node.js Mongoose/mongoDB 查询加入.. 但我来自 sql 背景
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Mongoose/mongoDB query joins.. but I come from a sql background
提问by nwkeeley
I coming from a sql background so writing queries in sql where I join tables is quite simple but I guess I am missing that in mongoose/mongodb
我来自 sql 背景，所以在我加入表的 sql 中编写查询非常简单，但我想我在 mongoose/mongodb 中缺少它
Basically I know the Subscriber_ID (which maps to a document in the User Collection)
基本上我知道 Subscriber_ID （它映射到用户集合中的文档）
I want to pull the project group, with all the projects that the user belongs to so if I was to write this in pseduo sql it would be like
我想拉出项目组，以及用户所属的所有项目，所以如果我在 pseduo sql 中编写它，它会像
Select
ProjectGroup.title,
Project.Title
FROM
ProjectGroup,
Project,
User
WHERE
User.id = req.body.subscriber_id
AND Project.subscriber_id = User.id
AND ProjectGroup.project_id = Project.id
There must be a way to do similiar joins in mongoose/mongodb because the type is mapping to a schema right?
必须有一种方法可以在 mongoose/mongodb 中进行类似的连接，因为类型映射到模式对吗？
My Schemas.....
我的架构.....
Project Group Schema
项目组架构
var ProjectGroupSchema = new Schema({
title : String
, projects : [ { type: Schema.Types.ObjectId, ref: 'Project' } ]
});
Project Schema
项目架构
var ProjectSchema = new Schema({
title : {type : String, default : '', required : true}
, subscribers : [{ type: Schema.Types.ObjectId, ref: 'User' }]
});
User Schema
用户架构
var UserSchema = new Schema({
first_name : {type: String, required: true}
, last_name : {type: String, required: true}
});
Thank you!
谢谢！
回答by Michael Yin
You are just one step away!
你只差一步之遥！
Project Group Schema:
项目组架构：
var ProjectGroupSchema = new Schema({
title : String
});
Project Schema:
项目架构：
var ProjectSchema = new Schema({
title : {type : String, default : '', required : true},
group : {type: Schema.Types.ObjectId, ref: 'ProjectGroup' },
_users : [{type: Schema.Types.ObjectId, ref: 'User' }]
});
User Schema:
用户架构：
var UserSchema = new Schema({
first_name : {type: String, required: true},
last_name : {type: String, required: true},
subscribing : [{type: Schema.Types.ObjectId, ref: 'Project' }]
});
Then you can do the following:
然后您可以执行以下操作：
user.findById(req.userId)
.populate('subscribing')
.exec(function(err, user){
console.log(user.subscribing);
})
Or:
或者：
project.find({
subscriber : req.userId
})
.populate('subscriber')
.populate('group')
.exec(function(err, projects){
console.log(projects);
})
回答by joscas
There are no joins in Mongodb. This question I think is a good reference:
Mongodb 中没有连接。这个问题我认为是一个很好的参考：
To summarize, different strategies have to be adopted with mongodb for problems that would be addressed via joins in relational DBs. I would say you mainly end-up doing one of these two things:
总而言之，对于通过关系数据库中的连接解决的问题，mongodb 必须采用不同的策略。我会说你主要是做以下两件事之一：
- Embedding: You embed information in a single document that would in a relational DB be distributed amongst different tables.
- Joining information client-side: When you need to use information from several places, you query many times and then put the pieces together in your client.
- 嵌入：您将信息嵌入到单个文档中，该文档将在关系数据库中分布在不同的表中。
- 加入信息客户端：当您需要使用来自多个地方的信息时，您可以多次查询，然后在您的客户端中将这些碎片放在一起。
