System.InvalidOperationException: Cannot convert string value 'i' from the database to any value in the mapped 'ItemType' enum

Question

I want to use an enum in my model, but in the database its stored as the Description attribute value, how can I make EF core understand this?

public enum ItemType
{
    [Description("s")]
    Floor,
    
    [Description("i")]
    Wall
}

Model:

public class Item
{
    public int Id { get; set; }
    public ItemType Type { get; set; }
}

Mapping

modelBuilder.Entity<ItemDto>()
    .Property(e => e.Type)
    .HasConversion<string>();

Answer 1

As discussed in the comment, EF Core doesn't know how to convert/mapping the Enum value based on the DescriptionAttribute. You need to implement a Value Converter to perform the mapping.

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    var enumDescriptionMappingConverter = new ValueConverter<ItemType, string>(
        v => v.ToDescription(), 
        v => EnumExtensions.GetValueByDescriptionAttribute<ItemType>(v));

        modelBuilder.Entity<Model>()
            .Property(e => e.Type)
            .HasConversion(enumDescriptionMappingConverter);
}

The first argument in ValueConverter is which converts the Enum value to a string based on DescriptionAttribute (From model to DB).

The second argument in ValueConverter is which converts the stored DB (string) value to the Enum (From DB to model).

While, I implement the extension/helper methods that are necessary in your scenario.

public static class EnumExtensions
{
    public static string ToDescription(this Enum value)
    {
        var attribute = value.GetAttribute<DescriptionAttribute>();
        if (attribute == null)
            return value.ToString();

        return attribute.Description;
    }

    public static TEnum GetValueByDescriptionAttribute<TEnum>(string value)
        where TEnum : Enum
    {
        var enumDict = Enum.GetValues(typeof(TEnum))
            .Cast<TEnum>()
            .ToDictionary(k => k, v => v.ToDescription());

        return enumDict
            .Single(x => x.Value == value)
            .Key;
    }

    private static T GetAttribute<T>(this Enum value)
        where T : Attribute
    {
        Type type = value.GetType();
        MemberInfo[] memberInfo = type.GetMember(value.ToString());
        var attributes = memberInfo[0].GetCustomAttributes(typeof(T), false);

        return (T)attributes.FirstOrDefault();
    }
}