Using a nullable enum and StringEnumFieldConverter

Hi everyone - usual disclaimer: very new to LS etc. etc.:

Using LightSpeed4 Professional and I'm playing around with converting a column to an enum as outlined here: http://www.mindscapehq.com/documentation/lightspeed/Working-with-Models-in-the-Visual-Designer/enums-and-other-user-defined-types

Scenario

Table Session has a column ApplicationCode, which is a string simply representing the name of the application e.g. "App1", "App2".

I have created a ApplicationConfiguration.ApplicationCode enum with the permitted values.

I have a User Defined Type set up in my model called ApplicationCodeEnum, originally set up following the 'Add an Enum Type to the Designer', with the CLR TypeName of ApplicationConfiguration.ApplicationCode and ConverterType of Mindscape.LightSpeed.FieldConverters.StringEnumFieldConverter<ApplicationConfiguration.ApplicationCode>

Problem

Session.ApplicationCode is nullable/optional.

When I run the code in the scenario where the Session.ApplicationCode column is null, the StringEnumFieldConverter can't figure out how to convert System.DBNull into a string.

[InvalidCastException: Unable to cast object of type 'System.DBNull' to type 'System.String'.]
   Mindscape.LightSpeed.FieldConverters.FieldConverter`2.€(Object ) +35
   Mindscape.LightSpeed.Model.FieldModel.<CreateValueSetter>b__55(IDataProviderAdapter , Object , Object[] , Int32 ) +71
   Mindscape.LightSpeed.Model.FieldModel.Materialize(IDataProviderAdapter , Object , Object[] , Int32& ) +262

[LightSpeedException: Unable to materialize field [ApplicationCode] on type [MyApp.Model.Session]: field is type 'MyApp.Model.ApplicationConfiguration+ApplicationCode' but database returned type 'System.DBNull'. Check your table has an Id column and that your mappings are correct. See inner exception for details.]
   Mindscape.LightSpeed.Model.FieldModel.Materialize(IDataProviderAdapter , Object , Object[] , Int32& ) +712
   ...blah blah

I have tried without joy.

• Setting the Session.ApplicationCode column to Nullable in the model.
• Setting ApplicationCodeEnum CLR TypeName and ConvertType to use a type of ApplicationConfiguration.ApplicationCode? instead Setting
• ApplicationCodeEnum IsValueType to False for kicks

How can I convince lightspeed or the converter that DBNull is okay? Is the only solution to write my own converter ala http://www.mindscapehq.com/documentation/lightspeed/Working-with-Legacy-Databases/Mapping-Database-Types-to-Domain-Types ?

Many thanks for any help you can provide!

StringEnumFieldConverter doesnt support nullables so you will need to implement a custom converter so you can use a nullable enum on your properties.

Here is the code for the current one, you should adapt this by making it deal with instead of which will allow you to support having a System.DBNull passed in. You can then check if TEnum is defined as nullable and if so if the value being passed in is System.DBNull then return null, otherwise use the existing logic for calling Enum.Parse().

public class StringEnumFieldConverter<TEnum> : FieldConverter<string, TEnum>
{
  protected override TEnum ConvertFromDatabase(string databaseValue)
  {
    return (TEnum)(Enum.Parse(typeof(TEnum), databaseValue, true));
  }

  protected override string ConvertToDatabase(TEnum value)
  {
    return Enum.GetName(typeof(TEnum), value);
  }
}

Let me know how you get in with this :)

Jeremy

Thanks Jeremy - good to know it wasn't worth trying to continue down a useless path! Custom converter and we're away. Appreciate the quick reply.