Storing NULL instead of blank string columns

While saving a collection with all the changes, how can i ensure that blank strings should go as NULLs? I am using linq, wpf, wcf.

I don't want to iterate for each record and each property of record to 开发者_高级运维put a null if blank.

You can use a IValueConverter class like following :: Below code is for double, you can stimulate the behavior for other types

public class DoubleNullFromStringConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value is double || value is double?) return value;
        return null;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null)
            return null;

        var strValue = value as string;
        if (strValue == null || strValue.Trim().Length == 0)
            return null; //allow empty strings and whitespaces

        double doubleValue = 0;
        if (double.TryParse(strValue, out doubleValue))
            return doubleValue;

        return value; //which will intenionally throw an error 
    }
}

Then Bind this to your control like following

<TextBox HorizontalAlignment="Left" Name="brokeragePaidText" VerticalAlignment="Top" Width="170" >
        <TextBox.Text>
            <Binding Source="{StaticResource insertTransaction}" Converter="{StaticResource DoubleNullFromStringConverter}" UpdateSourceTrigger="Explicit" Path="BrokeragePaid">
                <Binding.ValidationRules>
                    <ExceptionValidationRule/>
                </Binding.ValidationRules>
            </Binding>
        </TextBox.Text>
    </TextBox>

You could implement the [OnSerializing] event in your WCF DataContract to check for String.Empty and change it to null. EG:

[DataContract]
class MyDataStructure
{
    [DataMember]
    string Foo { get; set; }

    [OnSerializing]
    void OnSerializing(StreamingContext context)
    {
        if (Foo == String.Empty)
            Foo = null;
    }
}

And if you have a lot of string properties and don't want to write the code to test each, you could always use Reflection to loop through the class's properties.