Posts Tagged ‘Hibernate’

5 Tips for Building a Web SaaS

Sunday, February 15th, 2009

I have encountered tons of problems, some small, some large while building XP-Dev.com as a web software as a service (SaaS). To be honest, I was a little too naive and didn’t foresee some of these issues, and I really do hope it will help someone out there who’s thinking of building a SaaS for the masses.

1. Case Sensitivity

Case sensitivity of your unique keys is really important. For example, when you’re building a user database, you need to consider whether User1 is the same as uSeR1 and vice versa. Do note that email addresses are case in-sensitive and you’ll need to be able to cope with that in your application code. If you’re hosting your application on a Linux box, do remember that in general, Unix filesystems are case sensitive, and if you had a directory for User1 on your server, you could have another directory for uSeR1 as well.

On the database side, MySQL has a small bug nifty feature that will actually help you solve this headache a little. If you declare a column as a VARCHAR, searches on it are case insensitive, i.e. if you search for uSeR1, you will get back User1.

If you’re finding some weirdness around Hibernate, MySQL and case sensitivity, do have a look at by past blog about it.

2. Internationalization and Unicode

Just build everything on UTF-8, from the beginning, on each-and-every-file, on each-and-every-request. It will save you a whole load of headache later on when you’re considering releasing your SaaS to the non-english speaking world (and that’s a HUGE motha-** of a world that you don’t want to miss out on).

Use UTF-8 database tables. Depending on your installation, you’ll find that MySQL uses latin1, and that doesn’t bode too well with them accented and asian characters. The trick is to use the ‘CHARACTER SET‘ option when creating your database, and setting ‘charset=utf8‘ when creating tables.

Do use the awesome W3C HTML Validator to ensure that web browsers are reading your SaaS using the correct encoding:

3. Login/Register Lifecycle

Ahh yes, authentication! There’s a ton of research put into answering the question ‘How do I authenticate users on a website ?’. But my gripe is not about the authentication itself – it’s about doing the right thing after authentication.

Here’s a common scenario – User1 visits http://example.com/some/private/service/ which is an authenticated service – i.e. User1 needs to login to example.com to be able to access it. The problem is that some SaaS out there immediately redirect User1 to their ‘dashboard‘ or ‘homepage‘ on example.com – http://example.com/userhomepage.

This will frustrate users as they have to:

  • Remember the initial URL http://example.com/some/private/service/
  • Login
  • Retype http://example.com/some/private/service/ in the browser’s address bar
  • Press Enter.

The same applied if the user has not even registered for your SaaS.

The solution here seems pretty obvious – keep track of the last URL that a user hit before reaching your authentication pages, and upon successful registration or authentication, just redirect the user back to the original URL.

Most web frameworks will have support for this functionality in one form or another. Do look it up and get it in before the site goes live.

4. URLs and Permalinks

Keep everything in nice encapsulated URLs. This is a subjective area (that has been debated to an extent that it’s no longer funny), but I think having URLs that do not contain query paramaters are:

  • Easier to remember
  • Search engine/SEO friendly
  • Cleaner to regenerate in code

For example, instead of having:

http://example.com/some/private?service=login

You could instead have:

http://example.com/some/private/login

If you’re using a modern web server like Apache, Nginx or Lighttpd, they all provide some mechanism of rewriting URLs so you don’t have to modify your code too much.

5. Application Level Permissions Layers

Most SaaS are essentially database driven applications, and they all access the database under a single user. In some complicated setups, this can actually go to 2 users – one for reading and one for writing. An even more complicated setup, each user of the SaaS will have a database login.

All of these are essentially not enough.

And here’s why – in a world where a normalised database structure is all the hype, there’s a high degree of certainty that data for User1 sits on the same table as data for User2. As far as I know most databases don’t really have row level permissioning and hence, having to rely on your database as your permission layer just does not work.

There is one setup where I thought that it might work – give each user a new table or database. But clearly this is a solution that simply won’t scale.

So, what’s the alternative ? Embed it into your application code. The decorator or facade patterns are extremely powerful for implementing this. Moreover, you can do complex permissioning, for e.g. User1 can read the business object during weekends, but not when User2 is logged in at the same time. OK, fine – ts a bad example, but you get the point.

Why bother going through all this trouble ? Well, here’s a generic use case:

MyCalendar app is a web SaaS online calendar offering. Each user can have multiple calendars, and they are all private to the user. To retrieve a calendar, all a user has to do is visit http://example.com/calendar/<calendar id>/ where calendar id is an identifier on a database table.

Say User1 has calendars with calendar ids 240, 252 and 362. If MyCalendar app didn’t have application level permissioning, User2 would happily be able to view all 3 of User1’s calendar.

So, the natural question to ask is “Do users actually try to do that ?”. YES! They will. I’m not sure whether they are curious, or looking for a security hole, but you will find some users exploring the URLs. What I mean by that is, say User2 has a calendar id of 5442. He/She will try to visit the URLs for calendar id 5440-5449, even though there are no direct links to those calendars that they can see (except 5442).

Using a database driven web framework like Rails and Django is all well and good, but remember to implement some application level permissioning if you have any private data.

There You Have It

5 simple tips that will save you a ton of hassle if you’re building an SaaS. As always, feedback is appreciated.

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Hibernate, MySQL and Case-Sensitivity

Wednesday, October 29th, 2008

Since going live with XP-Dev.com a few months ago, there has been a nasty little bug that I’ve been trying to chase down where a weird exception is thrown in some obscure situations. When I say “weird”, I mean “I look at the code and keep saying to myself: this exception can’t possibly be thrown here”. Now, the exception is very domain specific and its almost pointless for me to attempt describing it here, as that will take a few posts, rather than just the one.

In a nutshell, a user could login to XP-Dev.com using valid username and password credentials, but then found that he/she could not perform any tasks. It turns out that this only happens if a user logs in using a slightly different case for his/her username. For e.g. When user ‘developer‘ logs in using ‘Developer‘, he’ll basically hit this bug.

The problem is two fold:

First, MySQL stores varchar columns as case insensitive. So, when you run a SQL query like:

select * from Users where username='Developer'

MySQL will return the rows with username ‘developer’.

This is not a problem per-se, as I’ve found this design feature pretty useful when attempting to do web oriented work in the past. The web in general is case insensitive, and system facing the web should reflect that. There is no difference between XP-Dev.com and xp-dev.com.

So, from this perspective, its not really a security bug as well, as you can’t really register the user ‘Developer’ anyway and attemp to ’steal’ the other user.

Here comes the annoying second part of this fiasco.

I use Hibernate as a Object Relationship Mapper/Persistence Layer on the current version of XP-Dev.com. Carrying on with the MySQL example above, pulling out a User object from the Users table using Hibernate can be done as follows:

User user = (User) org.hibernate.Session.get(User.class,
                                             "Developer")

The problem is that the User object returned will have the member ‘username’ set to ‘Developer’, rather than ‘developer’ as it is on the database. The object that Hibernate returns to you does not reflect the database state at all.

Coming back to the bug: Whenever a user logs in, I keep his username in memory attached to his session on the server-side, and refetch a fresh new User object on every HTTP request. The problem was that performing any tasks failed because it relied on strong Foreign Keys on the database tables. For e.g. if user ‘developer’ had 3 repositories, and logs in using ‘Developer’, I will refetch ‘Developer’ using Hibernate and get the username ‘Developer’ back, rather than ‘developer’. The user ‘Developer’ does not have any repositories and the permissions layer that I wrote (which is case sensitive) will throw a nasty exception when user ‘Developer’ tries to access repositories for the user ‘developer’. The permissions layer should be case sensitive as it’s a very critical part of the architecture and should be as restrictive as possible.

It’s nasty the way Hibernate does not return the exactly values back on the data object as it is on the database. The work-around is to use something like below:

org.hibernate.Session.createQuery("from User where username = ?")
                             .setParameter(0, "Developer")
                             .list()

Magically, Hibernate DOES return a User object with username set to ‘developer’. This approach has an extra overhead of creating a list on every call, but I suppose I’ll have to live with that for now.

On the new version of XP-Dev.com, I got rid of Hibernate and Wicket. I’ve had growing pains with Wicket as well, but that’s a rant for another blog post. Hibernate is just too bloated, and I can’t afford the performance overhead.

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