Validate or Override FluentNhibernate Database to Enum mapping

Question

I have a database which is accessed by multiple systems. Ours reads a table using Fluent Nhibernate and Automapping.

One of the columns is a string representing an enum. In most installations this is fine, but every now and then another system will persist an invalid value. How can I catch these invalid values and either convert or ignore them?

Example:

Database Table:
ID  MyEnum
0   "One"
1   "Two"
2   "Invalid"

MyEnum
{
  One,
  Two
}

I'm already using IAutoMappingOverride with my model, is there anyway to pass a function to the mapper to do validation/conversion (say I wanted to convert any unknowns to MyEnum.One)? Or is there a simpler way that I'm missing?

Where I got to was using a combination of @Firo's answer and the answers here and here

class SafeEnumType<T> : ImmutableUserType where T : struct
{
    public override object NullSafeGet(IDataReader rs, string[] names, object owner)
    {
        T value;
        if (Enum.TryParse((string)rs[names[0]], out value))
            return value;
        else
            return default(T);
    }

    public override void NullSafeSet(IDbCommand cmd, object value, int index)
    {
        NHibernateUtil.String.NullSafeSet(cmd, value.ToString(), index);
    }

    public override Type ReturnedType
    {
        get { return typeof(T); }
    }

    public override SqlType[] SqlTypes
    {
        get { return new[] { SqlTypeFactory.GetString(100) }; }
    }
}

and adding

mapping.Map(x => x.Type).CustomType(typeof(SafeEnumType<EventType>));

to my AutomapOverride.Override() fn

score 1 · Accepted Answer · edited May 23 '17 at 12:10

In NHibernate there is IUserType which lets you define custom conversion code. here is a base class of mine which you can use because enums are immutable types

code

class SpecialEnumUserType : ImmutableUserType
{
    public override object NullSafeGet(IDataReader rs, string[] names, object owner)
    {
        TheSpecialEnum value;
        if (Enum.TryParse<TheSpecialEnum>((string)rs[names[0]], out value))
            return value;
        else
            return default(TheSpecialEnum);
    }

    public override void NullSafeSet(IDbCommand cmd, object value, int index)
    {
        NHibernateUtil.String.NullSafeSet(cmd, value.ToString(), index);
    }

    public override Type ReturnedType
    {
        get { return typeof(TheSpecialEnum); }
    }

    public override SqlType[] SqlTypes
    {
        get { return new[] { SqlTypeFactory.GetString(50) }; }
    }
}

and convention to apply them to every enum property

class EnumHandlingConvention : IPropertyConvention
{
    public void Apply(IPropertyInstance instance)
    {
        if (instance.Type == typeof(TheSpecialEnum))
        {
            instance.CustomType<SpecialEnumUserType>();
        }
    }
}

OK, it's not very neat for my purposes, though. Is there an easier way to intercept the DB to object step for a particular property? — Byron Ross, Oct 14 '13 at 06:36
that is the easiest way. What's your exact problem with the IUserType? — Firo, Oct 14 '13 at 08:51
specifically wanted to only handle one particular enum, if you edit your answer I'll accept it, thx. — Byron Ross, Oct 15 '13 at 23:06

Validate or Override FluentNhibernate Database to Enum mapping

1 Answers1