Meteor: display list of current users for document - javascript

I have a list of documents in meteor that only authorised users can access. It's kind of like google docs. Is there an easy way to get a list of users which are currently viewing them?
I thought of including a "currentUsers" field in my mongodb object, and push/remove users whenever users view or stop viewing the component. This feels like a strange way to do it since data is persisted and is probably prone to errors since it doesn't exactly represent users currently viewing the component at a moment in time
This stackoverflow question is kind of what I'm looking for, but the answer is a little old, and I'm not sure how to go about using sockjs either. If someone can provide a working example that will be great.
Any help is greatly appreciated!

There are several options:
DIY solution - storing data in Collection
package meteor-user-status
https://github.com/mizzao/meteor-user-status
package mrt:spy (which seems to be deprecated, but maybe you can build on top of it)
https://atmospherejs.com/mrt/spy
socket.io
https://atmospherejs.com/joncursi/socket-io-client

You can easily find that like this-
Tracker.autorun(function() {
if (Meteor.user()) {
Meteor.subscribe('userList');
}
});
More can be found from here.

Related

pouchdb or alternative where I can control how much data stored locally?

In the design stage for an app that collects large amounts of data...
Ideally, I want it to be an offline-first app and was looking to Pouchdb/Counchdb - However, the data needs to be kept for years for legal reasons, and my concern is that this is going to consume too much local storage over time.
My thoughts were:
handle sync between pouchdb and couchdb myself, allowing me to purge inactive documents from the local store without impacting the couchdb. This feels messy and probably a lot of work
Build a local store using dexie.js and completely write the sync function. It also looks hard work, but may be less as I'm not trying to mess with a sync function
Search harder :)
Conceptually, I guess I'm looking for a 'DB cache' - holding active json document versions and removing documents that have not been touched for X period. It might be that 'offline' mode is handled separate to the DB cache..
Not sure yet if this is the correct answer..
setup a filter on couchdb to screen out old documents (lets say we have a 'date_modified' field in the doc and we filter out any docs with date_modified older than one month)
have a local routine on the client that deletes documents from the local pouchdb that are older than one month ( actually using the remove() method against the local pouchdb, not updating it with _deleted:true) - from https://pouchdb.com/2015/04/05/filtered-replication.html it appears removed documents don't sync.
docs updated on the Pouchdb will replicate normally
there might be a race condition here for replication, we'll see

How to validate read and secure documents in CouchDB?

In 10 Common Misconceptions about CouchDB, Joan Touzet is asked (30:16) if CouchDB will have a way to secure/validate reads on specific documents and/or specific fields of a document.
Joan says that if someone has access to the database, he/she can access all documents in that database.
So she says that there are a few ways to accomplish that:
(30:55) Cloudant was working on field level security access. Have they implemented it yet? Is it open-sourced?
(32:10) You should create separate document in a separate database.
(32:20) Filtered replications. She mentions that it slows 'things' down. She means that the filter slows the replication, correct?
Also, according to rcouch wiki (https://github.com/rcouch/rcouch/wiki/Validate-documents-on-read), it implements a validate_doc_read function (I haven't tested it, though). Does CouchDB has anything like it?
As far as I can see, the best approach is to model the database according to my problem (one database for this, another for that, one for this person, another for that person) and do filtered replications when necessary. Any suggestions?

real time application in C# MVC

My application required to show real time data.
Here is brief idea.
User will run Import (Some add/edit/delete operation) in database. And I want to show real time Log of Import on UI.
Can you please suggest any good examples
Best if you start here: http://www.asp.net/signalr/overview/getting-started/tutorial-getting-started-with-signalr
Then based on your scenario you can proceed by this (sending updates from back-end): http://www.asp.net/signalr/overview/getting-started/tutorial-server-broadcast-with-signalr
You could use the idea from the example by invoking the events in your data access layer or similar.
Or you could search for something more suitable for your needs.

How to store documents like google docs?

I'm interested how does google docs store documents on server side because I need to create similar application.
Does it use pure RTF/ODF files or own database?
How do they make possible versioning and undo/redo feature?
If anybody have knowing according this question please share with me.
To answer you question specifically to how Google Docs works. They use a technology called
Operational Transformation
You may be able to use one of operational transformation engines listed on: https://en.wikipedia.org/wiki/Operational_transform#OT_software
The basic idea is that every operation has a context, e.g. "delete the fourth word in the fifth paragraph" or "add an input box after the button". The clients all send each other operations thru the server. The clients and server each keep their own version of the document and apply operations as they come.
When operations have overlapping contexts, there are a bunch of rules that kick in to resolve conflicts. Like you can't modify something that's been deleted, so the delete must come last in a sequence of concurrent operations on that context.
It's possible that the various clients and server will get out of sync, so you need a secondary algorithm to maintain consistency. One way would be to reload the data from the server whenever a conflict is detected.
--This is an answer I got from a professor when I asked the same thing a couple of years ago.
You should use a database. Perhaps a table storing each document revision. First, find a way to determine whether an update is significant or not. You can store minor changes client side for redo/undo, and then, either periodically or per some condition (e.g., user hits save), create a database entry per revision (you can store things like bytes changed, bytes added, bytes deleted, etc.).
Take a look at MediaWiki, which is open source, and essentially does what you're asking (i.e., take a look at their tables and code).
RTF/ODF would typically be generated, and served, when a user requests exporting the document.
Possibly, you should consider utilizing Google Drive's public API. See link for details.

CouchDB: How to change view function via javascript?

I am playing around with CouchDB to test if it is "possible" [1] to store scientific data (simulated and experimental raw data + metadata). A big pro is the schema-less approach of CouchDB: we have to be very flexible with the metadata, as the set of parameters changes very often.
Up to now I have some code to feed raw data, plots (both as attachments), and hierarchical metadata (as JSON) into CouchDB documents, and have written some prototype Javascript for filtering and showing. But the filtering is done on the client side (a.k.a. browser): The map function simply returns everything.
How could I change the (or push a second) map function of a specific _design-document with simple browser-JS?
I do not think that a temporary view would yield any performance gain...
Thanks for your time and answers.
[1]: of course it is possible, but is it also useful? feasible? reasonable?
[added]
Ah, the jquery.couch.js (version 0.9.0) provides a saveDoc() function, which could update the _design document with the new map function.
But I also tried out the query function, which uses a temporary view. Okay, "do not use this in the real product, only during development"... But scientific research is steady development, right?
Temporary views are getting cached, as I noticed, and it works well for ~1000 documents per DB. A second plus: all users (think of 1 to 3, so a big user management is quit of an overkill) can work with their own temporary view.
Never ever use temporary views. They are really only there for dev and debugging purposes. For more information, see http://wiki.apache.org/couchdb/Introduction_to_CouchDB_views (specifically the bold "NOTE").
And yes, because design documents are really just documents with special powers, you can run you GET/POST/PUT/DELETE methods on them. However, you will usually need admin privileges to do this. So, if you are allowing a client side piece of software to do that, you are making your entire database public for read/write access - this may be fine for your application, but is important to remember.
Ex., if you restrict access to your database, but put the username and password in client side javascript, then anyone can see that username and password.
Cheers.
I´ve written an helper functions for jquery.couch and design docs, take a look at:
https://github.com/grischaandreew/jquery.couch.js

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