使用或处置 SqlConnection 不起作用，但 Close 可以吗？

Question

I have read the numerous posts on why you should give the using statement preference over manually doing .Open() then .Close() and finally .Dispose() .

When I initially wrote my code, I had something like this:

private static void doIt(string strConnectionString, string strUsername)
{
    SqlConnection conn = new SqlConnection(strConnectionString);
    try
    {
        conn.Open();
        string strSqlCommandText = $"CREATE USER {strUsername} for LOGIN {strUsername} WITH DEFAULT SCHEMA = [dbo];";
        SqlCommand sqlCommand = new SqlCommand(strSqlCommandText, conn);
        var sqlNonReader = sqlCommand.ExecuteNonQuery();
        if (sqlNonReader == -1) Utility.Notify($"User Added: {strUsername}");
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Error: {ex.Message}");
    }
    finally
    {
        conn.Close();
        conn.Dispose();
    }
}

and this works... no problem. but only ONCE.

so, if I do something like this:

private static void doItLots(string strConnectionString, string strUsername)
{
    for(int i=0; i<10; i++)
    {
        doIt(strConnectionString, $"{strUsername}_{i}");
    }
}

it works the FIRST time when i=0 , but any subsequent iterations fail with Cannot open database "myDbName" requested by the login. The login failed. Cannot open database "myDbName" requested by the login. The login failed.

However, if I go back and comment out the conn.Dispose(); line, then it works fine on all iterations.

The problem is simply that if I want to do the .Dispose() part outside of the method, then I am forced to pass a SqlConnection object instead of simply passing the credentials, potentially making my code a bit less portable and then I need to keep the connection around longer as well. I was always under the impression that you want to open and close connections quickly but clearly I'm misunderstanding the way the .Dispose() command works.

As I stated at the outset, I also tried doing this with using like this...

private static void doIt(string strConnectionString, string strUsername)
{
    using (SqlConnection conn = new SqlConnection(strConnectionString))
    {
        try
        {
            conn.Open();
            string strSqlCommandText = $"CREATE USER {strUsername} for LOGIN {strUsername} WITH DEFAULT SCHEMA = [dbo];";
            SqlCommand sqlCommand = new SqlCommand(strSqlCommandText, conn);
            var sqlNonReader = sqlCommand.ExecuteNonQuery();
            if (sqlNonReader == -1) Utility.Notify($"User Added: {strUsername}");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
        }
        finally
        {
            conn.Close();
        }
    }
}

and this does the exact same thing as the initial code with .Dispose() called manually.

Any help here would be greatly appreciated. I'd love to convert to the using statements but having trouble figuring out how to write reusable methods that way...

UPDATE:

I have narrowed it down a bit. The issue is NOT the iterations or making the calls over-and-over again. But I am still getting an access error. Here is the code:

        string strConnectionString = $@"Data Source={StrSqlServerDataSource};Initial Catalog={StrDatabaseName};User id={StrSqlServerMasterUser};Password={StrSqlServerMasterPassword}";

        using (SqlConnection connUserDb = new SqlConnection(strConnectionString))
        {
            try
            {
                Utility.Notify($"Connection State: {connUserDb.State.ToString()}"); // Responds as 'Closed'
                connUserDb.Open(); // <-- throws error
                Utility.Notify($"Connection State: {connUserDb.State.ToString()}");

                Utility.Notify($"MSSQL Connection Open... Adding User '{strUsername}' to Database: '{strDatabaseName}'");

                string sqlCommandText =
                    //$@"USE {StrDatabaseName}; " +
                    $@"CREATE USER [{strUsername}] FOR LOGIN [{strUsername}] WITH DEFAULT_SCHEMA = [dbo]; " +
                    $@"ALTER ROLE [db_datareader] ADD MEMBER [{strUsername}]; " +
                    $@"ALTER ROLE [db_datawriter] ADD MEMBER [{strUsername}]; " +
                    $@"ALTER ROLE [db_ddladmin] ADD MEMBER [{strUsername}]; ";
                using (SqlCommand sqlCommand = new SqlCommand(sqlCommandText, connUserDb))
                {
                    var sqlNonReader = sqlCommand.ExecuteNonQuery();
                    if (sqlNonReader == -1) Utility.Notify($"User Added: {strUsername} ({sqlNonReader})");
                }

                result = true;
            }
            catch (Exception ex)
            {
                Utility.Notify($"Creating User and Updating Roles Failed: {ex.Message}", Priority.High);
            }
            finally
            {
                connUserDb.Close();
                Utility.Notify($"MSSQL Connection Closed");
            }
        }
        return result;
    }

The error I am getting here is: Cannot open database requested by the login. The login failed. Cannot open database requested by the login. The login failed.

One clue I have is that prior to this, I was running this same code with two changes:

1) uncommented the USE statement in the sqlCommandText 2) connected to the Master database instead

When I did that, it didn't work either, and instead I got this error: The server principal is not able to access the database under the current security context.

If I go into SSMS and review the MasterUser they are listed as db_owner and I can perform any activities I want, including running the command included in the code above.

I rewrote all the code to make use of a single connection per the recommendations here. After running into the "server principal" error, I added one more connection to attempt to directly connect to this database rather than the master .

UPDATE 2:

Here is another plot twist...

This is working from my local computer fine (now). But, not (always) working when run from an Azure Webjob that targets an Amazon Web Services (AWS) Relational Database Server (RDS) running MSSQL.

I will have to audit the git commits tomorrow, but as of 5p today, it was working on BOTH local and Azure. After the last update, I was able to test local and get it to work, but when run on Azure Webjob it failed as outlined above.

Answer 1

SqlConnection implements IDisposable. You don't call dispose or close.

try{
 using (SqlConnection conn = new SqlConnection(strConnectionString))
    {

            conn.Open();
            string strSqlCommandText = $"CREATE USER {strUsername} for LOGIN {strUsername} WITH DEFAULT SCHEMA = [dbo];";
            SqlCommand sqlCommand = new SqlCommand(strSqlCommandText, conn);
            var sqlNonReader = sqlCommand.ExecuteNonQuery();
            if (sqlNonReader == -1) Utility.Notify($"User Added: {strUsername}");

    }}
catch (Exception ex)
            {
                Console.WriteLine($"Error: {ex.Message}");
            }