Using OpenEdge holder classes

In ProxyGen, if you specify that a supported value type parameter or return value can have the Unknown value (?), and you have chosen to use holder classes, the method is defined with the corresponding holder class; otherwise the parameter is defined using the .NET value type.

The following is an example of a C# proxy method signature that does not support Unknown value (?) for the first and third parameters:

foo(int i, string s, bool b)

The following is an example of a C# proxy method that allows all the parameter values to have Unknown value (?), using holder classes where necessary:

foo(IntHolder i, string s, BooleanHolder b)

For each ABL data type that maps to a .NET value type, there is a Holder class. These Holder classes belong to the Progress.Open4GL namespace and extend the Progress.Open4GL.Holder class, as shown in the following table.

Table 5. Holder class definitions
Class	Constructors	Property
BooleanHolder	BooleanHolder( ) BooleanHolder(bool value)	System.Boolean BooleanValue;
DateHolder	DateHolder( ) DateHolder(System.DateTime value)	System.DateTime DateValue;
DecimalHolder	DecimalHolder(decimal value) DecimalHolder(double value)	System.Decimal DecimalValue;
IntHolder	IntHolder( ) IntHolder(int value)	System.Int32 IntValue;
LongHolder	LongHolder( ) LongHolder(long value)	System.Int64 LongValue;

The property specified in the above table allows you to set and get a value with the .NET value type for which it is defined. These classes all contain two additional properties that allow you to set and test for null:

Value — To which you can set or get null, which corresponds to setting or getting the Unknown value (?) for an ABL primitive type.

isNull — A System.Boolean property that returns true if the Value property of the holder class is set to null.

The following table shows ABL primitive types that have a default .NET value-type mapping that cannot accept Unknown value (?). To accept the Unknown value (?), these ABL primitive types are mapped to holder classes in the Progress.Open4GL namespace, as shown in the table.

Table 6. ABL primitive type to holder class mappings
This ABL primitive type...	Maps to this holder class...
DATE DATETIME DATETIME-TZ	Progress.Open4GL.DateHolder
DECIMAL	Progress.Open4GL.DecimalHolder
INT64	Progress.Open4GL.LongHolder
INTEGER	Progress.Open4GL.IntHolder
LOGICAL	Progress.Open4GL.BooleanHolder
RECID	Progress.Open4GL.LongHolder