Question

If you please help me out I am trying to update a table with a unique constraint which is on all 4 keys (Role_ID, Track_ID, Person_ID, Conference_ID).

Why can I not update it?

error:

Description: An unhandled exception occurred during the execution of
the current web request. Please review the stack trace for more
information about the error and where it originated in the code.

Exception Details: System.Data.SqlClient.SqlException: Violation of
UNIQUE KEY constraint ‘UK_conferenceRole’. Cannot insert duplicate key
in object ‘dbo.ConferenceRole’. The statement has been terminated.

Code:

var sqlCon7 = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
string query7 = @"update ConferenceRole set Role_ID =" + 3 + ",Person_ID='" + idp + "'where Conference_ID ='" + conference + "'and Track_ID='" + TrackId + "'";

SqlCommand cmd7 = new SqlCommand(query7, sqlCon7);
cmd7.CommandType = CommandType.Text;

try
{
    sqlCon7.Open();
    cmd7.ExecuteNonQuery();
    sqlCon7.Close();
}
catch (Exception ee) 
{ 
    throw ee; 
}

Thanks in advance

Answer 1

Your code should look like this – by all means, avoid just stringing together your SQL statements! (that’s the door opener to SQL injection!). Also, with ADO.NET, you should put your connection and command into using-blocks to make sure they get properly disposed when no longer needed:

// define/read connection string and SQL statement
string connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
string sqlStatement = "UPDATE ConferenceRole SET Role_ID = @RoleID, " +
                      "Person_ID = @PersonID, " + 
                      "WHERE Conference_ID = @ConferenceID AND Track_ID = @TrackID";

// put your SqlConnection and SqlCommand into using blocks!
using(SqlConnection _con = new SqlConnection(connectionString))
using(SqlCommand _cmd = new SqlCommand(sqlStatement, _con))
{
   // define and set parameter values
   _cmd.Parameters.Add("@RoleID", SqlDbType.INT).Value = 3;
   _cmd.Parameters.Add("@PersonID", SqlDbType.INT).Value = idp;
   _cmd.Parameters.Add("@ConferenceID", SqlDbType.INT).Value = conference;
   _cmd.Parameters.Add("@TrackID", SqlDbType.INT).Value = trackId;

   // execute query 
   _con.Open();
   _cmd.ExecuteNonQuery();
   _con.Close();
}

And this construct here:

catch (Exception ee) 
{ 
    throw ee; 
}

is absolutely pointless – all it does is destroy the call stack, e.g. you won’t be able to see where the exception really came from anymore – just leave it out all together, or if you must – use

catch (Exception ee) 
{ 
    throw;   // **DO NOT** specify the 'ee' exception object here! 
}

What the error says it that you’re trying to create a duplicate entry into the table – one with a combination (Role_ID, Track_ID, Person_ID, Conference_ID) that already exists. That’s the whole point of the unique constraint: to prevent this from happening. So check your table – you must already have an entry in your table that has the same four values as the one you’re trying to update this row to….