Support SmartEnums

[mkalinski93]

Hello,

I wanted to submit a feature request for strongly typed enumerations, such as SmartEnum from Ardalis.

SmartEnums, or enhanced enums, have several advantages and can be a good alternative to default enumerations within data controls such as DataGrid, SelectBoxes and so on.

SmartEnums can be integrated into EntityFramework Core with conversions

protected override void OnModelCreating(ModelBuilder builder)
{
    base.OnModelCreating(builder);

    builder.Entity<Policy>()
        .Property(p => p.PolicyStatus)
        .HasConversion(
            p => p.Value,
            p => PolicyStatus.FromValue(p));
}

In the DevExpress Support Center, I have asked for help and Andrew did a great start on implementing this function

 DevExtreme.AspNet.Data.Helpers.CustomFilterCompilers.RegisterBinaryExpressionCompiler(info => {
    if (info.AccessorText.Contains(".") && info.Operation == "=" && info.Value is Int64) {
        string accessorText = info.AccessorText.Substring(0, info.AccessorText.IndexOf("."));
        var memberExpr = Expression.PropertyOrField(info.DataItemExpression, accessorText);
        var memberType = memberExpr.Type;
        if (typeof(Ardalis.SmartEnum.SmartEnum<>).MakeGenericType(memberType).IsAssignableFrom(memberType)) {
            return Expression.MakeBinary(
                ExpressionType.Equal,
                Expression.Convert(Expression.Convert(memberExpr, typeof(object)), typeof(long)),
                Expression.Constant(info.Value)
            );
        }
    }
    return null;
});

The problem is that it may cannot covers all possible scenarios.
The key solution would be a native integration in the DevExtreme.AspNet.Data library.

By the way, SmartEnums can also be integrated within DevExpress XPO using a custom ValueConverter

public class ProductStateConverter : ValueConverter {
        public override Type StorageType => typeof(int);

        public override object ConvertFromStorageType(object value) {
            int.TryParse(value.ToString(), out int number);
            return ProductState.TryFromValue(number, out ProductState retVal) ? retVal : null;
        }

        public override object ConvertToStorageType(object value) {
            if (value is ProductState ruleType)
                return ruleType.Value;
            return null;
        }
    }