How do I configure navigation properties of varying multiplicity between two tables using fluent API

Question

I'm new to Entity Framework and I am trying to configure two navigation properties in a Code-First project.

The first property is a collection of employee_pay_period(s). Each employee_salary has multiple employee_pay_period(s) and each employee_pay_period has one employee_salary.

employee_pay_period.employee_salary_id is a foreign key.

The second property, employee_salary.employee_current_pay_period, is a bit more tricky. It is a property that points to the current employee_pay_period. So a navigation property going from one employee_salary to one employee_pay_period. There is NO foreign key in the DB associated with the second property and each employee_salary MUST contain an employee_current_pay_period.

How do I use fluent API to map these properties correctly.

public class employee_salary
{
    public employee_salary()
    {
        employee_pay_period = new HashSet<employee_pay_period>();
    }

    [Key]
    public int employee_salary_id { get; set; }

    public int? employee_current_pay_period_id { get; set; }

    public virtual employee_pay_period employee_current_pay_period { get; set; }

    public virtual ICollection<employee_pay_period> employee_pay_period { get; set; }

}



public partial class employee_pay_period
{

    [Key]
    public int employee_pay_period_id { get; set; }

    public int employee_salary_id { get; set; }

    public virtual employee_salary employee_salary { get; set; }
}

Answer 1

If I understand correctly you want a 1-many relationship between employee_salary and employee_pay_period respectively but also a 1-1 relationship between an employee_salary and the current employee_pay_period

So something like this (assuming you already have the rest of the fluentApi context configuration class set up) in the OnModelCreating(ModelBuilder builder) function:

builder.Entity<employee_salary>(e =>
{
    e.HasMany(s => s.employee_pay_period) // salary has many pay periods
        .WithOne(p => p.employee_salary) // pay period has one salary
        .HasForeignKey(p => p.employee_salary_id) // foreign key on pay period linking to a single salary id
        .OnDelete(DeleteBehavior.Restrict); // Or whatever the desired delete behaviour should be

    e.HasOne(s => s.employee_current_pay_period) // salary has one current pay period
        .WithOne(p => p.employee_salary) // pay period has one salary
        .HasForeignKey<employee_salary>(s => s.employee_current_pay_period_id) // foreign key on salary linking to a single current pay period id
        .OnDelete(DeleteBehavior.Restrict); // Or whatever the desired delete behaviour should be
}