Function to Load Enum-Typed Properties from Database

re: Function to Load Enum-Typed Properties from Database

Yang — Tue, 24 Apr 2007 21:05:01 GMT

Be careful about the performance of enum operations.

re: Function to Load Enum-Typed Properties from Database

PaulWilson — Fri, 13 Apr 2007 10:02:25 GMT

You can call Enum.IsDefined in the helper function first to guarantee a valid value, and if it fails then throw an exception. The same problem occurs with the simple cast syntax, so at least using a helper function makes it easier to add extra things like this when you find it is needed.

re: Function to Load Enum-Typed Properties from Database

Didasoft — Fri, 13 Apr 2007 06:29:39 GMT

all these helper function can not ensure valid value of enum.

at .net 2.0,

MyEnum test = ToEnum<MyEnum>(value);

support MyEnum only have two enum value, and the value is 10, no exception will throw. So i don't know MyEnum test now have a invalid value.

re: Function to Load Enum-Typed Properties from Database

Dave T — Thu, 12 Apr 2007 16:26:40 GMT

I would throw something like this into your helper:

System.Diagnostics.Debug.Assert(typeof(T).IsEnum);

re: Function to Load Enum-Typed Properties from Database

PaulWilson — Tue, 10 Apr 2007 20:37:51 GMT

As for the usage, consider an enum named MyEnum and a variable of that enum type that you want to load from an int value, possibly one you've stored in the database -- just do the following:

MyEnum test = ToEnum<MyEnum>(value);

As for the direct cast, that's a good question, and I could have sworn I'd tried that many times and it didn't work -- although it did just now in my test. Maybe I'm thinking of a limitation I encountered in .net v1 that I've been working around -- but maybe I'm wrong there as I didn't retest that assumption. Oh well, it seems that its not necessary for .net v2 at any rate, and if you have generics then you have .net v2, so mute point I suppose.

Thanks for the comments.

re: Function to Load Enum-Typed Properties from Database

Christian — Tue, 10 Apr 2007 20:27:12 GMT

Can you demo the usage?

re: Function to Load Enum-Typed Properties from Database

Steven — Tue, 10 Apr 2007 20:20:00 GMT

I've been looking at the implementation of Enum.ToObject(Type, int) (using Lut'z Reflector, of course), but can't seem to think of a reason to use it. Why not cast the int directly to it's enum?

MyEnum = (MyEnum)typeValue;

re: Function to Load Enum-Typed Properties from Database

jayson knight — Tue, 10 Apr 2007 14:51:57 GMT

To further constrain the input for T, add a type constraint of where T: struct. You can't use : enum, so struct is the next best thing.

Another handy utility enum function I use quite often:

public static T ParseEnum<T>(string value) where T: struct

{

return (T)Enum.Parse(typeof(T), value, true);

}