CODEWITHSUNDEEP
.netentity-framework
Michael
Michael

Reputation: 13616

How to add new record in EF many-to-many relations?

I am working on my tutorial project I am new to entity framework.

I have many two many relationship tables I am using code first approach:

enter image description here

Here is tables definition:

 class EmployeeDBContext : DbContext
{
    public EmployeeDBContext() : base("DefaultConnection") { }
    public DbSet<Course> Courses { get; set; }
    public DbSet<Student> Students { get; set; }
}

//================================================My entities=================================================
public class Student
{
    [Key]
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public virtual ICollection<Course> Courses { get; set; }
}

public class Course
{

    [Key]
    public int CourseID { get; set; }
    public string CourseName { get; set; }
    public virtual ICollection<Student> Students { get; set; }
}

The course table filled with 3 subjects: History, Math, Physics.

I need to add new student and to relate the student to existing courses.

Any idea how can I implement it?

Upvotes: 4

Views: 141

Answers (2)

Muks
Muks

Reputation: 134

Try code below: Depends if you want to update the courseName or add student list. 

     public void UpdateCourse(string courseName, List<Student> students)
        {
            var dbInstance = new EmployeeDBContext();
            Course model = (from item in dbInstance.Courses
                            where item.CourseID = courseid
                            select item);
            model.CourseName = courseName;
            foreach(var item in  students)
              {     
               var currentStudent = from stud in dbInstance.Students
                       where stud.StudentId == item.StudentId;
               if( currentStudent != null) 
                 currentStudent.Name = item.Name; 
                else
                  dbInstance.Students.Add(new Student() {.StudentId = item.StudentId, .Name = item.Name});
            }; 
            dbInstance.SaveChanges(); 
        }


 public void CreateCourse(string courseName, List<Student> students)
    {
        var model = new Course();
        model.CourseName = courseName;
        model.Students = students;
        var dbInstance = new EmployeeDBContext();
        dbInstance.Courses.Add(model); 
        dbInstance.SaveChanges();
    }

Upvotes: 2

bubi
bubi

Reputation: 6491

If you need to create a student and add a course (or more courses) to him the way to do it with EF is the same as described with words...

using (var ctx= new EmployeeDBContext())
{
    // Create a new student (and set some properties)
    Student student = new Student()
    {
        StudentName = "Scott Tiger"
    };

    // Replace courseId with the course id that you need to add to the student
    student.Courses.Add(ctx.Courses.Find(courseId));
    // Add other courses if you need to

    // Let's write the student to the DB
    ctx.Students.Add(student);
    ctx.SaveChanges();

}

Upvotes: 2

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