Presenting at the conference

Yesterday there was an in-house tech conference at stratton finance and was a part of it. Moreover - that was my first experience at presenting something in Australia!
First thing first - I really enjoyed it. And I`ve leaned a lot from the presentation itself and from preparation to it.

My topic was 'Docker containers'. I haven't used docker before so first thing I did was just a fresh installation of the docker to my Ubuntu laptop. Somehow I failed to install using official tutorial - so had to install it differently :) And when all was done I was able to pull few containers and run them - great success! Maybe, soon I`ll start using it mush more and not only locally...

We are at stratton not using docker at the moment so my presentation was a kind of 'what we can use'. Others were more about what are we using at the moment/what we will be using next week. I am not sure if this was good or not, should the theme of the conference be more focused?

Probably, the most important lesson I've learn was the obvious one - you need to prepare your speech. I was lazy and combined the presentation only the night before the event. My speech was not prepared at all - just few bullet points, almost duplicating the presentation. Surprisingly that was almost enough - I just forgot the name 'Core CLR' I wanted to use and it was an awkward pause. But other then that I hope my talk was smooth and interesting. Heh, I should ask for a feedback tomorrow!

As I said, I really enjoyed it and if the feedback would be positive enough I am going to start presenting at local meetups!

Nullable comparisons simplified with LINQ

What if you need to compare few nullable values? For example, you store latest call date and latest email date and need to define the latest contact date - either call or email. The simplest approach in that case probably is

DateTime? callDate, emailDate;

var latestDate = callDate ?? emailDate;
if (callDate.HasValue && emailDate.HasValue)
    latestDate = callDate > emailDate
                ? callDate
                : emailDate;

Simple and straightforward. Especially if you have read Eric Lippert`s blog post about nullable comparisons. But what if you have third option - liveConversationDate? Or something even bigger? Writing all those conditions one by one can be troublesome.
I found that LINQ is the simplest approach. Just combine all values into a list, filter out nulls (or apply your business rules) and order it!

 int? a, b, c;
 a = null;
 b = 5;
 c = 3;
 
 var res = new List<int>() {a, b, c};
 Console.WriteLine(res.OrderByDescending(i => i).First());
 Console.WriteLine(res.OrderBy(i => i).First());
 Console.WriteLine(res.Where(i => i != null).OrderBy(i => i).First());

How to compare approximate dates with SQL

Let say you have to write a code for the periodic payment application, and in your database you store the payment start date. After that you want to check if the next payment is within +/- 1 day of the current date - do something. And obviously, you font want to write a lot of code to do that :)

The first idea I had was to create a whole bunch of unions for each day and then check if current date is one of those, but later I shrinked that to 3 conditions connected with 'or' (here is NHibernate function for that)

var settlementDateDifferenceFromNow = Projections.SqlFunction(
 new SQLFunctionTemplate(
  NHibernateUtil.Int32,
  @"
  CASE WHEN
  ABS(DATEDIFF(DAY, GETDATE(), DATEADD(MONTH, DATEDIFF(MONTH, ?1, GETDATE()) - 1, ?1))) <= 1 OR
  ABS(DATEDIFF(DAY, GETDATE(), DATEADD(MONTH, DATEDIFF(MONTH, ?1, GETDATE()), ?1))) <= 1 OR
  ABS(DATEDIFF(DAY, GETDATE(), DATEADD(MONTH, DATEDIFF(MONTH, ?1, GETDATE()) + 1, ?1))) <= 1
  THEN 1
  ELSE 0
  END
  "),
 NHibernateUtil.Int32,
 Projections.Property<Contract>(x => x.SettlementDate_Actual)
);

I am not sure about 'or' conjunction tho... would it cause performance problems?

Nhibernate paging for time consuming operations

Imagine, you have to implement batching for a time consuming operation using NHibernate. I would write it like this:

var items = new List<Item>();
for (var page = 0; page == 0 || items.Any(); page++)
{
    items = GetListOfItems(page);
    foreach (var items in items)

    {
        DoStuff(item);
    }
}

public void GetListOfItems(int page)
{
    return CurrentSession.QueryOver<Item>()
        .Select(Projections.Id())
        .Take(PageSize)
        .Skip(PageSize * page)
        .List();
}

But what I found is that if the DuStuff is time consuming then it is possible to have duplicated items from the query. Thatis because of NHibernate generated query:

SELECT TOP (@p0) y0_
FROM (
  SELECT this_.Id AS y0_
  ,ROW_NUMBER() OVER (
    ORDER BY CURRENT_TIMESTAMP
  ) AS __hibernate_sort_row
  FROM contact.sfContact this_
) AS query
WHERE query.__hibernate_sort_row > @p1
ORDER BY query.__hibernate_sort_row;

That order by CURRENT_TIMESTAMP... If you want consistent results you would have to apply specific ordering:

public void GetListOfItems(int page)
{
    return CurrentSession.QueryOver<Item>()
        .Select(Projections.Id())
        .OrderBy(i => i.Id).Asc
        .Take(PageSize)
        .Skip(PageSize * page)
        .List();
}

How to fail an interview (or learn from others mistakes)

I think of myself as "open for opportunities" professional. I have a great job that I like but I dont mind to try something new. Recently I found a really interesting puzzle - part of the employment process. That was a task to recreate a web service by its interface so the checking bot could access it and try its tests.

Sounds fun so I decided to try. The hardest part of that process was to understand what is the expected behavior of that service just by methods names. And take into account all tricks from the employer side (like overflow exceptions, impossible combinations of parameters etc.) I`ve solved that puzzle to 90% and that was enough to pass to the real interview. At that  point I`ve decided to try the interview as well - just in case :). Unfortunately, I failed and here is my thoughts about the interview.

That was completely my mistake. I have not really prepared myself to the interview and have not refreshed in my memory the most common questions. I thought that I dont need anything to pass.
Here is the list of some of those questions from the interview with my comments - maybe it would help someone (and all of them about c#).

• Difference between value type and reference type 
• hopefully everyone can explain it from the top of their heads).
• Boxing vs Unboxing ()
• I`ve made my first mistake here as I could not remember what is what...
• Is string a value type or reference type?
• Just be careful here as well as string is a special case. I`ve remembered it but not sure what I`ve answered :)
• What is sealed keyword? Can we derive from sealed class?
• some questions about garbage collector
• Cant remember those questions, they were like when collector does its work by default, how to suspend it etc. I dont know a lot about it as that's not a day-to-day stuff. Possibly mine knowledge of GC.Collect and that that is not a best line of code to include just not enough :)

• SOLID principles
• simply name them
• Describe Strategy pattern; Singleton pattern
• once again, describe them in your own words
• What are 4 types of design patterns
• I could not remember them, but the common sense is your friend - some of them are aimed at creation of objects, other about interactions and so on.

• Session variables in Asp.Net
• that was a question about ViewBag, ViewData and TempData. I could not remember them (and the difference between them) as I just so get used to models. Unfortunately, I have not described my thoughts on Models either - so that is my big mistake...
• Authorization in Asp.Net
• I started talking about security tokens and roles, but the question was only about [Authorize(Roles = "...")] attribute. And I forgot to mention it :(
• Can 2 different routes lead to the same action in Asp.Net?
• Yes - but it would be better to answer with example and I just said yes.
• Difference between Shared views and Partial Views
• Own words explanation
• Difference between WebForms and MVC
• I`ve told about postbacks and stateless MVC controllers, probably that was not what interviewer was expecting...
• Is doctype needed for HTML5?
• I`ve said that no (from the personal experience) but accordingly to the documentation - the answer is yes...

• What is the difference between Data Contract and Operational Contract in WCF
• I`ve answered honestly that I dont really know WCF :( And by the way, in the job ad there was no mention of WCF
• Can WebAPI method return ActionResult?
• I`ve answered that yes (especially as I can wrap it as I want) but the proper answer was no
• Can WebAPI replace WCF
• Em... Yes?

• Are dependencies in IoC framework singletons?
• They can be, for example:NInject
• Lifetime management of dependencies in IoC framework

• What will I do and how would I approach bug fixing at some client as a software development consultant?
• How can I monitor problems in production?
• What is TDD, BDD, DDD, Kanban?

After about hour of talking on those questions I was given a small tax calculator application with bugs and txt file with tests. My task was to fix as many bugs as possible and the interviewer was looking at my screen with Skype shared desktop. I`ve fixed some of those tests (not all of them) and after another 30 minutes interviewer asked me to show only the first test - and that was all.

And finally, on the next day or so I`ve received the email with "sorry you failed.". Not a big deal :)

Now I can learn from mine mistakes :)

Shortening url using google api

Today I edited a question on stackoverflow about url shortening. Looks like it was about Json serialization, and here is my solution:

 using (var client = new HttpClient())
 {
  var content = new StringContent(
   "{\"longUrl\": \"http://www.google.com/\"}",
   Encoding.UTF8,
   "application/json");

  var response = await client.PostAsync("https://www.googleapis.com/urlshortener/v1/url", content);

  var responseString = await response.Content.ReadAsStringAsync();

  var data = JsonConvert.DeserializeObject(responseString);

  var id = data.Id;
 }

And a class for urls:

 public class ShortenUrl
 {
  public string Kind { get; set; }

  public string Id { get; set; }

  public string LongUrl { get; set; }
 }

So you would have to use Newtonsoft json serializer to deserialize the json string; and HttpClient to communicate with the API

YOW 2014

Thanks to my company, stratton, I was able to attend the YOW! conference in Melbourne. It was a 2-day software conference and it was amazing :). I really liked everything, especially as it was my first big conference.
For now I want to leave some notes about sessions I visited.

Day 1:

1) User story mapping: Discover the whole story by Jeff Patton. It was good especially as Jeff is a great presenter. But the content was a little bit childish - too easy and nothing special.
2) Make impacts, not software by Gojko Adzic. Second session was not very deep as well and I suppose nobody would expect to get some out-of-the box solutions; so from that session I was able to get few ideas at least like how to piss of scrum masters :) Or why we don't actually need all that test coverage.
3) Cool things about D - why and how we use it at Facebook by Andrei Alexandrescu. Finally that was a great speech. Andrei not only covered the simple usage of D (in a great way! so I started to plan when I will download its compiler) but as well talked about purity and some general programming concepts. It was useful and interesting. I would say that it was one of the best sessions from today.
4) Groovy: the awesome parts by Paul King. I wanted to get into groovy a little and the session started with an idea that groovy is the same thing for java as D for C++ but, unfortunately, this topic was not of the same quality as previous one. Frankly, it was just boring... Basic examples and no real value. At least for me.
5) Programming in the large: Architecture and experimentation by Mark Hibberd. Mark did a great job of general description of the general programming myths with a real examples of what his team doing. He even admitted that they could do it better! It was fun to listen to him and it was really motivational. Once again - it made me think of what and how I would do in the future. Thank you Mark.
6) Functionally obvious and succinct by Edward Kmett. This session was hard. Really hard. First of all - I had never seen haskel code before and secondly - it was all about optimization so a lot of "o(log(n))". And during the session I almost constantly had a question "wat" in my head. But later on the way home I rethought what I heard and it comes that this topic is interesting for me and I would like to try to implement the same data structure with C# (and will post about it soon).

Day 2:

1) Reactive, message driven and scalable by Todd L. Montgomery. Todd was talking about the past, present and future of the http protocol. Interesting topic but it was pretty much summarized by his own words that it is likely that most deevlopers wont notice any difference - it is too low level.
2) The scaling dilemma by Mary Poppendieck. Another session about the "agile way". This time on how to scale the agile approach for the enterprise level. Frankly, just another agile talk - nothing new. Maybe those agile coaches just aiming for a real general things?
3) How we went from 1 million to 1 billion events without throwing everything away by Julian Giuca. That was just boring - Julian was speaking about their approach to frameworks, made a lot of examples and he is a good speaker. But the topic was just bad, nothing specific and nothing useful - just a bunch of general ideas that everyone can produce.
4) How to undo almost anything with Git by Peter Bell. Finally, that was the only session on that conference (for me) where the speaker was not only showing slides but actually type something. During that speech I was enjoying the real console and actual usage of the Git. That was really fun!
5) Agility at the essence of software architecture by Simon Brown. Luckily, that session was not a common agile talk. From that one I was able to catch some new ideas and approaches, I am very pleased that I have seen it. Sketching is great :)
6) Pippi's book of the dead trading cards by Elizabethe Kramer. Well, the last session of the conference was the worst one. It was more about psychology then development and it was really bad. Elizabeth told us how she was able to settle one unpleasant situation  for one company. But why I would like to know it - I don't know :)

So that was all. Unfortunately, I was not able to network at all, my social skills need a lot of improvements!