How to model and save in mongoose multi-to-multi relationship? - node.js

Question

I want to 2 model, one is user that can belongs to multiple groups, and another is group that can has multiple users.
This is my schemas and models, i don't know whether they the correct:
var Schema = mongoose.Schema;
var UserSchema = new Schema({
joinedGroups:[{type:Schema.Types.ObjectId, ref: 'Group'}]
}
);
var GroupSchema = new Schema({
createdBy: {type: Schema.Types.ObjectId, ref: 'User'},
joinedUsers:[{ type: Schema.Types.ObjectId, ref: 'User' }]
});
var User = mongoose.model('User',UserSchema);
var Group = mongoose.model('Group',GroupSchema);
when receive POST of url:/api/groups with the body of user._id, I want to join this user to new create group, besides, i want to join this new created group to user's joinedGroups and finally i want to response the client of the new group with users in it. Follow is my code of doing this:
app.post('/api/groups', function(req, res){
console.log(req.body);
var userId = req.body.user_id;
var group = {
createdBy : userId
};
Group.create(group, function(err,group){
if(err){
console.log('create group err');
res.send(err);
}
else{
console.log('create group success');
User.update({_id: userId},
{$push: {joinedGroups: group._id}},
function(err,user){
if(err){
console.log('update user err');
res.send(err);
}
else{
Group.update({_id: group._id},
{$push: {joinedUsers: user}},
function(err,group){
if(err){
console.log('update group err:' + err);
res.send(err);
}
else{
group.populate({path:'joinedUsers'},
function(err, group){
if(err){
console.log('populate group err');
res.send(err);
}
else{
console.log('populate group success');
res.json(group);
}
}
);
}
});
}
});
}
});
});
I feel it's really complex, and it occur error :
update group err:CastError: Cast to ObjectId failed for value "1" at path "joinedUsers"
So i want somebody help me with right solution to do this, thanks!
edit:
I also want to support join user in to existed group in PUT /api/group/:group_id like below:
var userId = req.body.user_id;
var groupId = req.params.group_id;
how to do that? thanks!

Answer 1

First of all, your realization is really complex and it can be simplified as this:
var userId = req.body.user_id; // this is an ObjectId
var group = {
createdBy: userId,
joinedUsers: userId
};
Group.create(group, function (err, group) {
if (err || !group) {
return res.send(err);
}
User.findById(userId, function (err, user) {
if (err || !user) {
return res.send(err);
}
user.joinedGroups.push(group._id);
user.save(function (err) {
if (err) {
return res.send(err);
}
group.populate('joinedUsers', function (err, group) {
if (err || group) {
return res.send(err);
}
res.json(group);
});
});
});
});
And the reason why you getting CastError error is: the update method returns 1 as second argument of callback if successfully updated. But your Group#joinedUsers filed expecting User reference.