How to generate a uniqueidentifier in sql if null

Question

I am trying to add a column to an existing SQL table of uniqueidentifier type. That column must not be null and of course unique. I have attempted this code:

ALTER TABLE ScheduleJobs ADD CurrentInstanceID uniqueidentifier not null

followed by:

ALTER TABLE ScheduleJobs ADD CONSTRAINT DF_CurrentInstanceID DEFAULT newsequentialid() FOR CurrentInstanceID

However, when I create a new record (from C#), the uniqueidentifier is always all zeros (presumably null.) I can create the GUID in C# and pass it to sql upon creating a new record which works fine, but I am concerned that a duplicate GUID could be created. Based on my readings, it appears that would be an extremely rare case, but it always seems bad practice to have any sort of potential error floating around. Note that the field will not be a PK for the table. Suggestions and opinions welcome for the sake of education.

I am using C# 4.0 framework with MS SQL SERVER 2008

Answer 1

Sorry for the delay, but I am glad to say that I have this issue resolved. Thanks everyone for your overwhelming support. While no one quite hit the nail on the head (and there were some really good suggestions btw), Eldog brought up Entity Framework not playing nice in his comment. Thanks to him, I simply Googled Entity Framework + GUID and found the solution.

This article steps through the issue and gives a great explanation on the problem, solution, and steps to resolve it. I will note that I decided to step through and test one step at a time and that I didn't have to do the last step. That leads me to believe that part of the issue may have been resolved in later versions of the Entity Framework.

I simply pulled up the edmx file in design view (not xml) and set the StoreGeneratedPattern property to "Identity."

Thanks again for the help and suggestions. You're an awesome bunch.

Answer 2

Does your C# code attempt to pass in a CurrentInstanceID when creating the record? If so, can you drop that column from the INSERT statement?

We do this with numeric primary keys. Our C# code calls a stored procedure for CRUD operations on our records. The C# code generates a negative key on the client side for its own use. When it is ready to create the record, it passes this key to the stored procedure.

The proc ignores this key and inserts the rest of the data. The output of the proc is the actual key that SQL assigned to the record. Finally, the C# code merges the new key into the existing data.

Answer 3

I wouldn't use a GUID for this. GUIDs are used in quite a lot of operations in windows, so this won't be an identifier that will be only unique in your application , it will be a unique identifier in your operating system . Unless this makes sens in your case, I wouldn't use it.

You could use an incremental value, like a simple uint . If your table already has some data, you could write a script that fills existing rows with incremental values for your new column, and add the unique contraint to your column after executing that script.

Answer 4

in your original Create table or alter table use something like the following

create table ScheduleJobs (keyval int, id2 uniqueidentifier not null default newsequentialid())

then don't reference the column in your insert and a new GUID value will be added