合并子文档主文档与MongoDB的聚集

Question

下面是我收集的样本记录：

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

} 

下面是我在做什么：

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

而其结果是类似于：

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

不过，我想实现的是：

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

我可以使用$project操作将子文档合并到主文档中吗？

Answer 1

要重塑您的文档，您需要在管道中添加$project阶段，并使用dot notation访问子文档的字段。

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

Answer 2

这是我的方法，它是一些更接近您的预期结果。

我的样本数据

"_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" 
      } 
    ] 

执行db.collection.aggregate后（[{$开卷： “$页”}]）

"_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$组到管道

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" } } 

希望它有助于。