How to add attributes to a base class's properties

Declare the property in the parent class as virtual:

public class MyModelBase
{
    public virtual string Name { get; set; }
}

public class MyModel : MyModelBase
{
    [Required]
    public override string Name { get; set; }

    public string SomeOtherProperty { get; set; }
}

Or you could use a MetadataType to handle the validation (as long as you're talking about DataAnnotations...otherwise you're stuck with the example above):

class MyModelMetadata
{
    [Required]
    public string Name { get; set; }

    public string SomeOtherProperty { get; set; }
}

[MetadataType(typeof(MyModelMetadata))]
public class MyModel : MyModelBase
{
    public string SomeOtherProperty { get; set; }
}

Try using a metadata class. It's a separate class that is referenced using attributes that lets you add data annotations to model classes indirectly.

e.g.

[MetadataType(typeof(MyModelMetadata))]
public class MyModel : MyModelBase {
  ... /* the current model code */
}


internal class MyModelMetadata {
    [Required]
    public string Name { get; set; }
}

ASP.NET MVC (including Core) offers similar support for its attributes like FromQuery, via the ModelMetadataTypeAttribute.

I note that none of these answers actually call the base Name property correctly. The override should write something like the following, in order that you don't have a separate value for the new property.

public class MyModelBase
{
    public virtual string Name { get; set; }
}

public class MyModel : MyModelBase
{
    [Required]
    public override string Name { get { return base.Name; } set { base.Name = value; }

    public string SomeOtherProperty { get; set; }
}