Entity Framework & SQL Server CE problem

The SQL Server Compact Edition throws a very unhelpful SqlCeException exception with the message:

"A parameter is missing. [ Parameter ordinal = 1 ]"

when using the entity framwork SaveChanges() method if you set a decimal property to a value with more decimal places than the database column has been configured to store.

For example, if you have a database table "header" with a Numeric 18/3 column "Height" and execute the following code, the "A parameter is missing" will be thrown.

  EntityFrameworkSQLCEEntities entities = new

EntityFrameworkSQLCEEntities();

            

  Header header = Header.CreateHeader(Guid.NewGuid(), "Test");

  header.Height = Convert.ToDecimal(3.4555);

  //header.Height = Decimal.Round(Convert.ToDecimal(3.4555), 3);

  entities.AddToHeader(header);

  entities.SaveChanges();

Rounding the decimal to the supported number of decimal places prior to setting the property "fixes" this problem but couldn't this be better handled by the Entity Framework and/or SQL Server Compact Edition?

App.Config DataDirectory macro

By default, the |DataDirectory| macro is substituted at run-time with the folder that contains the exe.  You can override this default by changing the setting the "DataDirectory" property on the app domain as follows:

   AppDomain.CurrentDomain.SetData("DataDirectory", thePath );

Installing & using SQL Server Compact Edition data files

I've been writing a program that uses the SQL Server Compact Edition for data storage.

I configure the program (via the application config file in the set-up project) to access the SQL data file (SDF file) from the programs installation folder.  This all worked without problem on my XP & Vista PCs.

However, when installed on another Vista Laptop, my application was denied access to the SDF file and was unable to run.  This turned out to be because the laptop had UAC turned on.

This page  on stackoverflow has some solutions to this problem.  The simplest of which is to change the application to a "Full Trust" application.  You can do this in Visual Studio 2008 from the application security property page. Just check the "Enable ClickOnce Security Settings" and then select "This is a full trust application".

BTW, I've tested this on Windows 7 with UAC set on its default ("Notify me when programs try to make changes to my computer").

Formatted TimeSpan WPF Binding

The .Net TimeSpan object is displayed in a fixed format when bound to a WPF control. If you need to display a TimeSpan with a custom format you need to do this via a converter class that derives from IValueConverter.

class TimeSpanConverter : IValueConverter

{

public object Convert(object value, Type targetType,

object parameter, System.Globalization.CultureInfo culture)

{

TimeSpan timeSpan = (TimeSpan) value;

String result = String.Empty;

if ( timeSpan != null )

{

result = String.Format(

"{0:D2}:{1:D2}:{2:D2}:{3:D2}.{4:D1}",

timeSpan.Days, timeSpan.Hours,

timeSpan.Minutes, timeSpan.Seconds,

(int) Math.Round( timeSpan.Milliseconds/100.0));

}

return result;

}

public object ConvertBack(object value, Type targetType,

object parameter, System.Globalization.CultureInfo culture)

{

return null;

}

}

You can create an instance of the Converter class in the Windows resources as follows:

Window.Resources

srm:TimeSpanConverter x:Key="TimeSpanConverter" /srm:TimeSpanConverter

Window.Resources

and use this converter in the binding with the following XAML

GridViewColumn Header="Duration" DisplayMemberBinding=

"{Binding Path=Duration, Converter={StaticResource TimeSpanConverter}}"

Update

I now use the following which has support for an option ConvertParameter:

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {                       
            String result = String.Empty;
            if ( value is TimeSpan )
            {
                TimeSpan timeSpan = (TimeSpan) value;
                if (timeSpan != TimeSpan.Zero)
                {
                    if (parameter == null || !(parameter is string))
                        result = String.Format("{0:D2}:{1:D2}:{2:D2}:{3:D2}.{4:D1}",
                                    timeSpan.Days, timeSpan.Hours, timeSpan.Minutes, timeSpan.Seconds, (int)Math.Round(timeSpan.Milliseconds / 100.0));
                    else
                    {
                        DateTime time = DateTime.Today;
                        time = time.Add(timeSpan);
                        result = time.ToString((string)parameter);
                    }
                }
            }
            return result;
        }

XAML:

Binding="{Binding Path=Duration, ConverterParameter=H:mm:ss.f, Converter={StaticResource TimeSpanConverter}}"