如何获取嵌套文档下的所有类别？

Question

我在蒙戈分贝以下JSON对象中，有在文档中周围300对象，什么是检索所有category下ticket.seating，

{ "_id": "58a1ddcb8850c027298c4dc8", "name": "Listing 1", 
"description": "", "ticket": { 
    "amount": 2, 
    "type": "electronic", 
    "splitType": 2, 
    "seating": [ 
     { 
     "category": 1, 
     "section": 2, 
     "row": 2 
     }, 
     { 
     "category": 3, 
     "section": "uiui", 
     "row": 33 
     } 
    ] }, "metadata": { 
    "user": {}, 
    "event": {}, 
    "venue": {} }, "listingId": "aabb1cb6-4e79-4d48-9451-e5247230d397" } 

预计产量查询：

1,3

Answer 1

可以使用MongoDB Distinct功能这一点。如图样品下面

db.getCollection('collection_name').distinct("ticket.seating.category"); 

它会给你在阵列等[1,3]

Answer 2

这应该做的伎俩

db.collection.aggregate([ 
    { 
     $unwind:"$ticket.seating" 
    }, 
    { 
     $group:{ 
     _id:null, 
     category:{ 
      $push:"$ticket.seating.category" 
     } 
     } 
    } 
]) 

输出：

{ "_id" : null, "category" : [ 1, 3 ] }