Question

To represent our course tree structure in our Linq Dataclasses we have 2 columns that could potentially be the same as the PK.

My problem is that if I want to Insert a new record and populate 2 other columns with the PK that was generated there is no way I can get the next identity and stop conflict with other administrators who might be doing the same insert at the same time.

Case: A Leaf node has right_id and left_id = itself (prereq_id)

**dbo.pre_req:**
prereq_id
left_id
right_id
op_id
course_id
is_head
is_coreq
is_enforced
parent_course_id

and I basically want to do this:

        pre_req rec = new pre_req
        {
            left_id = prereq_id,
            right_id = prereq_id,
            op_id = 3,
            course_id = query.course_id,
            is_head = true,
            is_coreq = false,
            parent_course_id = curCourse.course_id
        };

        db.courses.InsertOnSubmit(rec);

        try
        {
            db.SubmitChanges();
        }

Any way to solve my dilemma? Thanks!

Answer 1

You don’t generate the Identity yourself, or directly set the ID values for FKs.

So, simplifying things down (because your structure isn’t terribly clear)

If your Person table looks like:

   Id  int IDENTITY(1,1)
   Name nvarchar(MAX)
   MotherId int NULL  (FK -> Person.Id)
   FatherId int NULL  (FK -> Person.Id)

Then your person Class in LINQ should look like:

public class Person 
{
   public int Id { get; set;}
   public string Name { get; set;} 
   public Person Mother { get; set;}
   public int? MotherId { get; set;}
   public Person Father { get; set;}
   public int? FatherId { get; set;}
}

When inserting, you can do this:

var mother = new Person { Name = "April Smith" }; 
var father = new Person { Name = "Bob Smith" }; 
var child = new Person { Name = "Charlie Smith", Mother = mother, Father = father}; 

db.People.InsertOnSubmit(mother);
db.People.InsertOnSubmit(father);
db.People.InsertOnSubmit(child); 

LINQ-to-SQL should then know to grab the generated Ids for mother and father, and insert them into the child record.

If you’re trying to self-referential or circular link, then there’s no way to do this in a single transaction that I know of.

You would have to insert your records first (and leave their references null initially) and then come back and update the references later.