Guidelines

Conversion hooks can only be used to convert a value from the data type used in an attribute to the data type used in the corresponding attribute implementation, and vice versa.

Only one input parameter and one output parameter are used. Other attribute implementations or table columns must not be used in a conversion hook. The parameter representing the attribute is always a string. The parameter representing the corresponding attribute implementation is declared on its domain.

The actual conversion is done in the public layer. So when using the protected interface within LN, only the domains as specified for the attribute implementations are used. For example, if you define a conversion hook for an enumerate, the attribute will have a string data type, but the attribute implementation will use the enumerate domain as its data type.

Standard data type conversions (see Standard Conversions) need not be implemented in a hook.