Implementing if-not-exists-insert using Entity Framework without race conditions

Question

Using LINQ-to-Entities 4.0, is there a correct pattern or construct for safely implementing \"if not exists then insert\"?

For example, I currently have a table that tra

Answer 1

You can also write a stored procedure that uses some new tricks from sql 2005+

Use your combined unique ID (userID + articleID) in an update statement, then use the @@RowCount function to see if the row count > 0 if it's 1 (or more), the update has found a row matching your userID and ArticleID, if it's 0, then you're all clear to insert.

e.g.

Update tablex set userID = @UserID, ArticleID = @ArticleID (you could have more properties here, as long as the where holds a combined unique ID) where userID = @UserID and ArticleID = @ArticleID

if (@@RowCount = 0) Begin Insert Into tablex ... End

Best of all, it's all done in one call, so you don't have to first compare the data and then determine if you should insert. And of course it will stop any dulplicate inserts and won't throw any errors (gracefully?)

Answer 2

You could try to wrap it in a transaction combined with the 'famous' try/catch pattern:

using (var scope = new TransactionScope())
try
{
//...do your thing...
scope.Complete();
}
catch (UpdateException ex)
{
// here the second request ends up...
}