Many-to-One Example (Shared address)

using Microsoft.EntityFrameworkCore;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace EFCore6Tests.MTO
{
    [Table("Client", Schema = "MTO")]
    public class Client
    {
        [Key]
        public int ClientId { get; protected set; }
        public string Name { get; set; }
        public virtual ClientAddress ClientAddress { get; set; }

#pragma warning disable CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
        public Client() { }
#pragma warning restore CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
    }

    [Table("Supplier", Schema = "MTO")]
    public class Supplier
    {
        [Key]
        public int SupplierId { get; protected set; }
        public string Name { get; set; }
        public virtual SupplierAddress SupplierAddress { get; set; }

#pragma warning disable CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
        public Supplier() { }
#pragma warning restore CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
    }

    [Table("Address", Schema = "MTO")]
    public class Address
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int AddressId { get; protected set; }
        public string Name { get; set; }
        public string? UnitNum { get; set; }
        public string StreetNum { get; set; }
        public string StreetName { get; set; }
        public string StreetType { get; set; }
        public int SuburbId { get; set; }
        //[ForeignKey(nameof(SuburbId)]
        //public Suburb Suburb { get; set; }
        public string City { get; set; }

#pragma warning disable CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
        public Address() { }
#pragma warning restore CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.

        public Address(string name, string? unitNum, string streetNum, string streetName, string streetType, int suburbId, string city)
        {
            Name = name;
            UnitNum = unitNum;
            StreetNum = streetNum;
            StreetName = streetName;
            StreetType = streetType;
            SuburbId = suburbId;
            City = city;
        }
    }

    [Table("ClientAddress", Schema = "MTO")]
    public class ClientAddress : IAddress
    {
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int ClientAddressId { get; protected set; }

        public virtual Address Address { get; set; } = new();
        public virtual Client? Client { get; set; }

        int IAddress.Id { get => ClientAddressId; }

        string IAddress.AddressType
        {
            get => typeof(ClientAddress).Name;
        }

        string IAddress.Name => Address.Name;

        string? IAddress.UnitNum => Address.UnitNum;

        string IAddress.StreetNum => Address.StreetNum;

        string IAddress.StreetName => Address.StreetName;

        string IAddress.StreetType => Address.StreetType;

        int IAddress.SuburbId => Address.SuburbId;

        string IAddress.City => Address.City;

        //public string Name { get => Address.Name; set => Address.Name = value; }

        //public string? UnitNum { get => Address.UnitNum; set => Address.UnitNum = value; }

        //public string StreetNum { get => Address.StreetNum; set => Address.StreetNum = value; }

        //public string StreetName { get => Address.StreetName; set => Address.StreetName = value; }

        //public string StreetType { get => Address.StreetType; set => Address.StreetType = value; }

        //public int SuburbId { get => Address.SuburbId; set => Address.SuburbId = value; }

        //public string City { get => Address.City; set => Address.City = value; }
    }

    [Table("SupplierAddress", Schema = "MTO")]
    public class SupplierAddress : IAddress
    {
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int SupplierAddressId { get; protected set; }

        public virtual Address Address { get; set; } = new();
        public virtual Supplier? Supplier { get; set; }

        int IAddress.Id { get => SupplierAddressId; }

        string IAddress.AddressType
        {
            get => typeof(SupplierAddress).Name;
        }

        string IAddress.Name => Address.Name;

        string? IAddress.UnitNum => Address.UnitNum;

        string IAddress.StreetNum => Address.StreetNum;

        string IAddress.StreetName => Address.StreetName;

        string IAddress.StreetType => Address.StreetType;

        int IAddress.SuburbId => Address.SuburbId;

        string IAddress.City => Address.City;
    }

    public interface IAddress
    {
        public int Id { get; }
        string AddressType { get; }

        string Name { get; }
        string? UnitNum { get; }
        string StreetNum { get; }
        string StreetName { get; }
        string StreetType { get; }
        int SuburbId { get; }
        string City { get; }
    }

    public class MTODbContext : DbContext
    {
        public DbSet<Client> Clients { get; set; }
        public DbSet<Supplier> Suppliers { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(@"Data Source=Machine\SQLEXPRESS;Initial Catalog=Inheritance;Trusted_Connection=Yes;MultipleActiveResultSets=True;TrustServerCertificate=True");
            base.OnConfiguring(optionsBuilder);
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);

            modelBuilder.Entity<Client>()
                .HasOne(x => x.ClientAddress)
                .WithOne(x => x.Client)
                .HasForeignKey<Client>("ClientAddressId");

            modelBuilder.Entity<Supplier>()
                .HasOne(x => x.SupplierAddress)
                .WithOne(x => x.Supplier)
                .HasForeignKey<Supplier>("SupplierAddressId");

        }
    }
}

using EFCore6Tests.MTO;
using Microsoft.EntityFrameworkCore;
using NUnit.Framework;

namespace EFCore6Tests
{
    [TestFixture]
    public class MTOTests
    {
        [Test]
        public void CreateTest()
        {
            using var context = new MTODbContext();

            var client = new Client
            {
                Name = "Test1",
                ClientAddress = new ClientAddress { Address = new MTO.Address { Name = "Test", StreetNum = "1a", StreetName = "Pelican", SuburbId = 2, StreetType = "Drive", City = "Bay City" } }
            };

            context.Clients.Add(client);
            context.SaveChanges();
        }

        [Test]
        public void ReadTest()
        {
            using var context = new MTODbContext();
            var clients = context.Clients.Include(x => x.ClientAddress).ToList();
        }

        [Test]
        public void AssociateAddressToSupplier()
        {
            using var context = new MTODbContext();
            var client = context.Clients.Include(x => x.ClientAddress).ThenInclude(x => x.Address).First();

            var supplier = new Supplier
            {
                Name = "Test",
                SupplierAddress = new SupplierAddress
                {
                    Address = client.ClientAddress.Address,
                }
            };

            context.Suppliers.Add(supplier);
            context.SaveChanges();

        }
    }
}