Flat # 40" 
     }, 
    createdAt: "2015-10-20", 

    title: "Add 2", 
    userId: 1, 
    description: "this is add 2", 
    location: { 
     city: "Paris", 
     address: "Street 2, Flat # 80" 
     }, 
    createdAt: "2015-10-22", 

    title: "Add 3", 
    userId: 1, 
    description: "this is add 3", 
    location: { 
     city: "Newyork", 
     address: "Street 5, Flat # 58" 
     }, 
    createdAt: "2015-10-23" 
} 

我想組文件由location.city。我也只需要標題和位置。

以上情況應該查詢什麼？

我曾嘗試此查詢：

Adds.aggregate([ 
        { $match: { userId: params.userId } }, 
        { $group: { _id: "$location.city" } },    
       ]); 

上述查詢只返回location.city，我想要的位置&冠軍的完整的對象。

Answer 1

假設你的數據實際上是這樣的：

[ 
    { 
    title: "Add 1", 
    description: "this is add 1", 
    location: { 
     city: "Newyork", 
     address: "Street 1, Flat # 40" 
     }, 
    createdAt: "2015-10-20", 
    }, 
    { 
    title: "Add 2", 
    description: "this is add 2", 
    location: { 
     city: "Paris", 
     address: "Street 2, Flat # 80" 
     }, 
    createdAt: "2015-10-22", 
    }, 
    { 
    title: "Add 3", 
    description: "this is add 3", 
    location: { 
     city: "Newyork", 
     address: "Street 5, Flat # 58" 
     }, 
    createdAt: "2015-10-23" 
    } 
] 

你可以使用一個彙總查詢，例如：

db.adds.aggregate([ 
    { $group : 
     { 
      _id : "$location.city", 
      data : { $push : { "title" : "$title", "location" : "$location" } } 
     } 
    } 
]); 

Answer 2

userID是缺少文檔，如果您的收藏看起來像這樣你聚合函數是正確的。

{ 
    "title": "Add 1", 
    "userId": 1, 
    "description": "this is add 1", 
    "location": { 
     "city": "Newyork", 
     "address": "Street 1, Flat # 40" 
     }, 
    "createdAt": "2015-10-20" 
}, 
{ 
    "title": "Add 2", 
    "userId": 2 
    "description": "this is add 2", 
    "location": { 
     "city": "Paris", 
     "address": "Street 2, Flat # 80" 
     }, 
    "createdAt": "2015-10-22" 
}, 
{ 
    "title": "Add 3", 
    "userId": 1, 
    "description": "this is add 3", 
    "location": { 
     "city": "Newyork", 
     "address": "Street 5, Flat # 58" 
     }, 
    "createdAt": "2015-10-23" 
} 

測試使用MongoDB的控制檯

db.Adds.aggregate([ 
      { $match: { userId: 1 } }, 
      { $group: { _id: "$location.city" } } 
]); 

添加標題您的結果

db.Adds.aggregate([ 
    { $match: { userId: 1 } }, 
    { 
     $group: { 
      _id: "$location.city", 
      title: {$push: "$title"} 
     } 
    } 
]);