

Meteor and Qt - achipa
http://achipa.blogspot.com/2014/12/meteor-and-qt-match-made-in-heaven.html

======
jakozaur
There is a lot opinions on HNews that Meteor is too monolithic and it's bad:
[https://news.ycombinator.com/item?id=8772563](https://news.ycombinator.com/item?id=8772563)

However, that kind of projects show the opposite. It is in fact very modular.

~~~
evo_9
The fact that so many dismissed it without giving it a serious look made me
interested in seeing what it was really about. Long/short - it's an amazingly
focused, fun and easy stack to work with. I think the fact that it's easy, or
at least seems easy and probably because it's _another javascript framework_
makes it an easy target to dismiss on HN. If you are coming from a web
background like myself (aspx, ruby, etc) then it's quite a revelation how
fast, fun and easy it is to work with.

~~~
tracker1
I think that Meteor is pretty awesome, but it isn't good for a lot of use
cases out of the box... If you need really granular and flexible security
around your models, the out of the box security isn't (or wasn't last I
checked) good enough.

Common case.. GROUP_A users can read/write their own documents, but only read
other user's documents in that group... GROUP_B can read/write their own
documents as well as all documents owned by users in GROUP_A. This is a pretty
typical scenario for management chain permissions, but when I've looked ad
Meteor and similar solutions it wasn't an option (or incredibly difficult to
implement).

~~~
lourd
This is more of a data modeling and permissions question, more dependent on
the database choice rather than the framework I'd say. Since Meteor only
supports Mongo right now, I'll use Mongo terms (collections & documents)

Meteor gives you an accounts collection so you don't have to declare it
yourself. But we do need to declare the Groups Collection

    
    
        Groups = new Mongo.Collection('groups');
    

Let's assume we want Users and Groups to have a many to many relation, so each
User doc has an attribute `groups`. `groups` is an array of which each element
is the unique id of a Group document. Similarly, Group documents have an
attribute `members`, an array of which each element is a User document unique
id.

There is a third Collection needed, documents.

    
    
        Documents = new Mongo.Collection('documents');
    

Each document in the Documents Collection has an `owner` field that is the
unique id of a Group document.

To handle the security for inserting or updating the Documents Collection, you
need to set 2 allow rules on the Collection to check if the document.owner is
in the user.groups array.

    
    
        Documents.allow({
          insert: function(userId, doc) {
            // doc's owner must be one of logged in user's groups
            return Meteor.user().groups.indexOf(doc.owner) > -1;
          },
          update: function(userId, doc, field, modifier) {
            return Meteor.user().groups.indexOf(doc.owner) > -1;
          }
        }
    

As for reading the document, you do that when declaring your Publications.
Easiest would be to publish all of them, but you could also pass in a groupId
or array of groupIds if you wanted to have some restrictions.

    
    
        Meteor.publish("documents", function() {
          return Documents.find();
        };

~~~
uptownJimmy
I am not a hater, quite the contrary. I've messed around with Meteor just a
bit, and loved it. But I cannot get my head around one thing: why in the world
would anyone actually choose to use MongoDB over Postgres or MySQL ?Is there
actually a use case where a NoSQL db would be as good or preferable? Or is it
really all just a matter of people being intimidated by SQL? Because
everything informed and trustworthy that I read on the subject says that NoSQL
is simply not robust enough for doing anything more complicated than storing a
list of names and email addresses for a simple user forum. That ain't gonna
cut it for most apps.

~~~
achipa
AFAIK The reactive part is not that easy to with Mysql et al - sure, you can
hack around stored procedures, UDF and such, but it's far from being elegant.
If you "think in SQL", then of course nosql seems to make everything
difficult, but in reality, you're just taking back some of the logic and heavy
lifting from the DB server in exchange for more freedom/scalability, which may
or may not be something you want.

~~~
uptownJimmy
Thanks to all for the intelligent replies.

I 'think SQL' all day, or at least a simple subset of it, and I need to learn
more. It's paying my bills as a .NET/JavaScipt dev, you know? I'd like to
integrate it into my hobby projects. But I'm gonna watch that video linked
above and see what it sells me. I certainly don't have any innate resistance
to thinking of data as (basically) JSON arrays. I love that. We use that sorta
stuff all the time at work, passing data back and forth, to and from the core
client JavaScript functions.

I just can't shake the notion that NoSQL is so popular because SQL just is
NOT. And I get that: SQL is freaking complicated once you get to the parts
that make it so powerful. But maybe that's all a misunderstanding on my part.

------
achipa
There were some concerns as to how native this is - I'm not rendering any
HTML. The client side does use the JSON-style QML, but that's just the
declarative UI language of Qt - your high-performance code can be C++, Java,
or whatever is the native language of the platform. If you wish, though, you
can write your whole app in JavaScript, too, but that's an option, not a
requirement.

------
achipa
Hi, I'm Attila, the developer of Qondrite - the interface between Meteor and
Qt in the article. If you have any questions, feel free to ask, I'm always
looking for new perspectives, comments and will be happy to answer!

~~~
billforsternz
Really impressive work, thank you. I intend taking an in-depth look later, but
just at the moment I hope you'll indulge a more-or-less off topic question;
What tool did you use to create the youtube demo on your blog ?

~~~
achipa
I used a Chrome extension - Screencastify (
[https://www.screencastify.com/](https://www.screencastify.com/) )

~~~
billforsternz
Much appreciated, thanks.

------
jonpress
Meteor is monolithic in that it forces your app to be structured in a
particular way - It dictates how you should handle your data and how your
scripts get loaded/bundled into your app. That said, I think it's much more
flexible (and scalable - In a business sense) than a closed solutions like
Firebase. I think Meteor is suitable for most projects and monolithic isn't
always a bad thing - There is some negative stigma around the term but it's
not entirely fair. People don't go around calling Linux 'monolithic' even
though it is!

~~~
sordina
It's definitely monolithic, but depending on what you're doing it can be a
real time saver to have a lot of decisions made for you up-front.

------
dcsan
This is really interesting. I use meteor for the web, but am frustrated with
mobile html5 client clunkiness.

If i understand: \- your UI is written in QML. \- you are using Asteroid to
turn DDP protocol messages into JS events? \- are you then reactively changing
the QML markup and asking QT to re-render your UI? I'm interested how this
part works.

How granular is the reactive rendering, ie the whole page every update, or
just changed components (like reactjs DOM diffing)?

Have you dealt with other client side things like routing and page changes, or
is it currently content for QML widgets?

How far does QML allow native widgets like tab controls? Does a QML app end up
just as janky as html5?

Did you look at just having a QT application that would talk DDP? I guess QML
looks like json/markup so it's more appealing for porting an existing meteor
app, and it's markup rather than code, but some mapping to QT would presumably
give much more control?

How do you deal with client side logic? If QML is just a layout descriptor
markup, if you need actual logic client side, how do you bridge between that
and the meteor backend? I see Asteroid allows you to send data back and call
Meteor.methods. Oh I see QML actually anticipates modules in JS:
[http://doc.qt.io/qt-5/qtquick-tutorials-samegame-
samegame3-e...](http://doc.qt.io/qt-5/qtquick-tutorials-samegame-
samegame3-example.html) [http://doc.qt.io/qt-5/qtqml-modules-
topic.html](http://doc.qt.io/qt-5/qtqml-modules-topic.html)

Does QML support a webview component? In which case you could also mix in some
pages just as webviews if you didn't want to rewrite your whole app in QML?
Then again only attractive if the QT webview component uses latest chrome
renderer at an OS level, and no JS bridge was required back to your app...
that would be like a turducken anti-pattern.

Overall very interesting, thanks for sharing!

~~~
achipa
Yes, I'm using Asteroid to talk DDP/JSON with the rest of the Qt app.

In the example, I'm using models (think MVC) and updating that model, which
then automagically updates the UI.

I'm not (yet) pushing the QML via Meteor, but that is the next logical step.
Should the UI change (say, radioboxes instead of checkboxes), the plan is to
do a diff and change altered components (this should be doable as QML's format
is still close enough to JSON).

QML already has a decent set of controls
([http://doc.qt.io/qt-5/qtquickcontrols-
index.html](http://doc.qt.io/qt-5/qtquickcontrols-index.html)) but I'm working
on wrapping native components so there is full coverage of ALL components
(this was actually one of my previous posts
[http://achipa.blogspot.com/2014/11/qml-wrappers-for-
native-a...](http://achipa.blogspot.com/2014/11/qml-wrappers-for-native-
android.html))

Of course, you could write a C++ DDP lib (and on the long run, probably
should, merely for the performance boost), but asteroid and JS just made a
proof-of-concept that much easier to build.

QML is not just a layout descriptor - you can embed javascript in it. Think
about QML as HTML written in JSON, but without the HTML implied semantics.

Still, JS could also be shuttled accross the DDP connection, and could be run
or changed client-side, there is no difference between those and QML as I
mentioned above, though this is also something planned-but-not-implemented-
yet.

And finally - yes, QML has a webview component([http://doc-snapshot.qt-
project.org/qt5-5.4/qtwebengine-qmlmo...](http://doc-snapshot.qt-
project.org/qt5-5.4/qtwebengine-qmlmodule.html))

------
rattray
Wow, QML looks... really nice. Has anyone used it to deploy cross-platform
apps to iOS/Android? What was your experience? Biggest drawbacks?

~~~
Elv13
As of 2012:

* Lack of documentation about QML itself (first and third party)

* Unhandled or unsupported corner case like trees that are a pain to implement using recursive rectangles

* Very limited set of widgets (this has improved)

* Ubuntu/Blackberry/Sailfish/PlasmaActive SDK are incompatible

You can hack your way around and get back a good old imperative QPainter and
be done with it, but it kind of void the whole point.

~~~
achipa
In all honesty, Qt has come a long way since 2012 - QML is reasonably well
documented nowadays. Controls (the widget library), while not a silver bullet,
are good enough (at least on Android, haven't used iOS all that much) so
normally you don't need to go as low as your own QPainter or even Rect-s.

------
antoniuschan99
My stack uses Appcelerator, Rails, and Meteor.

Appcelerator... kind of sucks. But it's much better than HTML5. It performs
much better than HTML5, but I find it very hard to write. There's just way too
much quirkiness and hacks to make it work. The only thing I like about it is
that it's written in JavaScript (but it would be fun to learn a new one).

How does QT compare in this regard?

~~~
achipa
Performance-wise Qt is quite good, but still comes up a bit short on the
Widget quality and consistency side - this is where project like my native
component-wrappers come in to the story (shameless plug -
[http://achipa.blogspot.com/2014/11/qml-wrappers-for-
native-a...](http://achipa.blogspot.com/2014/11/qml-wrappers-for-native-
android.html)). The good news is that you can still keep on the
JSON/Javascript side for all of this, regardless of whether you use custom
UIs, use Qt Quick Controls or something else.

Long story short - it's not quite an Appcelerator replacement just yet, but
certainly keep an eye on it! :)

------
adrianlmm
What's the difference between this and Xamarin?

~~~
achipa
This is a more full-stack approach - Qt and Xamarin are geared more towards
creating standalone apps. What you get here is the reactive back-end (plus
web-site for free). This setup can be used for both data and UI - you could
for example publish a new UI (not just content), and all native apps would
automatically be updated on the fly. If you take a look at the video - if you
do this with Xamarin (or Qt) you would need to manually connect to a database
or poll a RESTful service to see current data.

~~~
segphault
It's worth noting that if you wanted to create this kind of real-time app with
a Xamarin frontend, you could do it quite easily with ASP.NET on the backend
and SignalR.

~~~
achipa
That's certainly possible for the data part - but a lot harder for UI/code.
With the method I'm using, you can actually push code AND UI to the client on
the fly. As far as I know, that's a lot more difficult with Xamarin.

Also, the licensing is a lot more flexible than with Xamarin and Qt does
provide support for more platforms.

~~~
adrianlmm
It looks attractive, but at these times, the client application can be easily
be auto-updated, that's how all applications work, including those made by
Google.

~~~
achipa
Just wondering - what auto-update mechanisms are we talking about when it
comes to _native_ apps?

~~~
adrianlmm
In the case of Android, jsu uload the new version to Google Play and the
applicatio will auto-update it self.

~~~
achipa
This is not the same thing by a long shot - you cannot force a Google Play
update, and that update will take hours or days to trickle down to the users.
What we're talking about is that the application updates itself _instantly_ ,
even WHILE RUNNING. The user needs to nothing, no "update your app" or "newer
version available". I can literally add an option in the settings menu or
change something in the app and it will immediately be reflected on ALL
clients connected without touching the appstore.

------
Matthias247
If you want a higher-level cross-platform websocket layer between client and
server you could also checkout WAMP ([http://wamp.ws](http://wamp.ws)) as an
alternative to DDP. You would need to implement some things on your own, but
on the other hand it's more of an open standard and there are already multiple
targets available.

~~~
achipa
Looks nice - Meteor natively speaks DDP so it makes most sense to use when
talking to Meteor, but for other back-ends I will certainly consider WAMP! (no
reason why this principle could not be applied to other back-ends hooking into
the same WS powered Qt front-end)

