Oct 16 lecture notes

 1. Go over homework : see code/registrar_db/

 2. Perl/DBI : see code/registrar_db/queries.pl

 3. catching errors in perl:

    eval { ... code ... }
    
 4. transactions in SQL : committing and rolling back

 5. walk through perldoc DBI

 6. if time allows, 
    discuss packaging database stuff into a another file.
    Or continue this on Thursday

    (Review object oriented programming, modules, and all that.)

 7. Homework for Thurs:
    * Read about Perl/DBI; at least perldoc DBI
    * Review object oriented perl
    * Coming up : putting it all together...
    * After that: Class::DBI

    -- MyData.pm ---------------------
    
     package MyData;

     sub new {
        my $class = shift;
        my $dbh = DBI->connect(...);
	my $self = { dbh => $dbh };
	bless($self,$class);
	return $self;
     }

     sub set_data {
       # insert data into database
       my $self = shift;
       my ($arg1, $arg2) = @_;
       my $dbh->do(" ... sql goes here ... ", ...);
     }

     sub get_data {
       # get data from database
       my $self = shift;
       my $answer = '';
       my ($this, $that) = shift;
       eval {
         my $sth=$dbh->prepare(...);
	 $sth->execute(...);
	 $answer = $sth->fetch...
       }
       return $answer;
     }

     sub do_tests {
       # ... make sure all this stuff works...
     }

    --- myCGI.cgi (or Mason file) ------------------
    use CGI;
    use MyData;  # ***** All SQL is hidden in here. ****
    my $database = new MyData;
    
    my $from_user = ... # get stuff from form
    $database->set_data( $from_user ...);

    # or to get stuff from database

    my $stuff_from_db = $database->get_data( ... );

    # print HTML page, or whatever