Tag Archives: Microsoft

When SqlDataReader is missing rows

I have a very basic scenario:

  1. Execute TSQL Stored procedure
  2. Return a DataReader
  3. Read data from the Reader

This is ADO.NET 101. There is one problem: DataReader loses rows. This problem has haunted me forever, extensive research and numerous suggestion didn’t help, even though the code is extremely basic:

Get the reader:

m_dbSel.CommandType = CommandType.StoredProcedure
m_dbSel.CommandText = "SP_Name"
oResult = m_dbSel.ExecuteReader()

Pass the reader to class constructor to fill Generic List (of Integer): 

Public Sub New(i_oDataReader As Data.SqlClient.SqlDataReader)

    m_aFullIDList = New Generic.List(Of Integer)

    While i_oDataReader.Read
        m_aFullIDList.Add(i_oDataReader.GetInt32(0))
    End While

    m_iTotalNumberOfRecords = m_aFullIDList.Count

End Sub

This problem occurs when number of rows returned by the reader is relatively large (over 600,000 records). If this happens – number of rows added to the list from the reader is inconsistent, but always less than real one. Most often “magic” number of 524289 rows is returned.

Well, this is no longer a mystery, thanks to the great people from Stack Overflow @RBarryYoung, @granadaCoder and especially @MartinSmith who was the first to point me in the right direction – and here it is.

Even though the problem is with SqlDataReader – it is happening because it is used in conjunction with Generic List. List, as you may know has a flexible Capacity for number of elements it can store. When count of elements exceeds capacity – capacity increases and always to a power of 2. E.g.

When the count exceeds 4 elements – capacity is set to 8 (2^3)
When the count exceeds 8 elements – capacity is set to 16 (2^4)
When the count exceeds 16 elements – capacity is set to 32 (2^5)

etc..

This is what makes Generic List such a powerful tool, used by many large scale .NET projects, e.g. bingogodz.com. And ordinary this is not a problem. Unfortunately this is not the case when it is used together with SqlDataReader. When count of items in the List exceeds 524,288 (2^19) and its capacity is set to 1,048,576 (2^20) – SqlDataReader’s Read method suddenly returns False even though not all records have been read. No exception is thrown, it simple stops.

The only possible workaround I’ve found so far (I am still looking for better ones) is to pre-set List capacity in advance. Since, when using DataReader, you do not know number of rows, you’re left either with hardcoding the number or running another DB query to retrieve number of rows via something like COUNT(*). Like I said, I don’t like this workaround, please let me know if you find a better one.

UPDATE: Finally figured it out: http://stackoverflow.com/a/18520609/961695

Access your PC files remotely via SkyDrive on mobile device

If you use Microsoft Skydrive application on your Windows machine, you know that besides syncing local dedicated Skydrive folder to the cloud it allows accessing your PC files directly (without uploading them to the cloud) from remote location. Unfortunately this feature is available for desktops only, mobile apps are “by design” missing it.

But what prevents you from logging into Skydrive Website directly from a mobile Web browser?

Skydrive In Mobile Chrome

After authorizing yourself with security code you’re in! Albeit this is not as convenient as a native app would be, but until “design” changes this approach allows you to access your PC’s files without installing any additional software on the PC and without downloading any additional app to the device.

Solution for: Value of type ‘System.Web.UI.HtmlControls.HtmlGenericControl’ cannot be converted to ‘System.Web.UI.HtmlControls.HtmlTableRow’ error

If you’re trying to compile an ASP.NET project/website in Visual studio 2012 or 2010 and getting error:

Value of type ‘System.Web.UI.HtmlControls.HtmlGenericControl’ cannot be converted to ‘System.Web.UI.HtmlControls.HtmlTableRow’

chances are you have an HTML table in your ASPX markup with runat="server" attribute set and <tbody> or <thead> tags present. Remove <tbody> and <thead> tags and the error should go away.

Sync NEW files from external folders to Skydrive

Skydrive
If you use Microsoft Skydrive cloud storage, you know it has a neat desktop client that automatically syncs content of a desktop folder to the cloud. It uses its own dedicated folder, but if you have existing folders that accumulated photos and music for decades – there’s an easy way to add them as well.

The problem with this approach – Skydrive client will happily sync existing files, but will pass on any new ones added after initial sync. This happens because it cannot detect changes in symlinked folders. If you regularly shutdown/startup your machine – it’s not a problem, when client is restarted it rescans entire content for the changes – and follows symlinks as well.

But if your machine is “always on” e.g. a server there is an easy way as well. Just create an empty folder inside of a “real” Skydrive folder and delete it right away. This, similar to restart, will force Skydrive client to rescan entire content and sync with the cloud. Folder creation can be automated (a batch run on schedule for example) so you will always be in sync.

TSQL: work with yyyy-mm-dd date format in British English

If you work with SQL Server that is set to use UK (British English) format you may experience a strange behavior: when you try to assign a date that is in ‘yyyy-mm-dd’ format to a DateTime variable or insert it into a DateTime column – an error is thrown

The conversion of a varchar data type to a datetime data type resulted in an out-of-range value

or similar. Or even worse – no error is thrown, but an incorrect date is inserted. This is happening because even though ‘yyyy-mm-dd’ looks like universal ISO format, a UK SQL Server interprets it as ‘yyyy-dd-mm’. So a date like ‘2011-07-21’ will throw the above error, but the date ‘2011-08-01’ will be stored as ‘January 8, 2001’ instead of expected ‘August 1, 2011’.

To alleviate this problem simple add a time part to your date – make the format ‘yyyy-mm-ddThh:mm:ss’. So the dates above will become ‘2011-07-21T00:00:00’ and ‘2011-08-01T00:00:00’ and be interpreted correctly by SQL Sercer

Solution for “Operation is not valid due to the current state of the object” error

Typically this happens when AJAX controls are involved (Microsoft’s UpdatePanel or others that utilize AJAX POST requests.) The error may be displayed outright or, if nothing is shown on the UI – logged in the Event Viewer. In any case you will get a message similar to:

0x800a139e – Microsoft JScript runtime error: Sys.WebForms.PageRequestManagerServerErrorException: Operation is not valid due to the current state of the object

Issue happens because Microsoft Security Update MS11-100 limits number of keys in Forms collection during HTTP POST request. To alleviate this problem you need to increase that number.

This can be done in your application Web.Config in the <appSettings> section (create the section directly under <configuration> if it doesn’t exist). Add 2 lines similar to the lines below to the section:

<add key="aspnet:MaxHttpCollectionKeys" value="2000" /">
<add key="aspnet:MaxJsonDeserializerMembers" value="2000" /">

The above example set the limit to 2000 keys. This will lift the limitation and the error should go away.

VB for Android

Found this gem today:

Basic 4 Android

It’s a Visual Basic IDE environment for developing Android apps. But unlike other similar solutions it does not require bloated runtime running on the device, Basic4Android easily compiles native APK app.

Don’t learn Java, utilize your existing Visual Basic skills instead. And the community of thousands of developers can be a huge help as well.

Also you’re in luck today. Download the trial, play around with it and if you like it – use discount code “bvqbet” to get 50% off any version! Here’s how:

  1. Visit purchase link: http://www.basic4ppc.com/android/purchase.html
  2. Select Plimus as your checkout option
  3. Enter coupon code bvqbet in the coupon code field
  4. Profit! You get a 50% discound off a regular price

Happy coding!

Solution for ASP.NET access to temporary folder denied error

Scenario: You’re trying to run an ASP.NET application when suddenly an error is thrown similar to this:

Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: CS0016: Could not write to output file ‘c:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\……..\………\some_code.dll’ — ‘Access is denied. ‘

You gave that folder all possible permissions imaginable and still the error persist. What the? Continue reading →