Configure One-to-Many Relationship:

We are going to configure a One-to-Many relationship between Student and Standard, as many students are studying in one standard.

Configure One-to-Many relationship using DataAnnotation:

Student entity class has a reference property of Standard class with StandardId foreignKey property and Standard class has a collection property for Students. So this DataAnnotation will result in a One-to-Many relationship.

     
    public class Student
    {
        public Student() { }

        public int StudentId { get; set; }
        [Required]
        public string StudentName { get; set; }

         public int StdandardId { get; set; }
        
        public virtual Standard Standard { get; set; }
    }
        

    
    public class Standard
    {
        public Standard()
        {
            StudentsList = new List<Student>();
        }
        public int StandardId { get; set; }
        public string StandardName { get; set; }
        public string Description { get; set; }

        public virtual ICollection<Student> Students { get; set; }
    }
        

Configure One-to-Many relationship using Fluent API:

Suppose your Student and Standard entity class doesn't follow Code-First conventions and they have different property names, for example:

   
    public class Student
    {
        public Student(){ }

        public int StudentId { get; set; }
        [Required]
        public string StudentName { get; set; }

        //StdId is not following code first conventions name
        public int StdId { get; set; }

        public virtual Standard Standard { get; set; }
    }
        

    
    public class Standard
    {
        public Standard()
        {
            StudentsList = new List<Student>();
        }
        public int StandardId { get; set; }
        public string StandardName { get; set; }
        public string Description { get; set; }

        public virtual ICollection<Student> StudentsList { get; set; }
    }
        

So you can use Fluent API to configure a One-to-Many relationship between the Student and Standard entity classes:

    
   protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
            //one-to-many 
            modelBuilder.Entity<Student>().HasRequired<Standard>(s => s.Standard)
            .WithMany(s => s.StudentsList).HasForeignKey(s => s.StdId);

    }
        

Another possible way:

    
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
            //one-to-many
            modelBuilder.Entity<Standard>().HasMany<Student>(s => s.StudentsList)
            .WithRequired(s => s.Standard).HasForeignKey(s => s.StdId);
    }
        

The code shown above will create the following database:

The Entity Data Model in the designer will appear like the diagram shown below: