Example of a model class using C# based on domain-driven design principles, including attributes and behaviors.

Product.cs

public class Product
{
  // The attributes have private setters, meaning they can only be modified from within the class itself.
  public int Id { get; private set; }
  public string Name { get; private set; }
  public decimal Price { get; private set; }
  public DateTime CreatedAt { get; private set; }
  public DateTime? UpdatedAt { get; private set; }

  public Product(string name, decimal price)
  {
    ValidateName(name);
    ValidatePrice(price);

    Id = GenerateUniqueId();
    Name = name;
    Price = price;
    CreatedAt = DateTime.Now;
  }

  public void UpdateName(string newName)
  {
    ValidateName(newName);
    Name = newName;
    UpdatedAt = DateTime.Now;
  }

  public void UpdatePrice(decimal newPrice)
  {
    ValidatePrice(newPrice);
    Price = newPrice;
    UpdatedAt = DateTime.Now;
  }

  private void ValidateName(string name)
  {
    if (string.IsNullOrWhiteSpace(name))
    {
      throw new ArgumentException("Name cannot be empty or whitespace.");
    }
  }

  private void ValidatePrice(decimal price)
  {
    if (price <= 0)
    {
      throw new ArgumentException("Price must be greater than zero.");
    }
  }

  private int GenerateUniqueId()
  {
    // Logic to generate a unique identifier for the product
    // This can be based on database auto-increment, GUID, or other mechanisms
    // For simplicity, we'll use a random number for the example
    return new Random().Next();
  }
}