Mongoose/mongoDB query joins.. but I come from a sql background

Question

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

Basically I know the Subscriber_ID (which maps to a document in the User Collection)

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

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?

My Schemas.....

Project Group Schema

var ProjectGroupSchema = new Schema({
    title             : String
  , projects          : [ { type: Schema.Types.ObjectId, ref: 'Project' } ]
});

Project Schema

var ProjectSchema = new Schema({
    title         : {type : String, default : '', required : true}
  , subscribers   : [{ type: Schema.Types.ObjectId, ref: 'User' }]
});

User Schema

var UserSchema = new Schema({
    first_name    : {type: String, required: true}
  , last_name     : {type: String, required: true}
});

Thank you!

Answer 1

You are just one step away!

Project Group Schema:

var ProjectGroupSchema = new Schema({     title             : String }); 

Project Schema:

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:

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:

user.findById(req.userId)      .populate('subscribing')      .exec(function(err, user){           console.log(user.subscribing);      }) 

Or:

project.find({         subscriber : req.userId       })      .populate('subscriber')      .populate('group')      .exec(function(err, projects){           console.log(projects);      }) 

Answer 2

There are no joins in Mongodb. This question I think is a good reference:

MongoDB and "joins"

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:

• 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.