linq2sql synchronized rapid udeletes

I'm having some timing problems in a unit test of some of my vb code.

I set up a test harness by checking for and then deleting records added to the db in the previous testing session, and then I test my recording adding code by adding back the same records.

Interestingly this code works fine when there is a break in the debugger, but fails with a "duplicate key" exception when I let it run with no breaks, which leads me to believe there is some kind of concurrency issue.

The basic metacode is as follows:

DoTest()  
  dim j as datacontext
  dim recs = from myrecs in j.mythings select myrecs where myrecs.key="key1" or  
  myrecs.key = "key2"
  if recs.count > 0
    for each rec in myrecs
      j.mythings.deleteonsubmit(rec)
    next
    j.submitchanges()
   end if
  j.dispose


  dim tc as new tablecontroller()  
  tc.addrecordtomytable("key1","value1")  
  tc.addrecordtomytable("key2","value2")  
end  

Class tablecontroller

Sub addrecordstomytable(key as string, value as string)
   dim j as new mydatacontext
   dim thing as new mything
   thing.key = key
   thing.value = value
   j.mythings.addonsubmit(thing)
   j.submitchanges
   j.dispose

end sub end class

I've confirmed that I'm properly deleted the previous added records, and this works 开发者_StackOverflowfine as does adding the new records when I have a break in the code before I hit the add records step. but without the break, it throws duplicate key exceptions in the "addrecordestomytable" method suggesting that it hasn't grabbed the current version of the table when it creates the new data context in addrecordstomytable, even though the records should have already been deleted.

I've tried refreshing the table, but this doesn't seem to work either.

Note backing database is ms sql server 10

Suggestions?

This is not so much an answer as a trouble-shooting technique. Have you tried using the log property? i.e.

j.log = Console.Out

So that you can see the actual SQL generated to make sure it is what you expect? Other than that is there anything relevant in your test setup or tear down? Is there anything managing a transaction? Are there triggers running? In terms of the latter if there is a trigger that takes some time to run and then the delete is finalized that might explain what you're seeing. I guess LINQ syntax varies between VB and C#, which surprised me, because I don't think your comparison code as written is valid in C#, you would need ==, not =, for a comparison but since it works when you break in the debugger...