更新记录在LINQ to SQL中不起作用

Question

I have this sequence generation query that gets the current sequence and increment it to next value. But the increment is not updating. The nextval is always returning 1, the default value from the database

Entity  | StartVal | Increment | CurVal | NextVal
----------------------------------------------------
INVOICE |   0      |     1     |   0    |   1

The nextval should be 3, 5, 7 and so on

int nextVal = 0;
using (var db = new MedicStoreDataContext())
{
    DAL.LINQ.Sequence seq = (from sq in db.Sequences
                where sq.Entity == entity
                select sq).SingleOrDefault();

    if (seq != null)
    {
        nextVal = seq.NextVal.HasValue ? seq.NextVal.Value : 0;


        seq.NextVal = nextVal + 2;

        db.SubmitChanges();
    }

}

Have I left something undone?

UPDATE: Answer: I needed to set the Primary Key and update Sequence class field to include the Primary Key

Answer 1

Usually this is because it hasnt found the unique identifier (or Primary Key) for a table.

In your data descriptions are you sure the table correctly picked up the unique item? - when I first tried this although I had a unique key etc, the table description in c# didnt mark it as unique, so the linq quietly didnt updated it as I had expected, no errors no warnings. Once I corrected the data table in c#, it all went well.

Answer 2

Isn't that the correct behaviour? wouldn't you expect nextVal to be 1 if CurVal is 0? I may be missing something here but it seems like your overcomplicating it a bit. Isn't what you want to do basically

using (var db = new MedicStoreDataContext())
{
    DAL.LINQ.Sequence seq = (from sq in db.Sequences
                where sq.Entity == entity
                select sq).SingleOrDefault();

    if (seq != null)
    {
        seq.CurVal += seq.Increment;

        db.SubmitChanges();
    }
}

I don't see why you need the whole nextVal bit at all. Please feel free to correct me if I'm wrong.