C# Object-Oriented Database – Object Oriented Data Structures in Database Driven Applications

I've started working for a company that maintains a small/medium sized commercial website. The website is written in c# asp.net, and uses SQL Server as a database. The structure of the code is very messy at the moment (for instance, ~5000 line Utility.cs file) so I want to move towards a better design on the asp.net side of the application.

I'm trying to figure out the right way to do this. My basic plan is to create a class for every logically distinct item in the application (mostly mapping 1-1 to database tables, but sometimes N-1 or 1-N). Then, I plan to have some static factory methods to instantiate these classes by querying the database. The developer should be able to manipulate the resultant object, and then use a UpdateDatabase() method to save the changes to the database.

For example, here is how an Email object would work:

public class Email {
    Guid userId;
    Guid emailId;
    String emailValueInitial = null;
    Sting emailValueNew = null;

    private Email();

    public static Email RetrieveEmail(Guid UserId, Guid EmailId) {
        // .. query
        return new Email(UserId,EmailId,emailValueInitial);            
    }

    public String EmailValue { 
        get {
            if (emailValueNew == null) return emailValueInitial;
            else return emailValueNew;             
        }
        set {
            emailValueNew = value;
        }
    }

    public bool Update() {
       // .. update database with value of emailValueNew or do nothing if it hasn't 
       // been changed
    }

}

Notes:

• I could update the database whenever a field is changed, but this is obviously inefficient.
• I don't know what to do in the event that the developer wants to insert a null value into the database – I suppose I need different concepts for 'null as variable not yet used' vs 'null as database value null'.

The above is a simple case. I'd also need some way of knowing about many-one relationships in tables. For instance, a User could work like this:

public class User {
    Guid userId;

    public Emails emails = new Emails(userId);

    private User(); // etc..

    public RetrieveUser();
    public CreateUser();

    public Update();
}

public class Emails {
    List<Email> emails = new List<Email>();

    Guid userId;

    public Emails(Guid userId); // etc..

    public bool CreateEmail(); // its convinient to create/delete from here
    public bool DeleteEmail(); // as I can enforce, say, minimum 1 email per user
}

These above are my first thoughts on how to solve this problem, but I've never done anything like this before, and I don't know what problems I might come across. I want to make a system that will be scaleable and easy to develop as we take on more programmers, so its really important to get the initial design correct.

What kind of design should I use in an object-orientated language to best represent and link with a database? What are important things to consider? Is there existing literature on this subject, or important libraries/constructs I have neglected?