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 S

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.