Golang在MongoDB中嵌套对象 [英] Golang nested objects in MongoDB

问题描述

我目前正在研究一个允许用户对某些对象进行评分的小应用程序，我的数据库（MongoDB）结构如下所示：

 电影{
 Id int 
名称字符串
} 
演员{
 Id int 
名称字符串
年龄类型
 } 
 Movie_Actors {
电影电影
演员Actor 
} 
用户{
 Id int 
用户名字符串
密码字符串
 
 Rating {
 Id int 
 User User 
 Actor Actor 
 Rating int 
} 
  

当我想要选择中的所有 Actors Movie 小于5 等级

  // db * mgo.Database 
c：= db.C（'ratings'）
 err：= c.Find（...）
   
 
 
  type Movie struct {
 Id bson.ObjectId`_id，omitempty` 
名称字符串
 Actors [] bson.ObjectId 
} 
 
类型Actor结构{
 Id bson.ObjectId` _id，omitempty` 
名称字符串
年龄int 
评级[]评级
 NRatings int 
} 
  
这里，电影直接嵌入了演员ID，演员跟踪评分本身的分开字段中的评分数量。如果您只想运行这种单一类型的查询，则可以通过将电影直接嵌入播放其中的Actor中完全将数据模型非规范化。这将更加简化查询，但也会产生大量信息重复，并阻止您将电影作为单独的实体进行处理。        关于模式设计的文档讨论这些折衷。
 
 
 
在此设计中，您可以在电影中找到演员神奇先生福克斯使用以下方式评分少于5：
  //找到电影中的演员
 var电影
 db.C（电影）。查找（bson.M {name：Fantastic Mr. Fox}）。一个（& m）
 
 //筛选演员以查找评分少于5的人。 
 var results [] Actor 
 db.C（actors）。Find（bson.M {_ id：bson.M {$ in：m.Actors}，nratings： bson.M {$ lt：5}}）。All（& results）
 fmt.Println（results）
  
 
I'm currently working on a small application that allows users to rate certain objects, my database (MongoDB) structure looks like this
Movie {
    Id int
    Name string
}
Actor {
    Id int
    Name string
    Age int
}
Movie_Actors {
    Movie Movie
    Actor Actor
}
User {
    Id int
    Username string
    Password string
}
Rating {
    Id int
    User User
    Actor Actor
    Rating int
}
My problem begins when I want to select all Actors in a Movie where there are less than 5 Ratings
// db *mgo.Database
c := db.C('ratings')
err := c.Find(...)

解决方案
For this problem, I would denormalize your schema a little to make querying in MongoDB more natural. Looking only at the types you need for this query, you might use the following:
type Movie struct {
    Id     bson.ObjectId `_id,omitempty`
    Name   string
    Actors []bson.ObjectId
}

type Actor struct {
    Id     bson.ObjectId `_id,omitempty`
    Name     string
    Age      int
    Ratings []Rating
    NRatings int
}
Here the Movie directly embeds the Actor IDs, and the Actor keeps track of the number of ratings in a separate field from the ratings themselves. If you only wanted to run this single type of query, you could fully denormalize the data model by embedding the Movies directly into the Actors who played in them. This would simplify the query even more, but would also create a lot of duplication of information and prevent you from dealing with Movies as separate entities.

See the documentation on schema design for a discussion on these tradeoffs.

In this design, you can find the actors in the movie Fantastic Mr. Fox with fewer than 5 ratings using the following:
// Find the actors in the movie
var m Movie
db.C("movies").Find(bson.M{"name": "Fantastic Mr. Fox"}).One(&m)

// Filter the actors to find those with less than 5 ratings.
var results []Actor
db.C("actors").Find(bson.M{"_id": bson.M{"$in": m.Actors}, "nratings": bson.M{"$lt": 5}}).All(&results)
fmt.Println(results)


                        
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