VB.NET’s DateTime anatomy represents an burning in time and is usually bidding as a accurate date and time of the day. DateTime comes in accessible whenever you charge to actuate the system’s date and time; it aswell performs assorted operations on date/time variables. In this article, I appearance how to advance DateTime backdrop and methods so you can plan with DateTime ethics in VB.NET.

Here are listings of the a lot of frequently acclimated backdrop and methods of the DateTime structure.

Properties:

1. Date: allotment the date basic of the DateTime value.
2. Day: allotment the day of the ages basic of the DateTime value.
3. DayOfWeek: allotment the day of the anniversary basic of the DateTime value.
4. DayOfYear: allotment the day of the year basic of the DateTime value.
5. Hour: allotment the hour basic of the DateTime value.
6. Millisecond: allotment the milliseconds basic of the DateTime value.
7. Minute: allotment the minute basic of the DateTime value.
8. Month: allotment the ages basic of the DateTime value.
9. Now: allotment a DateTime amount that is the accepted bounded date and time on this computer.
10. Second: allotment the abnormal basic of the DateTime value.
11. TimeOfDay: allotment the time of day of the DateTime value.
12. Today: allotment the accepted arrangement date.
13. UtcNow: allotment a DateTime amount that is the accepted bounded date and time on this computer bidding as the Coordinated Universal Time (UTC).
14. Year: allotment the year basic of the DateTime value.

Methods :

1. Add: adds the amount of the defined TimeSpan to the DateTime value.
2. AddDays: adds the defined amount of canicule to the DateTime value.
3. AddHours: adds the defined amount of hours to the DateTime value.
4. AddMilliseconds: adds the defined amount of milliseconds to the DateTime value.
5. AddMinutes: adds the defined amount of account to the DateTime value.
6. AddMonths: adds the defined amount of months to the DateTime value.
7. AddSeconds: adds the defined amount of abnormal to the DateTime value.
8. AddYears: adds the defined amount of years to the DateTime value.
9. DaysInMonth: allotment the amount of canicule in the defined ages of the defined year.
10. IsLeapYear: allotment an adumbration of whether the defined year is a bound year.
11. Subtract: subtracts the defined time or continuance from the DateTime value.
12. ToLocalTime: converts the accepted Coordinated Universal Time (UTC) to bounded time.
13. ToLongDateString: converts the amount of this instance to its agnate continued date cord representation.
14. ToLongTimeString: converts the amount of this instance to its agnate continued time cord representation.
15. ToShortDateString: converts the amount of this instance to its agnate abbreviate date cord representation.
16. ToShortTimeString: converts the amount of this instance to its agnate abbreviate time cord representation.
17. ToUniversalTime: converts the accepted bounded time to Coordinated Universal Time (UTC).

One of the thngs I like about my job is solving problems. In particular problems where there is a bit of thought involved. The particular problem I had is that for a search interface I’m building a requirement is the ability to page result set. This is easy using MySQL as it has a LIMIT keyword that limits the results to a certain number, and allows an offset, so for example you to retrieve results 16-20 you would use LIMIT 15,5.

Unfortunately, SQL Server does not have an equivalent to the offset argument. Its nearest is TOP n, which returns the first n rows.

This puzzled me for a few days, but then the answer came to me in a flash of inspiration: Results 20-16 would be the first 5 rows of a TOP 5 statement, with a nested query with a TOP 20 statement in the opposite order. Then I could just reverse the order to get the result the right way around.

So here’s what I came up with:

SELECT * FROM (
	SELECT TOP x * FROM (
		SELECT TOP y fields
		FROM table
		WHERE conditions
		ORDER BY table.field  ASC) as foo
	ORDER by field DESC) as bar
ORDER by field ASC

x is the number of rows you want returned and y is x+offset.

After looking at this in Query Analyzer, it appears that the extra nesting does not add very much to the load. For the queries I was running it was only about 2%.

Source: http://josephlindsay.com/archives/2005/05/27/paging-results-in-ms-sql-server/

I discovered a very interesting little twist on the differences between the Today property and the Now property in the DateTime Class. I was working on something recently and using the built-in Compare method of the DateTime Type. Essentially the user selected a date and I had a validation snippet that was supposed to check that they had not picked a future date. One of the ways they could choose their date was via a DateTimePicker control. I thought that this code might do the trick:

Dim EndDate As DateTime
Dim Current As DateTime = Today

If DateTime.Compare(Current, EndDate) < 0 then
    label6.text ="" "CONTRACT EXPIRED LESS THAN"
end if
if datetime.compare(current, enddate) ="" 0 then
    label6.text ="" "CONTRACT EXPIRED EQUALS"
end if
if datetime.compare(current, enddate) > 0 Then
    Label6.Text = "CONTRACT NOT EXPIRED GREATER"
End If

Dengan support terbaru yang terdapat pada .NET, beberapa fitur telah ditambahkan. Salah satunya adalah “Build Typesafe Generic Classes“. Sekarang kita dapat menyelesaikan permasalahan pada type data NULL.

Apakah biasanya anda melakukan pelambangan pada data yang NULL? Saat ini .NET telah melakukan perbaikan dan solve problem.

Nilai NULL yang dikenali oleh Visual Basic sebagai flag istimewa yang menunjukkan data yang tidak muncul. kebanyakan nilai NULL menunjukan bahwa resource atau bisa kita ibaratkan benda tersebut ada tetapi tidak terlihat atau tidak terciptakan. Misalnya pada kode berikut, FileStream berisi Null referensi karena tidak ter-instantiated dengan New Keywords:

Dim fs As FileStream
If fs Is Nothing
    Console.WriteLine("Object contains a null reference.")
End If

Core tipe data seperti  integer dan string tidak dapat berisi NULL Values. Variable numerik akan otomatis bernilaoi 0 (Nol) dan boolean akan berisi variable False. Sedangkan tipe data String akan berisi kosong (“”) secara otomatis. Pada dasarnya, bila anda melakukan set type data dengan variable Nothing pada code, akan secara otomatis bila terjadi kekosongan data akan dikembalikan pada nilai kosong (0,False,””). Contoh:

Dim j As Integer = Nothing
If j = 0 Then
    Console.WriteLine("Non-nullable integer j = " & j)
End If

Bentuk ini kadang-kadang menyebabkan masalah, dimana tidak ada pembeda antara nilai kosong (NULL) dengan nilai yang tidak pernah ada. Secara sederhana saya contohkan, bila anda membuat code dimana anda harus mengembalikan nilai text pada textbox dan pada saat itu diset 0, maka anda tidak dapat tahu, apakah textbox tersebut memang kosong atau 0 adalah nilai awal (Tentu saja bila tidak disertai Flag-flag tertentu sebagai konfigurasi).

.NET 2.0 telah memberikan solusinya, yaitu System.Nullable Class yang dapat melingkupi berbagai macam tipe data. Bila anda membuat suatu definisi yang tidak mempunyai nilai awal (atau nullable) atau tidak melakukan setting nilai dasar, maka anda dapat melakukan test dengan metode Nullable.Hastype() dan anda akan mendapatkan nilai balik Nullable.Value

Berikut contohnya:

Dim i As Nullable(Of Integer)
If Not i.HasValue Then
    Console.WriteLine("i is a null value")
End If

i = 100
If i.HasValue Then
    Console.WriteLine("Nullable integer i = " & i.Value)
End If

…Memakai Nullable sebagai referensi object sangat bermanfaat walaupun anda tidak membutuhkannya, ini akan tetap dapat memberikan anda keuntungan, yaitu paling tidak kode anda akan lebih mudah untuk dibaca HasValue() yaitu metode yang lebih baik untuk melakukan tes untuk value Nothing. Yang terbaik adalah, anda dapat mengadakan perubahan secara berkesinambungan, karena Class Nullable mempunyai kemampuan untuk melakukan konversi antara Nullable dengan type data itu sendiri.

If sometime you wite code in VB and you will find data into database that’s empty (read Null) and that’s maybe a big problem. Why you not insert some character to make the data field in data row sorted not null…? maybe you have some reason that make it cannot applicated into data storage. You can try solution with ISNULL() Function.

Syntax:
IsNull(expression)

Return Data type:
Boolean

Example:

If IsNull(RsData!telp_asal) = True Then
      Text1(4).Text = ""
      Text1(5).Text = ""
Else
      Text1(4).Text = Mid(RsData!telp_asal, 1, InStr(RsData!telp_asal, "-") - 1)
      Text1(5).Text = Mid(RsData!telp_asal, 1, InStr(RsData!telp_asal, "-") + 1)
End If

That’s it…. simple methode to handle null data from database.

I you your Ubuntu Box upgraded to hardy and rebooted. When you log in to Gnome, a Nautilus window flashes up and quickly disappears about ten times. There are no icons on the desktop. When I try to start Nautilus from the terminal and you may get:

Initializing gnome-mount extension
seahorse nautilus module initialized
nautilus: symbol lookup error: /usr/lib/

nautilus/extensions-1.0/libgnome-mount.so: undefined symbol: nautilus_file_info_get_drive

So… you maybe cry :p

It’s okay, you can do this step to resolve your problem:

1. sudo apt-get autoremove nautilus
2. sudo apt-get install nautilus

Yes… that’s it… and problem solve!!!

If you use the InnoDB storage engine for (some of) your MySQL tables, you’ve probably already came across a problem with its default configuration. As you may have noticed in your MySQL’s data directory lies a file called ‘innodb1?. It holds almost all the InnoDB data of the MySQL instance and could get quite big. Unfortunately, by design InnoDB data files can’t be shrinked. That’s why DELETEs, TRUNCATEs, DROPs, etc. can’t will not reclaim the space used by the file. Instead any freed regions are marked as unused and can be used later. Theoretically speaking the file could reach the maximum size allowed by the filesystem if no limit is set in the my.cnf file. Guess what ? It’s not set by default. However you can configure your InnoDB engine as described MySQL’s Reference Manual. Additionally you can force the server to create an *.ibd for each newly created InnoDB table by using the ‘innodb_file_per_table‘ option.

As mentioned above, you cannot shrink InnoDB data files. Additionally, you cannot make much changes in the settings of a InnoDB data file. So if you haven’t configured InnoDB properly right after the installation, you’ll probably have a pretty large ibdata1 file. There are three ways to reclaim your free space, but before doing so backup your whole MySQL data directory… just in case. And don’t forget to stop any services using MySQL databases.

Dump the Whole Database

In fact, this is the method I used to solve the problem. It requires much more space and time but it’s maybe the easiest one. So here it is:

1. Dump all databases by calling:
   

   /usr/bin/mysqldump –-extended-insert –-all-databases –-add-drop-database –-disable-keys –-flush-privileges –-quick –-routines -triggers > all-databases.sql

2. Stop the MySQL server;
3. Rename or remove (in case you’ve already backed it up) the MySQL data directory and create an empty one with the same name and permissions;
4. Make the appropriated changed in my.cnf;
5. From the command prompt issue ‘mysql_install_db‘ in order to re-initialize the database;
6. Start the MySQL server;
7. Get into the ‘mysql‘ console and type:
   

   SET FOREIGN_KEY_CHECKS=0;
   SOURCE all-databases.sql;
   SET FOREIGN_KEY_CHECKS=1;

:) Have fun !