//CRUD + Link Existing-Records Operations
//CREATE
//https://www.codeproject.com/Tips/893609/CRUD-Many-to-Many-Entity-Framework
//Insert
private void Create(Student student, Course course)
{
using (var ctx = new M2MCollegeContext())
{
//Add instances to context
ctx.Students.Add(student);
ctx.Courses.Add(course);
//Add instance to navigation property
student.Courses.Add(course);
ctx.SaveChanges();
}
}
//DELETE RELATIONSHIP
//To delete relationship, instead of call Remove from context, we need to call it from
//navigation property.
private void DeleteRelationship(int studentId, int courseId)
{
using (M2MCollegeContext ctx = new M2MCollegeContext())
{
// Return one instance of each entity by primary key
var student = ctx.Students.FirstOrDefault(s => s.StudentId == studentId);
var course = ctx.Courses.FirstOrDefault(c => c.CourseId == courseId);
// Call Remove method from navigation property for any instance
// course.Students.Remove(student) also works
student.Courses.Remove(course);
ctx.SaveChanges();
}
}
private void SetupTestData()
{
using (M2MCollegeContext ctx = new M2MCollegeContext())
{
for (int i = 3; i < 8; i++)
{
string studentName = "Student" + i.ToString();
string courseName = "Course" + i.ToString();
var student = new Student {
StudentName = studentName
};
var course = new Course {
CourseName = courseName
};
Create(student, course);
}
}
}
//LINK
private void InsertWithData(int studentId, int courseId)
{
/*
* These steps apply to both entities
*
* 1 - create instance of entity with relative primary key
*
* 2 - add instance to context
*
* 3 - attach instance to context
*/
using (var ctx = new M2MCollegeContext())
{
//1
Student s = new Student
{
StudentId = studentId
};
//2
ctx.Students.Add(s);
//3
ctx.Students.Attach(s);
//1
Course c = new Course {
CourseId = courseId
};
//2
ctx.Courses.Add(c);
//3
ctx.Courses.Attach(c);
//Add instance to navigation property
s.Courses.Add(c);
ctx.SaveChanges();
}
}