Question

I am trying to work out the best way to design a class that has its properties persisted in a database. Let’s take a basic example of a Person. To create a new person and place it in the database, I want the DateOfBirth property to be optional (i.e. NULLable in the DB).

Here’s my sample code:

namespace BusinessLayer
{
    class Person
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public DateTime DateOfBirth { get; set; }
    }
}

I’m unsure as to whether the fields should be public or not. Should I do it like this:

class Program
{
    static void Main(string[] args)
    {
        Person person1 = new Person("Kate","Middleton",null);
    }
}

or like this:

class Program
{
    static void Main(string[] args)
    {
        Person person1 = new Person();
        person1.FirstName = "Kate";
        person1.LastName = "Middleton";
    }
}

I’m also wondering how I should be dealing with the optional properties of the class. Once the fields have been populated how do I then save them to the DB? I have a DatabaseComponenet class to save the information. How do I deal with the optional when saving to the database?

So, would I do something like this:

public int Save()
{
    int personId;
    personId = DatabaseComponent.InsertPerson(FirstName, LastName, DateOfBirth);
    return personId;
}

Thanks for any help! Some useful URLs on good class design would also be appreciated.

Answer 1

First, I’d put two distinct public constructor to Person:

namespace BusinessLayer
{
    class Person
    {
        public Person(string firstName, string lastName): this(firstName, lastName, DateTime.Now)
        {}

        public Person(string firstName, string lastName, DateTime birthDate)
        {
            FirstName = firstName;
            LastName = lastName;
            DateOfBirth = birthDate;
        }

        public string FirstName { get; set; }
        public string LastName { get; set; }
        public DateTime DateOfBirth { get; set; }
    }
}

this allows you to write both

var p = new Person("Marilyin", "Manson");
var p2 = new Person("Alice", "Cooper", new DateTime(...));

and

var p = new Person { FirstName="Marilyn", LastName="Manson" };

I can’t see why you should limit to only one form.

As for the DatabaseComponent I’d strongly suggest to write a method that allows you to save a Person instead of the signature you are implicitly declaring.

That’s because, should one day change the way a Person is defined, you’d probably have to change the code in each point you invoke Save() method. By saving just a Person, you only have to change the Save() implementation.

Don’t you plan to use an ORM by the way?