Author: tewari

Understanding and Using System.Transactions

These are some resources to help grasp System.Transactions functionality and use it effectively in your projects:

Features Provided by System.Transactions
http://msdn.microsoft.com/en-us/library/vstudio/ee818755(v=vs.100).aspx
Implementing an Implicit Transaction using Transaction Scope
http://msdn.microsoft.com/en-us/library/vstudio/ee818746(v=vs.100).aspx
MSDN Articles by John Papa
ADO.NET and System.Transactions
http://msdn.microsoft.com/en-us/magazine/cc163847.aspx
Revisiting System.Transactions
http://msdn.microsoft.com/en-us/magazine/cc163527.aspx
These are specific to TransactionScope (the way to go in most cases)
Here is a practical example of Using TransactionScope :
http://thewayofcode.wordpress.com/2011/12/11/handling-transactions-in-net-using-transactionscope/
This one gets in depth with the way a TransactionScope like functionality can be implemented. Gives you a good understanding of what is happening under the hood when using TransactionScope in some Repository implementations in multi-threaded scenarios.
http://msdn.microsoft.com/en-us/magazine/cc300805.aspx
Here is another example of implementing a transactional repository :
http://www.codeproject.com/Articles/31270/A-Transactional-Repository-Implementation-in-NET
There are excellent tips here about configuring TransactionScope when used with SQL Server:
http://blogs.msdn.com/b/dbrowne/archive/2010/06/03/using-new-transactionscope-considered-harmful.aspx
This is a good resource for CommitableTransaction usage – http://www.codeproject.com/Articles/55472/Committable-Transactions-in-C-SQL
And this one has brilliant under-the-hood coverage – http://www.codeproject.com/Articles/35087/Truly-Understanding-NET-Transactions-and-WCF-Impl

Protecting Your Api Keys

I am working on a Windows 8 app (details to follow in a subsequent post) and the code is published in a public repo on github. My app uses third-party APIs and after I committed the first cut to github, I realized that I had included my api keys in the code. The whole world had access to my keys. I did not want to publish the developer keys for those APIs to the entire world.

When the app will be released and distributed, those keys will need to be included in the app somehow. Once the keys are out there they can not be 100% protected from a determined mind. So, why bother? Why would I want to hide the api keys in the source code? Here are some good reasons –

1. It might be illegal to put the keys out there in plain sight for the whole world to see.
2. Developer keys may be throttled or have other restrictions on how many times they can be used per day or per minute.
3. The keys might allow access to expensive cloud computing resources.
4. The keys might allow access to confidential/sensitive customer data.

First, I had to take my keys back from git repo. Can you really remove information from a public git repository? Yes, you can, using git filter-branch. Here is how – https://help.github.com/articles/remove-sensitive-data. It worked! I successfully rewrote the history! My past commits don’t have those file(s) anymore that had my private api keys.

Next, I made sure that I don’t make this mistake again –

1. I added a new file ApiKeys.cs to the project.
2. Exposed the api keys as constants from a static class in this new file.
3 Added ApiKeys.cs in .gitignore file, to prevent this file from being committed to the repository.
4. Added instructions in ReadMe.txt for external developers to include their own keys.

This is not an ideal solution. If you are using a continuous build server, this technique will obviously not work. The code will not compile as-is, a file must be added to the project before it will start compiling. This works for me for now, but I am still looking for a better solution.

Solution to the fetch puzzle

Here is a brute force solution to the fetch problem –
Basically, at each step there are three possibilities :
1. You can fill a bucket.
2. You can transfer water from one bucket to the other one.
3. You can dump out the water from a bucket.
In this brute force solution, I try each one of these steps and then try all three again after each one of the previous steps. And on
and on untill I get the required amount of water in one of the buckets.
Check it out. Source code is on my github repo –
https://github.com/ashtewari/fetch

Here is a brute force solution to the fetch puzzle.

The puzzle goes like this – You have two buckets. A 3 gallon bucket and a 5 gallon bucket. Buckets are not marked or graduated. You are to fetch 4 gallons of water in a single trip to the river. How will you do it?

Basically, at each step there are three possibilities :

  1. You can fill a bucket.
  2. You can transfer water from one bucket to the other one.
  3. You can dump out the water from a bucket.

In this brute force solution, I try each one of these steps and then try all three again after each one of the previous steps. And on and on until I get the required amount of water in one of the buckets.

Check it out. Source code is on my github repo – https://github.com/ashtewari/fetch

Solve puzzle with code

Here is a quite common programming interview puzzle – You have two buckets. A 3 gallon bucket and a 5 gallon bucket. Buckets are not marked or graduated. You are to fetch 4 gallon of water in a single trip to the river. How will you do it?
Obviousy, this question is asked by changing the capacities of the two buckets and the amount of water to be fetched.
Your mission, should you choose to accept it, is to write a program to solve this puzzle in a generic way. Your program should take 3 inputs – capacities of the two buckets and the amount of water to be fetched. After solving the puzzle, your program must write out the solution step-by-step. You can use any programming language, any platform, any programming technique to write the program. Use whatever you like – C#, VB, C, C++, Java, Ruby, Python, F#, Boo, Javascript or any other language of your choice. Use design patterns, TDD, BDD, MVVM, Linq or whatever. Make it blazing fast, exploit multiple cores, use artificial intelligence. Go nuts! If you want to write the whole program in T-sql, powershell script or a batch script, go ahead. Heck ! you can even do it with regular expressions, if that your thing!
Your mission, should you choose to accept it, is to write a program to solve this common programming interview puzzle in a generic way.
The puzzle goes like this – You have two buckets. A 3 gallon bucket and a 5 gallon bucket. Buckets are not marked or graduated. You are to fetch 4 gallons of water in a single trip to the river. How will you do it?
tommylees-flickr-buckets
Photo Credit : http://www.flickr.com/photos/71256895@N00/3688461774/sizes/l/in/photostream/

Your program should take 3 inputs – capacities of the two buckets and the amount of water to be fetched. After solving the puzzle, your program must write out the solution step-by-step. You can use any language, any platform and any technique to write the program. Use whatever you like – C#, VB, C, C++, Java, Ruby, Python, F#, Boo, Javascript, powershell script or any other language of your choice. Use design patterns, TDD, BDD, MVVM, Linq or whatever. Make it blazing fast, exploit multiple cores, use artificial intelligence. Go nuts! If you want to write the whole program in T-sql, go ahead. Heck ! you can even do it with regular expressions, if that your thing!

Windigo 1.1 Released

windigo-samsungWindigo is a windows phone app to access your diigo account on windows phone 7.

Create, edit and search diigo bookmarks. Slick, to-the-point interface. Browse and search public bookmarks of other diigo users. Tap on the bookmark for details, including tags. Tap on any tag to narrow your search. Trial version is available.

Windigo 1.1 is out on the windows phone marketplace now.  Highlights of this update :

– Last SearchScope used is now persistent
– Fixed search when a search term is picked from suggested words
– Problem report now includes system info
– Handle crash on navigating from main page
– Fixed feature tracking for analytics
  • Last SearchScope used is now persistent
  • Fixed search when a search term is picked from suggested words
  • Problem report now includes system info
  • Handle crash on navigating from main page
  • Fixed feature tracking for analytics