Description of data type conversion and an example of its use

Properties of data classes can have the different type as standard .Net framework (such as System.Int32 — int in C#, System.String — string in C#) and custom (any user, not .Net-type).

Standard types is converted to the data services to store types some predefined way, for example, System.Int32 in LONG, System.String in VARCHAR. However, data services does not knows» qmo, how to evaluate the value of some custom type (in other words, what type the value in storage). Therefore, the value of the user-defined type must be the value of the standard type .Net and back, and with the value of a standard type data service already» «will understand.

How exactly such a cast must be performed by a specific data service, specified user-defined type attribute StoreInstancesInTypeAttribute. The details include: type of service data and a standard type to be cast.

From a user-defined type requires the following:

  • Support for explicit (explicit) or implicit (implicit) conversion to standard types.
  • Support for explicit (explicit) or implicit (implicit) the inverse transformation from the standard type.
  • Method overloading ToString().

Of course, if different data services require a cast to different types, it is necessary to repeatedly specify an attribute for each data service, and a user-defined type must support conversion for all types.

an Example of a custom type

[StoreInstancesInType(typeof(SQLDataService),typeof(decimal)))
public struct Деньги
{
	public class ParameterOutOfRangeException:Exception
	{
			public ParameterOutOfRangeException(){}
	}
	
	private int fieldРубли;
	private int fieldКопейки;
	
	public Деньги(int Руб,int Коп)
	{
			fieldРубли = 0;
			fieldКопейки = 0;
			Рубли = Руб;
			Копейки = Коп;
	}
	
	public int Рубли
	{
			get{return fieldРубли;}
			set
			{
					if (value>=0)
							fieldРубли = value;
			}
	}
	
	public int Копейки
	{
			get {return fieldКопейки;}
			set
			{
					if (value>=0 && value<100)
							fieldКопейки = value;
					else
							throw new ParameterOutOfRangeException();
			}
	}
	
	public static implicit operator decimal(Деньги value)
	{
			return (decimal)value.Рубли+((decimal)value.Копейки)/100;
	}
	
	public static implicit operator Деньги(decimal value)
	{
			return new Деньги((int)value,(int)((value-(int)value)*100));
	}
	
	public override string ToString()
	{
			return Рубли.ToString()+"RUB."+Копейки.ToString()+"COP.";
	}
}

Is also available example GitHub.

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