合併子文檔主文檔與MongoDB的聚集

Question

下面是我收集的樣本記錄：

{ 
    _id:someId, 
    pages:[ 
    {id:id,field:value}, 
    {id:otherId,field:otherValue} 
    ] 

} 

下面是我在做什麼：

collection.aggregate([ 
    {$unwind:"$pages"} 
]) 

而其結果是類似於：

{ 
    _id:id, 
    pages:{id:id,field:value} 
}, 
{ 
    _id:id, 
    pages:{id:otherId,field:otherValue} 
} 

不過，我想實現的是：

{ 
    _id:id, 
    id:id, 
    field:value 
}, 
{ 
    _id:id, 
    id:otherId, 
    field:otherValue 
} 

我可以使用$project操作將子文檔合併到主文檔中嗎？

Answer 1

要重塑您的文檔，您需要在管道中添加$project階段，並使用dot notation訪問子文檔的字段。

{ "$project": { "id": "$pages.id", "field": "$pages.field" } } 

Answer 2

這是我的方法，它是一些更接近您的預期結果。

我的樣本數據

"_id" : 1, 
    "pages" : [ 
      { 
        "_id" : "a", 
        "comment" : "Have a Nice Day" 
      }, 
      { 
        "_id" : "b", 
        "comment" : "Everyday is Beautiful" 
      }, 
      { 
        "_id" : "c", 
        "comment" : "All is Well" 
      }, 
      { 
        "_id" : "d", 
        "comment" : "Nature is wonderful" 
      }, 
      { 
        "_id" : "e", 
        "comment" : "Enjoy the moment" 
      } 
    ] 

執行db.collection.aggregate後（[{$開卷： 「$頁」}]）

"_id" : 1, "pages" : { "_id" : "a", "comment" : "Have a Nice Day" } } 
"_id" : 1, "pages" : { "_id" : "b", "comment" : "Everyday is Beautiful" } } 
"_id" : 1, "pages" : { "_id" : "c", "comment" : "All is Well" } } 
"_id" : 1, "pages" : { "_id" : "d", "comment" : "Nature is wonderful" } } 
"_id" : 1, "pages" : { "_id" : "e", "comment" : "Enjoy the moment" } } 

加入$組到管道

db.collectiom.aggregate（[{$ unwind：「$ pages」}，{$ group：{_ id：「$ pages」}}]）;

"_id" : { "_id" : "e", "comment" : "Enjoy the moment" } } 
"_id" : { "_id" : "d", "comment" : "Nature is wonderful" } } 
"_id" : { "_id" : "c", "comment" : "All is Well" } } 
"_id" : { "_id" : "b", "comment" : "Everyday is Beautiful" } } 
"_id" : { "_id" : "a", "comment" : "Have a Nice Day" } } 

希望它有助於。