Insert data simultaneously in entity having one to many relationship

Question

I have two entities: Student and Enrollement having a one-to-many relationship. The entities looks like

public class Student{
 [Key]
 public int Studentid {get; set;}
 public string fname{get; set;}
 public string lname{get; set;}
 public virtual ICollection<Enrollement> Enrollement_E{ get; set; }
 }

 public class Enrollement{
 [Key]
 public int EnrolId {get; set;}

 [ForeignKey("Studentid ")]
 public int Student{get; set;}
 public string kk{get; set;}
 public virtual Student Student_E { get; set; }
 }

Studentid is an autoincremented primary key and serve as foreign key in the enrollment table. I am trying to insert data into both table. Both inserts should not commit if either 1 fails. So, I have the following code.

try{
  repository.stu.insert(new student{fname = "fname", lname="lname"});
  repository.enr.insert(new Enrollement{student=???, kk="test"});
}
finally{
  repository.save();
}

How am I supposed to pass in the foreign key to the Enrollement record when the data has not been saved. Or is there another way of doing this?

Answer 1

Instead of assigning the foreign key, assign the whole object:

try{
  var student = new student(){fname = "fname", lname="lname"};
  repository.stu.insert(student);
  repository.enr.insert(new Enrollement(){Student_E = student});
}
finally{
  repository.save();
}

This way when student get's its new key it'll be autosaved into Enrollment.

Answer 2

You don’t need to save these two objects separately, You can achieve this by having on save call only

public class Student{
 [Key]
 public int Studentid {get; set;}
 public string fname{get; set;}
 public string lname{get; set;}
 public virtual ICollection<Enrollement> Enrollement_E{ get; set; }
 }

 public class Enrollement{
 [Key]
 public int EnrolId {get; set;}
 [ForeignKey("Studentid ")]
 public int Student{get; set;}
 public string kk{get; set;}
 public virtual Student Student_E { get; set; }
 }

Inside the connected OnModelCreating method , define the relation like, it will make sure when you have Student object, its related or child objects i.e Enrollements will also be saved

modelBuilder.Entity<Student>()
                .HasMany(c => c. Enrollement_E)
                .WithOne(e => e. Student_E);
modelBuilder.Entity<Enrollement>().Ignore(x => x. Student_E);

Now your code should look like this

try{
     student _student = new student{fname = "fname", lname="lname"};
     _student.Enrollement_E = new List< Enrollement>();
     _student.Enrollement_E.add(new Enrollement{student=???, kk="test"});
     repository.stu.insert(_student); 
}
finally
{
     repository.save();
}

This is done using Entity Framework Core one last thing, following conventions you also need to change the foreign Key field

public int Student{get; set;} to  public int StudentId{get; set;}

Answer 3

Ef easily handle foreign key to insert data to multiple related tables. if you want to insert your data simultaneously in two tables you can use below code for insert:

   student st = new student 
    {
      fname = "fname",
      lname= "lname",

      Enrollement_E=new List<Enrollement>
      {
        new Enrollement{kk="something"}
      }
    };

    repository.student.Add(st);
    repository.SaveChanges();

Ef itself makes foreign key for second table