在mongoDB中查找嵌套文档？

Question

这是一个MongoDB的结构：

-users

--articles

---标签

**Collection** 
user: 
[ 
    { 
     _id : ID, 
     username : "u1", 
     articles: 
     [ 
      {_id : ID,title:"",url: "",tags:["a", "b", "c"]}, 
      {_id : ID,title:"",url: "",tags:["a1", "b1", "c3"]}, 
      ... 
     ] 
    }, 
    { 
     _id : ID, 
     username : "u2", 
     articles: 
     [ 
      {title:"",url: "",tags:["a3", "b3", "c3"]}, 
      {title:"",url: "",tags:["a4", "b4", "c3"]}, 
      ... 
     ] 
    } 
] 

如何寻求“C3所有文章“所有用户的标签？

Answer 1

假设您的收藏包含都包含有标签的文章文件：

db.collection.find({articles.tags: "c3"}, {articles: 1})