Setting up multiple Foreign keys of same class in .Net Core / EF Core

Question

I'm building a .Net Core web app to replace an old legacy Access ADP/ADE front end to a project management SQL Server database. However, the builder of the original DB didn't setup a whole lot of Foreign key relationships in favor of doing it all in SQL views. Something I'm hoping to remedy with this app.

I'm wanting to make sure I have my head wrapped around setting up foreign keys when they are of the same class type. For example, I've got the following classes.

Project.cs

using System;
using System.Collections.Generic;

namespace ProjectLogic.Models
{
    public class Project
    {
        public int Id { get; set; };
        public string Name { get; set; }
        public int? PmEmployeeId { get; set; }
        public int? CadEmployeeId { get; set; }
        public int? SalesRepEmployeeId { get; set; }
        ...
    }
}

Employee.cs

using System;
using System.Collections.Generic;

namespace ProjectLogic.Models
{
    public class Employee
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Title { get; set; }
        ...
    }
}

Would my keys at the end of the Project Class look like this?

public Employee PmEmployee { get; set; }
public Employee CadEmployee { get; set; }
public Employee SalesRepEmployee { get; set; }

With corresponding declarations in Employee Class

public ICollection<Project> Projects { get; set; }

And the Model Builder in my DbContext class

modelBuilder.Entity<Project>(entity =>
{
// Fluent API for column properties
...
entity.HasOne(d => d.PmEmployee)
    .WithMany(p => p.Projects)
    .HasForeignKey(d => d.PmEmployeeId)
    .OnDelete(DeleteBehavior.SetNull)
    .HasConstraintName("FK_Project_Employee_PM");

entity.HasOne(d => d.CadEmployee)
    .WithMany(p => p.Projects)
    .HasForeignKey(d => d.CadEmployeeId)
    .OnDelete(DeleteBehavior.SetNull)
    .HasConstraintName("FK_Project_Employee_CAD");

entity.HasOne(d => d.SalesRepEmployee)
    .WithMany(p => p.Projects)
    .HasForeignKey(d => d.SalesRepEmployeeId)
    .OnDelete(DeleteBehavior.SetNull)
    .HasConstraintName("FK_Project_Employee_SALES");
});

I guess my biggest concern/question is how the Employee class will handle multiple relationships with the Project Class. Do I need to handle those separately as well like public ICollection<Project> PmProjects { get; set; }?

Answer 1

Yes, you need to have separate project collections.

In Employee, you would have:

public ICollection<Project> PmProjects { get; set; }
public ICollection<Project> CadProjects { get; set; }
public ICollection<Project> SalesProjects { get; set; }

In Project, you would have:

public Employee PmEmployee { get; set; }
public Employee CadEmployee { get; set; }
public Employee SalesRepEmployee { get; set; }

The builder would be :

modelBuilder.Entity<Project>(entity =>
{
// Fluent API for column properties
...
entity.HasOne(d => d.PmEmployee)
    .WithMany(p => p.PmProjects)
    .HasForeignKey(d => d.PmEmployeeId)
    .OnDelete(DeleteBehavior.SetNull)
    .HasConstraintName("FK_Project_Employee_PM");

entity.HasOne(d => d.CadEmployee)
    .WithMany(p => p.CadProjects)
    .HasForeignKey(d => d.CadEmployeeId)
    .OnDelete(DeleteBehavior.SetNull)
    .HasConstraintName("FK_Project_Employee_CAD");

 entity.HasOne(d => d.SalesRepEmployee)
    .WithMany(p => p.SalesProjects)
    .HasForeignKey(d => d.SalesRepEmployeeId)
    .OnDelete(DeleteBehavior.SetNull)
    .HasConstraintName("FK_Project_Employee_SALES");
 });