Mongodb - 查詢對象數組，但只返回一個屬性

Question

我不認爲這是重複的，但請糾正我，如果我錯了。無論如何，我只想返回「apple」和與用戶的對象電子郵件地址相匹配的客戶成員角色。我使用$ elemMatch，但返回整個客戶對象，我只想要「成員」屬性，就是這樣。

{ 
    "_id" : ObjectId("54d24e5df2878d40192beabd"), 
    "apple" : "yes", 
    "orange" : "yes", 
    "customers" : [ 
     { 
      "name" : "Jay Smith", 
      "email" : "jaysmith@example.com", 
      "member" : "silver", 
     }, 
     { 
      "name" : "Sarah Carter", 
      "email" : "sarahcarter@example.com", 
      "member" : "gold", 
     }, 
     { 
      "name" : "Jack Whatever", 
      "email" : "jackwhatever@example.com", 
      "member" : "gold", 
     }, 
    ] 
} 

理想的結果回來是：

{ 
    "_id" : ObjectId("54d24e5df2878d40192beabd"), 
    "apple" : "yes", 
    "member" : "gold" 
} 

甚至這樣就足夠了：

{ 
    "_id" : ObjectId("54d24e5df2878d40192beabd"), 
    "apple" : "yes", 
    "orange" : "yes", 
    "customers" : [ 
     {"member" : "gold"} 
    ] 
} 

這是目前我有：

ItemsModel.find({ _id: { $in: _.pluck(user.items, 'itemId') }, active: true}, 
     {apple: 1, customers: {$elemMatch: {email: user.email}} }, 
      function(error, items) { 
       if (error) { return next(error); } 

       req.payload = {}; 
       req.payload.items = items; 
       next(); 
      }); 

任何幫助真的很感激。這甚至有可能嗎？謝謝！

Answer 1

ItemsModel.aggregate([ 
    { $unwind: '$customers' }, 
    { $match: { _id: { $in: _.pluck(user.items, 'itemId'), 'customers.email': user.email } }, 
    { $project : { _id:1 , apple:1, member:'$customers.member' }} 
], function(err, res){ 
    // rest of your code here 
}) 

會給你

{ 
    "_id" : ObjectId("54d24e5df2878d40192beabd"), 
    "apple" : "yes", 
    "member" : "gold" 
}