Designing Application Using Test Driven Development

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;

namespace DomainObjects
{
    public class SQLDataAccess
    {
        private static string connectionString = "Server=localhost;Database=School;Trusted_Connection=true";


        public static void UpdatePerson(Person person)
        {
            string query = @"UPDATE Persons SET FirstName = @FirstName, LastName = @LastName, DOB = @DOB, DateModified = GETDATE()
                            WHERE PersonID = @PersonID";

            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                SqlCommand myCommand = new SqlCommand(query, conn);
                myCommand.Parameters.AddWithValue("@FirstName", person.FirstName);
                myCommand.Parameters.AddWithValue("@LastName", person.LastName);
                myCommand.Parameters.AddWithValue("@DOB", person.DOB);
                myCommand.Parameters.AddWithValue("@PersonID", person.Id); 

                
                conn.Open();
                myCommand.ExecuteNonQuery(); 
            }
        }
 

        public static void SaveAddress(IList<Address> addresses)
        {
            string query = "INSERT INTO Addresses(PersonID,Street) VALUES(@PersonID, @Street) SELECT SCOPE_IDENTITY()";

            foreach (Address address in addresses)
            {

                using (SqlConnection conn = new SqlConnection(connectionString))
                {
                    SqlCommand myCommand = new SqlCommand(query, conn);
                    myCommand.Parameters.AddWithValue("@PersonID", address.Person.Id);
                    myCommand.Parameters.AddWithValue("@Street", address.Street);

                    conn.Open();
                    address.Id = Convert.ToInt32(myCommand.ExecuteScalar());
                    myCommand.Parameters.Clear(); 
                }
            }

        }

        public static void SavePerson(Person person)
        {            
            string query = "INSERT INTO Persons(FirstName,LastName,DOB) VALUES(@FirstName,@LastName,@DOB) SELECT SCOPE_IDENTITY()";

            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                SqlCommand myCommand = new SqlCommand(query, conn);
                myCommand.Parameters.AddWithValue("@FirstName", person.FirstName);
                myCommand.Parameters.AddWithValue("@LastName", person.LastName);
                myCommand.Parameters.AddWithValue("@DOB", person.DOB);
                conn.Open(); 
                person.Id = Convert.ToInt32(myCommand.ExecuteScalar());

                // save the addresses! 
                SaveAddress(person.Addresses); 
            }            
        }

        public static Person GetPersonById(int id)
        {
            /*
             * we used left outer join since we want to return the person object even if it does not have 
             * the corresponding address object!
             * */
            string query = @"SELECT p.PersonID,p.FirstName,p.LastName,p.DOB,a.street FROM Persons p 
                            left outer join addresses a on a.personid = p.personid
                            WHERE p.PersonID = @PersonID";

            Person person = new Person();

            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                SqlCommand myCommand = new SqlCommand(query, conn);
                myCommand.Parameters.AddWithValue("@PersonID", id);
                conn.Open();
                SqlDataReader reader = myCommand.ExecuteReader();
                while (reader.Read())
                {
                    person.Id = (int)reader["PersonID"]; 
                   person.FirstName = reader["FirstName"] as String; 
                   person.LastName = reader["LastName"] as String; 
                   person.DOB = Convert.ToDateTime(reader["DOB"]);
                   
                    // add the address to the person object! 
                    person.AddAddress(new Address(person) { Street = reader["Street"] as String });           
                 
                };                   
                              
            }

            return person; 
        }

    }
}