Develop Reference

MongoDB auto updates between posts and comments vice versa

I am building a web application, and I am spending so long time to take care of updates between related documents.
For example, I have 'Task' document and 'User' document. When task is made, multiple users will be assigned to it. Thus,
taskA.assigned = ["1321231fsdfsdf"(userA's _id), "12312313asdasdasd"(userB's _id)]
userA.tasks = [..., "1231321"(taskA's _id),...]
userB.tasks = [..., "12313211"(taskB's _id),...]
I could handle it well when it comes to just creating tasks. However, it becomes too tricky when I am going to edit tasks. If user B is deleted from taskA, I have to delete userB's id and go to the userB's tasks property and delete taskA's id too.
Is there any shortcut and automatic way to deal with it? Thank you for your time to read it. Let me know if I was too vague, I will add more detail.

In a relational database like MySQL using foreign keys and cascade updates could be done automatically, but in MongoDB that's not possible.
But I see in the tags you are using Moongose, so using a post save hook could do the trick. You can set a hook that updates automatically the user collection each time a task is updated, or viceversa.
Other option would be changing your data estructure, but this depends on your case, there are some facts to take into account. I think we don't have enough information to judge, but there are many resources speaking about data normalization in MongoDB, you can check for example the official MongoDB manual.

I found a way to do this easily and with less lines of codes. Around 100 lines reduced to around 30 lines by doing this.
Long story short, I used 'update()' method and various mongo operators, such as $in, $push, or $pull.
Here is my final codes that are optimized with use of update method.
var edit = req.body;
edit.assignedTo = edit.assignedTo.split(',');
var old = req.task;
var idQueries = edit.assignedTo.map(function (x) {
return mongoose.Types.ObjectId(x);
});
User.update({tasks: old._id}, {$pull: {tasks: old._id}}, {multi: true}, function () {
// Update to remove original task's id from users assigned to it.
User.update({_id: {$in: idQueries}}, {$push: {tasks: old._id}}, {multi: true}, function () {
// Update to add edited tasks'id to new users assigned to it.
old.lastAction = 'edited';
old.edited = true;
old.editedAt = Date.now();
old.titke = edit.title;
old.desc = edit.desc;
old.dueBy = edit.dueBy;
old.assignedTo = edit.assignedTo;
old.save(function (err, task) {
if (err) return next(err);
User.populate(task, 'assignedTo', function (err, task) {
res.json(task);
});
});
});
});
Wish this help some people!

How to query firebase for many to many relationship?

It is my first time developing a SPA, and I am not using JS frameworks like React, Vue or Angular. My project just uses the firebase sdk and jquery to access the DOM elements.
In my app, the users can be associated with projects. Since that, I have a user-projects and project-users paths to represent that relationship.
When a user logs in my app I request users/uid to get the user data. After that I have to fetch the projects associated with the user. I will take the ids of the associated projects to finally request the data of each project.
I'm trying to use promises as described here, but I get nothing in the console.
function loadUserProjects() {
// Authenticated user
var user = firebase.auth().currentUser;
// General reference to the real time db
var ref = firebase.database().ref();
// Request the user data
ref.child('users/'+user.uid).on('value').then(function(snapshot) {
var user_data = snapshot.val(); console.log(user_data);
// Global variable to store the id of the selected project
project_selected_key = user_data.project_selected;
// Get the list of associated projects
return ref.child('user-projects/'+user.uid).on('value').then(function(snapshot) {
console.log(snapshot);
return snapshot;
});
}).then(function (projectsSnapshot) {
console.log(projectsSnapshot);
// List associated projects
var project_options = '';
projectsSnapshot.forEach(function (e) {
project_options += '<option value="'+e.key+'">'+e.val()+'</option>';
});
if (! project_options) {
project_options = '<option disabled selected value>- Ningún proyecto -</option>';
}
$('#project_selected').html(project_options);
}, function(error) {
// Something went wrong.
console.error(error);
});
}
I know that I have to use one additional request, because at this point the <select>will be populated with truevalues (the additional request have to query the full data of each project). But I am not getting messages in the console.
Thanks in advance.
After that, I need to define different levels of privilege in each project, and associate a level when a project is assigned to a specific user. Initially I was very excited about the real time, but it seems that firebase is getting more complicated than I supposed.

A Firebase on() listener can respond to multiple events. A promise can only resolve once, that's why it's only available when you use Firebase's once() operation.
return ref.child('user-projects/'+user.uid).once('value');

Adding a filter inside a beforeRemote remote hook

I have a problem I can't find an answer to in Loopback's docs.
Say I have a model Company and a modelEmployee. There is an 1Xn relation between the Company and its Employees. When /api/Employees is called, server returns all the employees.
I only want to return the list of employees who are in the same company with the user requesting the list.
For this, I created a remote hook
Employee.beforeRemote('find', function(context, modelInstance, next) {
var reject = function() {
process.nextTick(function() {
next(null, false);
});
};
// do not allow anonymous users
var userId = context.req.accessToken.userId;
if (!userId) {
return reject();
}
//I get the details of the user who sent the request
//to learn which company does he belong to
Employee.findById(userId, function(err, user) {
if(!context.req.query.filter) context.req.query.filter={};
context.req.query.filter.where = {brandId:user.companyId};
console.log(context.req.query);
next();
});
});
I thought this should work every time, but appearantly it only works when find already has some query filters like include - although the console.log prints a correct context.req.query object.
What am I missing? Any help would be greatly appreciated!

context.args.filter seems to work for this purpose.
As a side note, instead of replacing where, you might want to merge it with something provided by client. For implementation idea you can refer to: https://github.com/strongloop/loopback-datasource-juggler/blob/master/lib/utils.js#L56-L122

Add a new field to a document mongodb

I am very new to mongodb and have a basic question that I am having trouble with. How do I get the ID field of a document that has already been created? I need the ID so i can update/add a new field to the document.
//newProfile is an object, one string it holds is called school
if(Schools.find({name: newProfile.school}).fetch().length != 1){
var school = {
name: newProfile.school
}
Meteor.call('newSchool', school);
//Method 1 (doesn't work)
var schoolDoc = Schools.findOne({name: newProfile.school});
Schools.update({_id: schoolDoc._id}, {$set: {enrolledStudents: Meteor.user()}});
//Method 2?
//Schools.update(_id: <what goes here?>, {$push: {enrolledStudents: Meteor.user()}});
}
else {
//Schools.update... <add users to an existing school>
}
I create a new school document if the listed school does not already exist. Schools need to hold an array/list of students (this is where i am having trouble). How do I add students to a NEW field (called enrolledStudents)?
Thanks!

I'm having some trouble understanding exactly what you're trying to do. Here's my analysis and understanding so far with a couple pointers thrown in:
if(Schools.find({name: newProfile.school}).fetch().length != 1){
this would be more efficient
if(Schools.find({name: new Profile.school}).count() != 1) {
Meteor.call('newSchool', school);
Not sure what you're doing here, unless you this will run asynchronously, meaning by the time the rest of this block of code has executed, chances are this Meteor.call() function has not completed on the server side.
//Method 1 (doesn't work)
var schoolDoc = Schools.findOne({name: newProfile.school});
Schools.update({_id: schoolDoc._id}, {$set: {enrolledStudents: Meteor.user()}});
Judging by the if statement at the top of your code, there is more than one school with this name in the database. So I'm unsure if the schoolDoc variable is the record you're after.

I believe you are having trouble because of the asynchronous nature of Meteor.call on the client.
Try doing something like this:
// include on both server and client
Meteor.methods({
newSchool: function (school) {
var newSchoolId,
currentUser = Meteor.user();
if (!currentUser) throw new Meteor.Error(403, 'Access denied');
// add some check here using the Meteor check/match function to ensure 'school'
// contains proper data
try {
school.enrolledStudents = [currentUser._id];
newSchoolId = Schools.insert(school);
return newSchoolId;
} catch (ex) {
// handle appropriately
}
}
});
// on client
var schoolExists = false;
if (Schools.findOne({name: newProfile.school})) {
schoolExists = true;
}
if (schoolExists) {
var school = {
name: newProfile.school
};
Meteor.call('newSchool', school, function (err, result) {
if (err) {
alert('An error occurred...');
} else {
// result is now the _id of the newly inserted record
}
})
} else {
}
Including the method on both the client and the server allows Meteor to do latency compensation and 'simulate' the insert immediately on the client without waiting for the server round-trip. But you could also just keep the method on the server-side.
You should do the enrolledStudents part on the server to prevent malicious users from messing with your data. Also, you probably don't want to actually be storing the entire user object in the enrolledStudents array, just the user _id.

For what you're trying to do, there is no need to get the _id. When you use update, just switch out the {_id: schoolDoc._id} with your query. Looks like using {name: newProfile.school} will work, assuming that the rest of your code does what you want it to do.
While that would work with the normal Mongo driver, I see that Meteor does not allow your update query to be anything but _id: Meteor throws throwIfSelectorIsNotId exception
First, make sure that you're pulling the right document, and you can try something like this:
var school_id = Schools.findOne({name: newProfile.school})._id;
Schools.update({_id: school_id}, { $push: { enrolledStudents: Meteor.user()}});
If that doesn't work, you'll have to do a little debugging to see what in particular about it isn't working.

mongodb getting user info for every document

I'm trying to display a forum/category. I need to get the latest posts. The problem is that I also need data on the user for each post as well as the latest reply.
db.post.find({
"inForum": forumID,
},
{
'sort': [['date', -1]]
},
function(err, cursor) {
cursor.count(function(err, count) {
cursor.skip(skip).limit(20).toArray(function(err, posts) {
var complete = _.after(nodes.length, function () {
res.send(posts)
});
// for every post get its author info and the latest post info
posts.forEach(function (post) {
var users = _.pluck(posts, 'user');
user.load(users, function (profiles) {
_.each(posts,
function(post, k) {
if (profiles[post.user]) post.fieldAvatar = profiles[post.user].fieldAvatar;
});
if (post.latestReply) {
post.load(post.latestReply.id, function (latestReply) {
if (latestReply) post.latestReply = latestReply
complete()
})
}
else {
complete()
}
})
})
});
})
})
This is what I'm doing and it seems really slow / really inelegant to me. Am I doing this correctly and is there any advice for speeding this up?
Thanks.

The best thing you should do here is to embed some information for the author of the posts (username & email or avatar) into those posts so that you don't make multiple queries to the database, one should suffice (sure you have some duplicate data, but the performance is optimal).
If you don't want to / can't do that you can also modify your second query to find all authors in [array_of_ids_of_the_posts]. That would reduce your [number_of_posts] queries into only one.

You could use some caching. For example you could save the users in an dictionary during the loop so you only have to fetch it on the first occurrence from mongodb.
Maybe you could create some kind of thread model where you save basic information about the containing posts, so you only have to go through the threads.
You could save the result of the function and delete it when a new post is added .. so won't go through all posts on every call.
You should not use a document storage like a sql database. Maybe it is better to generate the forum page directly when a post is created/edited and save the whole data in a document, so you only have to make one read call to mongo to show it.