C#•11mo ago

✅ Does anyone know why Validator.ValidateObject only validates properties and not fields?

And is there a way to make it work with fields?

31 Replies

Angius•11mo ago

Why validate fields? They're an implementation detail

So... because that's how it's written. Deep down in the bowels of the the validate object code you have ...

 private static ICollection<KeyValuePair<ValidationContext, object>> GetPropertyValues(object instance, ValidationContext validationContext) {

            PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(instance);
            List<KeyValuePair<ValidationContext, object>> items = new List<KeyValuePair<ValidationContext, object>>(properties.Count);
            foreach (PropertyDescriptor property in properties) {
                ValidationContext context = CreateValidationContext(instance, validationContext);
                context.MemberName = property.Name;

                if (_store.GetPropertyValidationAttributes(context).Any()) {
                    items.Add(new KeyValuePair<ValidationContext, object>(context, property.GetValue(instance)));
                }
            }
            return items;
        }

 private static ICollection<KeyValuePair<ValidationContext, object>> GetPropertyValues(object instance, ValidationContext validationContext) {

            PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(instance);
            List<KeyValuePair<ValidationContext, object>> items = new List<KeyValuePair<ValidationContext, object>>(properties.Count);
            foreach (PropertyDescriptor property in properties) {
                ValidationContext context = CreateValidationContext(instance, validationContext);
                context.MemberName = property.Name;

                if (_store.GetPropertyValidationAttributes(context).Any()) {
                    items.Add(new KeyValuePair<ValidationContext, object>(context, property.GetValue(instance)));
                }
            }
            return items;
        }

NB: I redacted some silverlight code from the above. So validate object won't ever know about fields. DataAnnotations leaves a lot to be desired. Looking at the source, you may be able to use Validateor.ValidateValue; but I"m not certain.

Angius•11mo ago

The same way you don't test private methods, you don't validate private fields And if it's public it should be a property anyway And those can be validated

Mayor McCheese•11mo ago

I'm assuming he means public int SomeField; which yeah, I also fundamentally disagree with, use a property.

LegionOP•11mo ago

I guess im off the mind set that one should use a field until they need it to be a property, which is why im a little confused by this limitation

Angius•11mo ago

You're of the wrong mindset, then

Mayor McCheese•11mo ago

Annoyingly there is this, where validation attributes can be on fields.

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false)]
    [SuppressMessage("Microsoft.Design", "CA1019:DefineAccessorsForAttributeArguments", Justification = "We want it to be accessible via method on parent.")]
    [SuppressMessage("Microsoft.Performance", "CA1813:AvoidUnsealedAttributes", Justification = "We want users to be able to extend this class")]
    public class RangeAttribute : ValidationAttribute {

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false)]
    [SuppressMessage("Microsoft.Design", "CA1019:DefineAccessorsForAttributeArguments", Justification = "We want it to be accessible via method on parent.")]
    [SuppressMessage("Microsoft.Performance", "CA1813:AvoidUnsealedAttributes", Justification = "We want users to be able to extend this class")]
    public class RangeAttribute : ValidationAttribute {

There's not a large cost to use a property; introducing a property later is a breaking change that is hard to fix.

LegionOP•11mo ago

a little salty :/

Mayor McCheese•11mo ago

but not wrong

LegionOP•11mo ago

i wasnt aware, is that because of reflection differences?

Angius•11mo ago

Encapsulation, changing it is breaking

Mayor McCheese•11mo ago

yesn't, if you're deploying your whole app it's not a breaking change if you're not using reflection, if you are using reflection it may be a breaking change; if you're deploying using multiple assemblies and only a partial deployment then it's a breaking change.

LegionOP•11mo ago

fair enough, i'll switch them over

Angius•11mo ago

Also, for purely pragmatic purposes, every library will assume properties are public and fields are private Fields don't get serialized to JSON, for example Fields cannot be used in DI Etc.

LegionOP•11mo ago

thats good to know, untill now i kinda felt that { get; set; } was essentially a more verbose way of declaring a field unless you implemented them

Mayor McCheese•11mo ago

properties create methods, like <GetName()> and <SetName(string value)>; and fields don't; so a partial deployment creates a breaking change when updated from a field to a property.

Angius•11mo ago

$getsetdevolve

MODiX•11mo ago

class Foo
{
    private int _bar;

    public int GetBar()
    {
        return _bar;
    }

    public void SetBar(int bar)
    {
        _bar = bar;
    }
}

class Foo
{
    private int _bar;

    public int GetBar()
    {
        return _bar;
    }

    public void SetBar(int bar)
    {
        _bar = bar;
    }
}

can be shortened to

class Foo
{
    private int _bar;

    public int GetBar() => _bar;

    public void SetBar(int bar) => _bar = bar;
}

class Foo
{
    private int _bar;

    public int GetBar() => _bar;

    public void SetBar(int bar) => _bar = bar;
}

can be shortened to

class Foo
{
    private int _bar;
    public int Bar {
        get { return _bar; }
        set { _bar = value; }
    }
}

class Foo
{
    private int _bar;
    public int Bar {
        get { return _bar; }
        set { _bar = value; }
    }
}

can be shortened to

class Foo
{
    private int _bar;
    public int Bar {
        get => _bar;
        set => _bar = value;
    }
}

class Foo
{
    private int _bar;
    public int Bar {
        get => _bar;
        set => _bar = value;
    }
}

can be shortened to

class Foo
{
    public int Bar { get; set; }
}

class Foo
{
    public int Bar { get; set; }
}

Mayor McCheese•11mo ago

you can declare more explicit getters and setters, that become the guts of methods like <GetName()>, let's say if you wanted to return a default value or something.

LegionOP•11mo ago

Kinda strange thing, type.GetProperties() does not return autoproperties, but GetFields() does unless theres something really buggy going on lol

MODiX•11mo ago

Angius

REPL Result: Success

using System.Reflection;

class Foo
{                                                                         public int A { get; set; }                                        }

typeof(Foo).GetProperties(BindingFlags.Instance | BindingFlags.Public).Select(p => p.Name)

using System.Reflection;

class Foo
{                                                                         public int A { get; set; }                                        }

typeof(Foo).GetProperties(BindingFlags.Instance | BindingFlags.Public).Select(p => p.Name)

Result: List<string>

[
  "A"
]

[
  "A"
]

Compile: 463.180ms | Execution: 59.138ms | React with ❌ to remove this embed.

Angius•11mo ago

For reasons unknown to me, you need to specify at least two flags: * Static or Instance * Public or NonPublic Otherwise, you get an empty array

LegionOP•11mo ago

i think its just a problem with my source generator

Angius•11mo ago

You're using reflections in a source generator?

LegionOP•11mo ago

no, im using a source generator to autofill some XML annotations, but the old generated file with the member is still a field apparently

Mayor McCheese•11mo ago

I feel like .... that didn't use to be the case?

Angius•11mo ago

I can see references to it on SO going as far back as 2013 Probably even earlier

Mayor McCheese•11mo ago

I might be conflating with something else with reflection, do you need to do that for attributes?

LegionOP•11mo ago

i fight a lot with the XmlSerializer, but anyway its a different issue :P how do i mark this as solved?

Pobiega•11mo ago

/close

LegionOP•11mo ago

thanks,

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Programming

✅ Does anyone know why Validator.ValidateObject only validates properties and not fields?