Delete Many to Many relationship using Entity Framework

Question

I've three tables Student (studID, fullName, gender...), Enroll (studID, courseID, date) and Course (courseID,courseName, ...). I used the code below to delete all records from Enroll table with studID 001 where there are about three courses the student signed for. However, it only deletes one record.

using(var context = new DBEntities())
{    
var _stud = (from s in context.Students where s.studID == "001" select s).FirstOrDefault();
                var _course = _stud.Courses.FirstOrDefault();
                _course.Students.Remove(_stud);
context.SaveChanges();
}

What do I miss here?

_course.Students.Load(); _course.Students.ToList().ForEach(s => context.Student.DeleteObject(s)); this should work. — Andrew
– Andrew, Commented Apr 11, 2014 at 13:49

Alexander Schmidt · Accepted Answer · 2016-12-19 11:45:06Z

5

Thank you guys for assisting. Here is how I solved it:

using (var context = new DBEntities())
{
    var student = (from s in context.Students where s.studID == "001" select s).FirstOrDefault<Student>();               
    foreach (Course c in student.Courses.ToList())
    {
        student.Courses.Remove(c);
    }
    context.SaveChanges();
}

edited Dec 19, 2016 at 11:45

Alexander Schmidt

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answered Apr 11, 2014 at 13:49

aby

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Comments

Andrew · Accepted Answer · 2014-04-11 13:47:05Z

0

I used the code below to delete all records from Enroll table

Are you deleting enrolls or students?

Student student = context.Student.FirstOrDefault(s => s.studID == "001");
if (student!=null)
{
    student.Enrolls.Load();
    student.Enrolls.ToList().ForEach(e => context.Enroll.DeleteObject(e));
}

edited Apr 11, 2014 at 13:47

answered Apr 11, 2014 at 13:39

Andrew

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Comments

Alexander Schmidt · Accepted Answer · 2016-12-19 11:47:53Z

0

Have you try this code :

var student = context.Students.Where(p => p.studID == "001").ToList();
foreach (var item in student)
{
    if (student != null)
    {
        var course = student.Courses.ToList();
        if (course != null)
        {
            foreach (var item2 in course)
            {         
                course.Students.Remove(item2);
                context.SaveChanges();
            }
        }           
   }
}

edited Dec 19, 2016 at 11:47

Alexander Schmidt

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answered Apr 11, 2014 at 12:42

Nayeem Mansoori

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1 Comment

aby Over a year ago

.Include(p => p.studID) produces error unless replaced by "Course." Even so, it only deletes one record (the top from the list)

Victor LG · Accepted Answer · 2018-08-20 23:09:56Z

0

For others looking to this answer you could also do it using include.

using(var context = new DBEntities())
{    
    // Get student by id
    var student = context.Students.Include(s => s.Courses).Where(s => s.studID == "001").FirstOrDefault();

    if(student.Courses != null)
    {
        // Retrieve list of courses for that student
        var coursesToRemove = stud.Courses.ToList();

        // Remove courses
        foreach (var course in coursesToRemove)
        {
            student.Courses.Remove(course);
        }

        // Save changes
        context.SaveChanges();
    }
}

answered Aug 20, 2018 at 23:09

Victor LG

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