Entity Framework Database Model

Question

Dear Entity experts and others,

I have the following entities,

Base class Individual:

 public abstract class Individual
    {
        [Key]
        public int IndividualID { get; set; }
        ... other properties
    }

Yogi:

 [Table("Yogis")]
    public class Yogi : Individual
    {
        public string Firstname { get; set; }
        public string Lastname { get; set; }
        public DateTime Birthdate { get; set; }
    }

Customer:

[Table("Customers")]
public class Customer : Individual
{
    public string Name { get; set; }

    [ForeignKey("VATID")] // tried with and without
    public virtual VAT VAT { get; set; }
}

VAT:

public class VAT
{
    [Key]
    public int VATID { get; set; }     

    [Required]
    public virtual Customer VATHolder { get; set; }
    ... other properties
}

DbContext:

  public DbSet<Individual> Individuals { get; set; }
  public DbSet<VAT> VATS { get; set; }

So the above creates a table VAT where there VATID is 2 to start with which should be 1 instead, I don't understand why this happens, this should be 1, isn't it? Also, there is no reference anywhere in any table that references Customer & VAT, how can I create a separate table VAT_Customer where you have a VATID & CustomerID ?

This is how i create and insert the entity Customer:

        VAT vat = new VAT("123456789");
        DataBaseHandler.InsertIndividual(new Customer("Customer name", vat,...));

Insert Function:

public static void InsertIndividual(Individual individual)
    {
        using (MyDbContext ctx = new MyDbContext())
        {               
                ctx.Individuals.Add(individual);    
                ctx.SaveChanges();                                    
        }
    }

I have tried several ways ( EXAMPLES HERE ) but I prefer the TPT way, having a separate view of any entity or relations between entities. What am I doing wrong and how would I achieve the desired result? Let me know if I can clarify anything. Thank you in advance for any help or suggestions!

Kind regards!

Answer 1

Your ForeignKey placement should look something like this if you wanna have 1:1 Relationship :

enter code here
[ForeignKey("VAT")] 
public virtual int VATId { get; set; }
public virtual VAT VAT { get; set; }

Name in the ForeignKey is same as your class.

hope this can help