如何限制在MongoDB中返回嵌套数组场

Question

这里的课程集合：

{ 
    "_id": "RtPA6Cxs3fzJcGpgP", 
    "Seasons": [ 
    { 
     "title": "intro", 
     "Episodes": [ 
     { 
      "title": "what is c++?", 
      "length": "12:52", 
      "free_url": "free-episode-1.mp4" 
     }, 
     { 
      "title": "why c++?", 
      "length": "05:20", 
      "paid_url": "premium-episode-1.mp4" 
     } 
     ] 
    }, 
    { 
     "title": "first season", 
     "Episodes": [ 
     { 
      "title": "declare variables", 
      "length": "12:35", 
      "paid_url": "premium-episode-2.mp4" 
     }, 
     { 
      "title": "pointers", 
      "length": "04:00", 
      "free_url": "free-episode-2.mp4" 
     } 
     ] 
    } 
    ] 
} 

我试图让（一切，除了paid_url S）：

{ 
    "_id": "RtPA6Cxs3fzJcGpgP", 
    "Seasons": [ 
    { 
     "title": "intro", 
     "Episodes": [ 
     { 
      "title": "what is c++?", 
      "length": "12:52", 
      "free_url": "free-episode-1.mp4" 
     }, 
     { 
      "title": "why c++?", 
      "length": "05:20" 
     } 
     ] 
    }, 
    { 
     "title": "first season", 
     "Episodes": [ 
     { 
      "title": "declare variables", 
      "length": "12:35" 
     }, 
     { 
      "title": "pointers", 
      "length": "04:00", 
      "free_url": "free-episode-2.mp4" 
     } 
     ] 
    } 
    ] 
} 

尝试了这些疑问： 1.这适用于客户端（镀铬控制台），但它不适用于“流星芒戈”：

db.courses.find({_id: "RtPA6Cxs3fzJcGpgP"}, {fields: {"Seasons.Episodes.paid_url": 0}}).fetch() 

我得到的 “流星蒙戈” 错误：

“$ ERR”：“无法规范化查询：不支持的badValue投影选项：字段：{$四季情节$ paid_url：。0.0} “`

尝试这样做太：

Courses.find({_id: this.params.id}, {fields: {"Seasons.$.Episodes.$.paid_url": 0}}); 

Answer 1

这是正确的查询：

db.courses.find({_id: "RtPA6Cxs3fzJcGpgP"}, {"Seasons.Episodes.paid_url": 0}}) 

无需领域的