cat_cafe/cat_cafe/Entities/Cat.cs

using System.ComponentModel.DataAnnotations;

namespace cat_cafe.Entities
{
    public class Cat
    {
        public long Id { get; set; }
        public string? Name { get; set; }
        [Required]
        public int Age { get; set; } = 0;

        public string Meow() { return "meow"; }
    }
}