在MongoDB中查詢嵌入文檔

Question

我有一個Bson，其中嵌入文檔遵循以下結構。我想知道如何在特定日期獲取變量的值（「2014-08-09」：53.0）或庫存值（「2014-08-09」：0.0） 。

{ 
    "_id" : , 
    "last_modified" : "", 
    "client" : "", 
    "credentials" : [], 
    "tags" : [], 
    "variables" : [ 
     { 
      "name" : "sales", 
      "_values" : { 
       "2014-08-09" : 53.0, 
       ... 
      }, 
      "tags" : [], 
      "is_target" : true, 
      "method1" : "", 
      "method2" : "", 
      "vtype" : , 
      "index_type" : 
     }, 
     { 
      "name" : "inventory", 
      "_values" : { 
       "2014-08-09" : 0.0, 
       ... 
      }, 
      "tags" : [], 
      "is_target" : , 
      "method1" : "", 
      "method2" : "", 
      "vtype" : , 
      "index_type" : 
     }, 
     { 
      "name" : "price", 
      "_values" : {}, 
      "tags" : [], 
      "is_target" : , 
      "method2" : "", 
      "method1" : "", 
      "vtype" : , 
      "index_type" : 
     } 
    } 
} 

Answer 1

嘗試使用MongoDB的總框架 https://docs.mongodb.com/manual/reference/operator/aggregation/

db.mycol.aggregate([ 
    {"$unwind":"$variables"}, 
    {$project:{"date":"$variables._values.2014-08-09"}} 
])