node.js - MongoDB 外键查询

Question

我有两个集合:

用户:

• { id:"aaaaaa"年龄:19 性别:"f"}
• { id:"bbbbbb"年龄:30, 性别:"m"}

评论:

• { id:777777 , user_id:"aaaaaa", text:"一些评论数据"}
• { id:888888 , user_id:"aaaaaa", text:"一些评论数据"}
• { id:999999 , user_id:"bbbbbb", text:"一些评论数据"}

我想找到 sex=f 和 age>18 的所有评论

(我不想嵌套，因为评论集合会很大)

Answer 1

您应该在每条评论中包含用户的数据(也称为非规范化):

{ id:777777 , user: { id:"aaaaaa", age:19 , sex:"f" } , text:"some review data" }
{ id:888888 , user: { id:"aaaaaa", age:19 , sex:"f" } , text:"some other review data" }
{ id:999999 , user: { id:"bbbbbb", age:20 , sex:"m" } , text:"mome review data" }

在这里，阅读这个link on MongoDB Data Modeling :

A Note on Denormalization

Relational purists may be feeling uneasy already, as if we were violating some universal law. But let's bear in mind that MongoDB collections are not equivalent to relational tables; each serves a unique design objective. A normalized table provides an atomic, isolated chunk of data. A document, however, more closely represents an object as a whole. In the case of a social news site, it can be argued that a username is intrinsic to the story being posted.

What about updates to the username? It's true that such updates will be expensive; happily, in this case, they'll be rare. The read savings achieved in denormalizing will surely outweigh the costs of the occasional update. Alas, this is not hard and fast rule: ultimately, developers must evaluate their applications for the appropriate level of normalization.