Catching specific exception

Question

How can I catch specific exception using c# ?
In my database there is unique index on some columns.
when user inserts duplicate record this exception has been throw :

Cannot insert duplicate key row in object 'dbo.BillIdentity' with unique index 'IX_BillIdentity'. The statement has been terminated.

How can I catch this exception?
Currently I am checking using this code :

 catch (Exception ex) {     if (ex.Message.Contains("Cannot insert duplicate key row in object 'dbo._BillIdentity' with unique index 'IX__BillIdentity")) {         string ScriptKey = "$(function() {ShowMessage('Error');});";         ScriptManager.RegisterStartupScript(Page, GetType(), "script", ScriptKey, true);     } } 

I think its bad smell code.
Is there any better way?

Answer 1

Handle SqlException only in this case.

[Edit]

To check duplicate key exception in MS SQL server:

try {     // try to insert } catch (SqlException exception) {     if (exception.Number == 2601) // Cannot insert duplicate key row in object error     {         // handle duplicate key error         return;                       }     else         throw; // throw exception if this exception is unexpected } 

Edit: Where 2601 come from?

select * from sys.messages where text like 'Cannot insert duplicate key%' 

Returns:

message_id  language_id severity is_event_logged text ----------- ----------- -------- --------------- ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 2601        1033        14       0               Cannot insert duplicate key row in object '%.*ls' with unique index '%.*ls'. The duplicate key value is %ls. 

Using exception.Number and referencing sys.messages view you can handle any specific MS SQL exception.

Answer 2

You haven't shown the type of exception which is thrown, but you can catch that specific exception type. For example:

catch (DuplicateKeyException e) {     ... } 

It's possible that there won't be a specific exception type for just this error - but if you have to catch something fairly general like SqlException you can then look for more details within the class itself. For example in SqlException there's an Errors property where you can look at more detailed information about each of the (possibly multiple) errors at the database side. Each SqlError then has a Number property which will give the type of error. You can always fall back to the message if you absolutely have to, but you then need to be aware of the possibility of the message changing for different cultures etc.

Note that if you're not really handling the exception, you should probably rethrow it:

catch (SqlException e) {     if (CheckWeCanHandle(e)) {         // Mess with the ScriptManager or whatever     } else {         throw;     } }