Entity Framework Configuring Relationships with the Fluent API

// Configure the primary key for the OfficeAssignment 
modelBuilder.Entity<OfficeAssignment>() 
    .HasKey(t => t.InstructorID); 
 
// Map one-to-zero or one relationship 
modelBuilder.Entity<OfficeAssignment>() 
    .HasRequired(t => t.Instructor) 
    .WithOptional(t => t.OfficeAssignment);

// Configure the primary key for the OfficeAssignment 
modelBuilder.Entity<OfficeAssignment>() 
    .HasKey(t => t.InstructorID); 
 
modelBuilder.Entity<Instructor>() 
    .HasRequired(t => t.OfficeAssignment) 
    .WithRequiredPrincipal(t => t.Instructor);

modelBuilder.Entity<Course>() 
    .HasMany(t => t.Instructors) 
    .WithMany(t => t.Courses)

modelBuilder.Entity<Course>() 
    .HasMany(t => t.Instructors) 
    .WithMany(t => t.Courses) 
    .Map(m => 
    { 
        m.ToTable("CourseInstructor"); 
        m.MapLeftKey("CourseID"); 
        m.MapRightKey("InstructorID"); 
    });

// Configure the primary Key for the OfficeAssignment 
modelBuilder.Entity<OfficeAssignment>() 
    .HasKey(t => t.InstructorID); 
 
modelBuilder.Entity<Instructor>() 
    .HasRequired(t => t.OfficeAssignment) 
    .WithRequiredPrincipal();

modelBuilder.Entity<Course>() 
    .HasRequired(t => t.Department) 
    .WithMany(t => t.Courses) 
    .HasForeignKey(d => d.DepartmentID) 
    .WillCascadeOnDelete(false);

// Composite primary key 
modelBuilder.Entity<Department>() 
.HasKey(d => new { d.DepartmentID, d.Name }); 
 
// Composite foreign key 
modelBuilder.Entity<Course>()  
    .HasRequired(c => c.Department)  
    .WithMany(d => d.Courses) 
    .HasForeignKey(d => new { d.DepartmentID, d.DepartmentName });

modelBuilder.Entity<Course>() 
    .HasRequired(c => c.Department) 
    .WithMany(t => t.Courses) 
    .Map(m => m.MapKey("ChangedDepartmentID"));

modelBuilder.Entity<Course>() 
         .HasRequired(c => c.Department) 
         .WithMany(d => d.Courses) 
         .HasForeignKey(c => c.SomeDepartmentID);

using System.Data.Entity; 
using System.Data.Entity.ModelConfiguration.Conventions; 
// add a reference to System.ComponentModel.DataAnnotations DLL 
using System.ComponentModel.DataAnnotations; 
using System.Collections.Generic; 
using System; 
 
public class SchoolEntities : DbContext 
{ 
    public DbSet<Course> Courses { get; set; } 
    public DbSet<Department> Departments { get; set; } 
    public DbSet<Instructor> Instructors { get; set; } 
    public DbSet<OfficeAssignment> OfficeAssignments { get; set; } 
 
    protected override void OnModelCreating(DbModelBuilder modelBuilder) 
    { 
        // Configure Code First to ignore PluralizingTableName convention 
        // If you keep this convention then the generated tables will have pluralized names. 
        modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); 
    } 
} 
 
public class Department 
{ 
    public Department() 
    { 
        this.Courses = new HashSet<Course>(); 
    } 
    // Primary key 
    public int DepartmentID { get; set; } 
    public string Name { get; set; } 
    public decimal Budget { get; set; } 
    public System.DateTime StartDate { get; set; } 
    public int? Administrator { get; set; } 
 
    // Navigation property 
    public virtual ICollection<Course> Courses { get; private set; } 
} 
 
public class Course 
{ 
    public Course() 
    { 
        this.Instructors = new HashSet<Instructor>(); 
    } 
    // Primary key 
    public int CourseID { get; set; } 
 
    public string Title { get; set; } 
    public int Credits { get; set; } 
 
    // Foreign key 
    public int DepartmentID { get; set; } 
 
    // Navigation properties 
    public virtual Department Department { get; set; } 
    public virtual ICollection<Instructor> Instructors { get; private set; } 
} 
 
public partial class OnlineCourse : Course 
{ 
    public string URL { get; set; } 
} 
 
public partial class OnsiteCourse : Course 
{ 
    public OnsiteCourse() 
    { 
        Details = new Details(); 
    } 
 
    public Details Details { get; set; } 
} 
 
public class Details 
{ 
    public System.DateTime Time { get; set; } 
    public string Location { get; set; } 
    public string Days { get; set; } 
} 
     
public class Instructor 
{ 
    public Instructor() 
    { 
        this.Courses = new List<Course>(); 
    } 
 
    // Primary key 
    public int InstructorID { get; set; } 
    public string LastName { get; set; } 
    public string FirstName { get; set; } 
    public System.DateTime HireDate { get; set; } 
 
    // Navigation properties 
    public virtual ICollection<Course> Courses { get; private set; } 
} 
 
public class OfficeAssignment 
{ 
    // Specifying InstructorID as a primary 
    [Key()] 
    public Int32 InstructorID { get; set; } 
 
    public string Location { get; set; } 
 
    // When the Entity Framework sees Timestamp attribute 
    // it configures ConcurrencyCheck and DatabaseGeneratedPattern=Computed. 
    [Timestamp] 
    public Byte[] Timestamp { get; set; } 
 
    // Navigation property 
    public virtual Instructor Instructor { get; set; } 
}