Feedback on using Google App Engine?

Note that currently, you can't get F# in an Express edition, though I imagine that this is likely to change at some point in time.

Take a look the the sql game, it is very stable and actually pushed traffic limits at one point so that it was getting throttled by Google. I have seen nothing but good news about App Engine, other than hosting you app on servers someone else controls completely.

The "App Engine running Django" idea is a bit misleading. App Engine replaces the entire Django model layer so be prepared to spend some time getting acclimated with App Engine's datastore which requires a different way of modeling and thinking about data.

Edit: Models should be specially designed considering all the transactions you wish to have in future, because entities only in same entity group can be used in a transaction and it makes the process of updating two different groups a nightmare e.g. transfer money from user1 to user2 in transaction is impossible unless they are in same entity group, but making them same entity group may not be best for frequent update purposes.... read this http://blog.notdot.net/2009/9/Distributed-Transactions-on-App-Engine

I was just getting into the datastore portion of the project when I got pulled away for "real work".

I was able to accomplish a lot (it still is not done yet) in a very little amount of time. Since I had never used Python before, this was particularly pleasant (both because it was a new language for me, and also because the development was still fast despite the new language). I ran into very little that led me to believe that I wouldn't be able to accomplish my task. Instead I have a fairly positive impression of the functionality and features.

That is my experience with it. Perhaps it doesn't represent more than an unfinished toy project, but it does represent an informed trial of the platform, and I hope that helps.

I used GAE to build http://www.muspy.com

Assuming that your objects are all of a similar type you could add a method as a category of their base class that calls the function you're using for your criteria. Then create an NSPredicate object that refers to that method.

It's a bit more than a toy project but not overly complex either. I still depend on a few issues to be addressed by Google, but overall developing the website was an enjoyable experience.

If you don't want to deal with hosting issues, server administration, etc, I can definitely recommend it. Especially if you already know Python and Django.

If you are OS X 10.6/iOS 4.0 or later, you're probably better off with blocks than NSPredicate. See -[NSArray indexesOfObjectsPassingTest:] or write your own category to add a handy -select: or -filter: method (example).

I am using GAE to host several high-traffic applications. Like on the order of 50-100 req/sec. It is great, I can't recommend it enough.

My previous experience with web development was with Ruby (Rails/Merb). Learning Python was easy. I didn't mess with Django or Pylons or any other framework, just started from the GAE examples and built what I needed out of the basic webapp libraries that are provided.

If you're used to the flexibility of SQL the datastore can take some getting used to. Nothing too traumatic! The biggest adjustment is moving away from JOINs. You have to shed the idea that normalizing is crucial.

Ben

I used GAE and Django to build a Facebook application. I used http://code.google.com/p/app-engine-patch as my starting point as it has Django 1.1 support. I didn't try to use any of the manage.py commands because I assumed they wouldn't work, but I didn't even look into it. The application had three models and also used pyfacebook, but that was the extent of the complexity. I'm in the process of building a much more complicated application which I'm starting to blog about on http://brianyamabe.com.

I used GAE to build a simple application which accepts some parameters, formats and send email. It was extremely simple and fast. I also made some performance benchmarks on the GAE datastore and memcache services (http://dbaspects.blogspot.com/2010/01/memcache-vs-datastore-on-google-app.html ). It is not that fast. My opinion is that GAE is serious platform which enforce certain methodology. I think it will evolve to the truly scalable platform, where bad practices simply not allowed.

I used GAE for my flash gaming site, Bearded Games. GAE is a great platform. I used Django templates which are so much easier than the old days of PHP. It comes with a great admin panel, and gives you really good logs. The datastore is different than a database like MySQL, but it's much easier to work with. Building the site was easy and straightforward and they have lots of helpful advice on the site.

NSPredicate is nextstep's way of constructing condition to filter a collection (NSArray, NSSet, NSDictionary).

For example consider two arrays arr and filteredarr:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF contains[c] %@",@"c"];


filteredarr = [NSMutableArray arrayWithArray:[arr filteredArrayUsingPredicate:predicate]];

to make it easy to remember those who little sql background it is

*--select * from tbl where column1 like '%a%'--*

the filteredarr will surely have the items that contains the character c alone.

1)select * from tbl --> collection

to make it easy to remember those who little sql background it is

*--select * from tbl where column1 like '%a%'--*

2)column1 like '%a%' --> NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF contains[c] %@",@"c"];

1)select * from tbl --> collection

3)select * from tbl where column1 like '%a%' -->

[NSMutableArray arrayWithArray:[arr filteredArrayUsingPredicate:predicate]];

I hope this helps

2)column1 like '%a%' --> NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF contains[c] %@",@"c"];

This question has been fully answered. Which is good. But one thing perhaps is worth mentioning. The google app engine has a plugin for the eclipse ide which is a joy to work with.

If you already do your development with eclipse you are going to be so happy about that.

To deploy on the google app engine's web site all I need to do is click one little button - with the airplane logo - super.