Convert enum underlying value to string without knowing the enum type

Question

I have a method taking an object and returning it in string format with some stuff depending on the type. For example:

ConvertObjectToSQL(1); // "1"
ConvertObjectToSQL("Foo"); // "'Foo'"
ConvertObjectToSQL(DateTime.Now); // "'2017/02/22 00:00:00'"

My problem occurs when I provide an enum to that method. I want my method to act as if I provided it the enum underlying type. Of course, my method is called in a context where I can't possibly know the enum type.

In the first place, here is what I did:

private string ConvertObjectToSQL(object obj)
{
    if (obj == null)
    {
        return "NULL";
    }
    else if (obj is DateTime)
    {
        return "'" + obj.ToString() + "'";
    }
    else if (obj is string)
    {
        return "'" + obj.ToString().Replace("'", "''") + "'";
    }

    return obj.ToString();
}

But if my enum is:

enum FooEnum : int { Foo = 0, Bar = 1 }

If want :

ConvertObjectToSQL(FooEnum.Foo); // "0"
ConvertObjectToSQL(FooEnum.Bar); // "1"

But it actually returns:

ConvertObjectToSQL(FooEnum.Foo); // "Foo"
ConvertObjectToSQL(FooEnum.Bar); // "Bar"

So I end up with a new else if doing the job:

else if (obj is Enum)
{
    var baseType = Enum.GetUnderlyingType(obj.GetType());
    return Convert.ChangeType(obj, baseType).ToString();
}

My question is: can I avoid reflexion here? Because this methods is called a lots of times.

@Luminous_Dev: that may not do what is desired if the enum isn't based on int... — Chris
– Chris, Commented Feb 22, 2017 at 9:56
@Luminous_Dev: as I said: my method is called in a context where I can't possibly know the enum type. So as said @Chris, the enum is not necessarily based on int. — fharreau
– fharreau, Commented Feb 22, 2017 at 9:59
I have to point out a question here though that you should probably not do some of this at all, you're seemingly constructing SQL by concatenating pieces, you may want to look into using parameters instead. — Lasse V. Karlsen
– Lasse V. Karlsen, Commented Feb 22, 2017 at 10:07
You can always craft delegates and cache these depending on type, this seems to be slightly faster, not by much, but slightly. — Lasse V. Karlsen
– Lasse V. Karlsen, Commented Feb 22, 2017 at 10:43

Magnus · Accepted Answer · 2017-02-22 10:44:34Z

1

Since enums implement IConvertable we can convert it to a Decimal (which will cover the size all integral types) and then to a string.

private string ConvertObjectToSQL(object obj)
{
    if(obj is Enum)
    {
        return Convert.ToDecimal(obj).ToString();
        //return ((Enum)obj).ToString("D"); Or this
    }
    return "";
}

edited Feb 22, 2017 at 10:44

answered Feb 22, 2017 at 10:00

Magnus

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10 Comments

fharreau Over a year ago

That won't work because I do not know the base type of the enum. In my example, I choose int but it could be char for example

Lasse V. Karlsen Over a year ago

Is it legal in IL to have an enum based on char? C# only allows the numeric integral types.

Magnus Over a year ago

Do you want an numeric value back?

Lasse V. Karlsen Over a year ago

He has already said what he want, he want the numeric value as a string, no matter which underlying type is used for the int, and an int can be based on byte, sbyte, and so on, in which case the cast to (int) will fail.

pinkfloydx33 Over a year ago

Why not just use the enum string format specifier "D"?

|

Reid A · Accepted Answer · 2018-06-22 17:47:14Z

You can create a delegate to get the underlying type value and cache it.

''' <summary>
''' Caches an enum underlying value getter delegate.
''' </summary>
''' <typeparam name="TEnum">Enum type</typeparam>
Public Class CachedEnumUnderlyingValueAccess(Of TEnum)
    Private Shared underlyingTypeValueGetter As Func(Of TEnum, Object) = CreateUnderlyingTypeValueGetter()

    Private Shared Function CreateUnderlyingTypeValueGetter()
        Dim enumUnderlyingType As Type = [Enum].GetUnderlyingType(GetType(TEnum))
        Dim enumParameter As ParameterExpression = Expression.Parameter(GetType(TEnum))
        'Convert the enum parameter to its underlying type, then convert it to an Object
        Dim conversionExpression As Expression(Of Func(Of TEnum, Object)) = Expression.Lambda(Expression.Convert(Expression.Convert(enumParameter, enumUnderlyingType), GetType(Object)), enumParameter)
        Return conversionExpression.Compile()
    End Function

    Public Shared Function GetEnumUnderlyingValue(val As TEnum) As Object
        Return underlyingTypeValueGetter.Invoke(val)
    End Function
End Class

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