C#•5mo ago

✅ [AllowedValue] not doing anything

Why is my code allowing the name "Jimmy" ?

using System.ComponentModel.DataAnnotations;

public class Foo
{
    [AllowedValues(new object [] {"Bill", "Bob"}, "Entered illegal name")]
    public string Name { get; set; }
}

class Program
{
    public static void Main()
    {
        Foo f = new()
        {
            Name = "Jimmy" // works ???
        };
    }
}

using System.ComponentModel.DataAnnotations;

public class Foo
{
    [AllowedValues(new object [] {"Bill", "Bob"}, "Entered illegal name")]
    public string Name { get; set; }
}

class Program
{
    public static void Main()
    {
        Foo f = new()
        {
            Name = "Jimmy" // works ???
        };
    }
}

13 Replies

oke•5mo ago

The AllowedValues attribute seems to be for code clarity/readability, not actually enforcing the value. But, it's a property, so you can just implement that check in the setter.

oke•5mo ago

It would be nice if they put something like that in the documentation though. https://learn.microsoft.com/en-us/dotnet/api/system.componentmodel.dataannotations.allowedvaluesattribute?view=net-8.0

AllowedValuesAttribute Class (System.ComponentModel.DataAnnotations)

Specifies a list of values that should be allowed in a property.

oke•5mo ago

It just says "specifies a list of values that should be allowed"

Anton•5mo ago

There's got to be at least an analyzer for this It would pretty easy to detect -- just look at constructors where that property is assigned a constant. Roslyn detects that automatically. More complex rules will have to be coded manually though

jcotton42•5mo ago

@Jason_Bjorn all of DataAnnotations is for things like GUIs and ASP.NET when doing input validation. They have no meaning to the compiler.

Jason_BjornOP•5mo ago

the docs are pretty bleak for that one would be nice if this was documented but thank you

jcotton42•5mo ago

It is. Attributes interpreted by the compiler are documented as such.

Jason_BjornOP•5mo ago

Where does it say that

jcotton42•5mo ago

What do you mean? If the docs for an attribute don’t say “the compiler looks at this attribute” (paraphrasing), the compiler won’t be looking at the attribute.

oke•5mo ago

i think this one is mostly on microsft (or the team of people who update the docs) it would be nice if there were a tag or something that clarified that this does nothing another thing i noticed for this, even if the attribute actually did something, this still wouldnt work as intended because the constructor only takes an array of objects and notes nothing about the last being an error message so it could be rewritten as

public class Foo
{
    [AllowedValues("Bill", "Bob")]
    public string Name { get; set; }
}

public class Foo
{
    [AllowedValues("Bill", "Bob")]
    public string Name { get; set; }
}

Jason_BjornOP•5mo ago

thank you

Unknown User•5mo ago

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✅ [AllowedValue] not doing anything