opinion on preventing duplicate record insertion

Hi, i need an opinion on this...to prevent the duplicate record in db,i am using unique constraints for a column or combination of column as the case may be.By reading this articlehttp://aspalliance.com/687_Preventing_Duplicate_Record_Insertion_on_Page_Refresh.5 , i get the feeling that its not such a good idea..i am wondering,what does it imply?Does it mean that unique constraints are not reliable enough?Does it mean,it may break and let the duplicate record inserted,even though its not suppose to?I am using SQL server 2005

I have read Dino's article on dup recs and i have still not understood it completely.. i am looking for some not so complex ,full proof method,to prevent duplicate record insertion by clicking refresh or multiple (careless)clicking on submit...thanks ..

You essentially have two points of validation for the duplication.. at the code level, and at the database level.
You should employ both to good effect so that you do not get any and more importantly you control what happens when it already exists.

Unique constraints work - if you've set the correct ones, you will never get a duplicate entry in the database.
You should make sure you have them set.

Next, on a stored procedure that inserts the record, you can either try to insert and an error will occur because of the constraint and a SqlException will be generated that will bubble back to your code.
OR, you can use the IF EXISTS code that is suggested in the link you sent.
This checks if those valuse already exists in the database and doesn't try the insert.
I would advise that you also apply this to your logic.

On the code level, you can store Session or Viewstate Variables to flag that the update has happened as suggested in the fourth page of that article.

So you can incorporate all three so that

1. It checks the session variable and doesn't allow for duplicates
2. If it "slips the net" here, OR you later change your UI code, the stored procedure IF EXISTS catches and handles
3. If logic later changes, different sp used, your Unique Constraint will eventualy catch and throw an exception.

You are ensuing at all points that the problem cannot occur.

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"unique constraints" are reliable - the problem is handling the duplication condition. In my opinion the first method in the article is the preferred method - that of detecting the duplicate before the constraint does.