ASP0037: [ValidatableType] cannot be used in generated code

	Value
Rule ID	ASP0037
Category	Usage
Severity	Warning

Cause

The ValidatableTypeAttribute attribute is applied to a type declared in generated code, such as code generated from a Razor (.razor) file.

Rule description

The validation source generator can't inspect another source generator's output. Applying [ValidatableType] to a type in generated code has no effect, so the type isn't included in generated validation metadata.

For example, declaring the following model in a Razor component's @code block produces this diagnostic:

@code {
    [ValidatableType]
    public class Order
    {
        [Required]
        public string? CustomerName { get; set; }
    }
}

How to fix violations

Move the type to a regular C# (.cs) file and apply [ValidatableType] there:

[ValidatableType]
public class Order
{
    [Required]
    public string? CustomerName { get; set; }
}

For more information, see Validation in ASP.NET Core.