Perl, SQL, DBI: Why doesn't my UPDATE function work? Code and things I've tried inside - mysql

Question

UPDATE 2: I never found the solution to this. Since the instructor's code is readily available for us to use and hack together with our own, and I'd already wasted weeks trying to debug, I just created a new table and started from his code, made changes and tested as I went, until I ended up with that I wanted in functionality. If anyone every comes across a reason for the odd behavior, I'd sincerely appreciate knowing what caused this.
Almost everyone who suggested anything offered up ideas I had already tried, and listed as already tried, in my original post. Thank you to everyone offering their insight, but please do read posts completely before making suggestions.
UPDATE: to present my main question more clearly. The original post is below that with all code, as well as what I've tried.
I designed my updateData() function to update a record. Instead, it returns its error code.
sub updateData {
# and this returns "Update Failed!" for me. I can't figure out why.
$sql = "UPDATE friendface SET first_name = '$first_name',
last_name = '$last_name',
email_address = '$email_address',
password = '$password'
WHERE user_id = $user_id;";
$rc = $dbh->do($sql);
if ($rc != 1) {
print "Update Failed!";
}
}
Ninja editing as I reread through this mess 3:
Code at the bottom. Sorry if the formatting is awful or I'm not descriptive enough. I really tried. Ask if I can provide anything else that is helpful.
Hi everyone,
School assignment here, print a table with records you can edit and delete.
I've got an HTML page with forms for inserting data, then a perl script that displays the table with buttons to update and delete. Delete works fine. The whole script works fine (EXCEPT the link from the block of text you get when you access the .pl directly, but I don't care about that at the moment) without the contents of my UPDATE function. The code for the UPDATE function works fine line by line in MySQL. But I can't get the updateData function with the UPDATE query to work in my .pl file.
We're allowed full access to the instructor's example code. I COULD start with his page, then modify it into my own page. I'd rather be able to write my own page without relying on that crutch. I am, however, comparing my code to his and I don't see where I'm going wrong. Syntax looks good, as far as I know / can find docs for.
I played with varying syntax anyway just in case. Put a comma after the final record before my WHERE clause because it looked wrong without, but apparently without is the way to go. Everything I read says the current syntax is correct.
I thought maybe it was trying to edit a user_id that didn't exist, but printing the user_id showed it was using the correct one.
I think my DBI->connect is working because it doesn't return Connection Failed.
The correct function, updateData(), is running because the final output is the Update Failed return code, unique to that function.
I can trace the code through Edit button > Edit form > Confirm Edit function > updateData function > $dbh authenticates successfully, do($sql), which is my UPDATE query, which looks syntactically correct. But for some reason, $dbh->do($sql); doesn't come out true.
In the updateData function, I thought I'd make sure the problem wasn't that I was only updating 4 of the 6 fields. Well, 5, since the key isn't ever going to be updated. Anyway, I thought that might be tripping it up somehow, but adding a line to update username didn't help, so I took it out again.
I've really been trying to figure this out on my own and I'm pulling my hair out. It's always some dumb little thing. Is it spacing? It usually doesn't matter, but I know ENDFORM had to be the first, and only, thing on the line in order to work for me. But I don't know of any spacing rules for this particular code. Please. Point me in the right direction.
Just to be explicit, printEditButton() and printDeleteButton() are the code for the edit and delete buttons...
DESC table, code for the html page, and the pl script follows:
*********************
*********************
***DESC friendface***
*********************
*********************
Field Type Null Key Default Extra
user_id int(11) NO PRI NULL auto_increment
username char(50) YES NULL
first_name char(20) YES NULL
last_name char(20) YES NULL
email_address char(50) YES NULL
password char(50) YES NULL
*********************
*********************
*friendFaceForm.html*
*********************
*********************
<table bgcolor='antiquewhite' align=center cellpadding=2>
<form action='friendFaceForm.pl' method=GET>
<tr>
<td align=right>Username</td>
<td><input type=text name=username></td>
</tr>
<tr>
<td align=right>First Name</td>
<td><input type=text name=first_name></td>
</tr>
<tr>
<td align=right>Last Name</td>
<td><input type=text name=last_name></td>
</tr>
<tr>
<td align=right>Email Address</td>
<td><input type=text name=email_address></td>
</tr>
<tr>
<td align=right>Password</td>
<td><input type=text name=password></td>
</tr>
<tr>
<td align=center colspan=2> <input type=submit name=action value='Insert Data'></td>
</tr>
</form>
</table>
*********************
*********************
**friendFaceForm.pl**
*********************
*********************
#!/usr/bin/perl
use CGI qw(:standard);
use DBI;
use warnings;
print "Content-type: text/html\n\n";
$dbh = DBI->connect("DBI:mysql:jwiard1:localhost", "jwiard1", "jwiard1")
or endProgram("Connection Failed!");
$action = param('action');
$user_id = param('user_id');
$username = param('username');
$first_name = param('first_name');
$last_name = param('last_name');
$email_address = param('email_address');
$password = param('password');
if ($action eq 'Insert Data') {
#$action holds this value coming from the html page
#this happens first
insertData();
printTable();
}
elsif ($action eq 'Edit') {
#prints the edit form
printEditForm();
}
elsif ($action eq 'Confirm Edit') {
#then updateData() runs
updateData();
printTable();
}
elsif ($action eq 'Delete') {
deleteData();
printTable();
}
elsif ($action eq 'Print Table') {
printTable();
}
else {
print "Either you are accessing this file directly or \$action has an unaccounted for value.<br><br>
If it's the former, get out of here!<br><br>
If it's the latter... you're getting sleepy. You're getting verrrry sleepy. When you reach the end of this sentence, you'll wake up with no memory of this page and a strong feeling that Joe Wiard's code is perfect.<br><br>
...or did you just want to see the table?";
print "<input type=submit name=action value='Print Table'>";
}
####
#Functions! Yay!
####
sub endProgram {
my ($msg) = #_;
print $msg;
die();
}
sub insertData {
#after inserting data, the user is left to click Edit or Delete
#making $action hold the value of 'Edit' or 'Delete' Go to elsif($action eq 'Edit'
print "Your data has been saved.";
$sql = "INSERT INTO friendface SET user_id='$user_id',
username='$username',
first_name='$first_name',
last_name='$last_name',
email_address='$email_address',
password='$password' ;";
$rc = $dbh->do($sql);
if ($rc != 1) {
print "Insert failed!";
}
}
sub printEditButton {
print "<form>";
print "<input type=hidden name=user_id value='$href->{user_id}'>";
print "<input type=submit name=action value='Edit'>";
print "</form>";
}
sub printDeleteButton {
print "<form>";
print "<input type=hidden name=user_id value='$href->{user_id}'>";
print "<input type=submit name=action value='Delete'>";
print "</form>";
}
sub confirmEdit {
}
sub lookUpRow {
$sql = "SELECT * FROM friendface WHERE user_id=$user_id;";
$sth = $dbh->prepare($sql);
$rc = $sth->execute();
$href = $sth->fetchrow_hashref();
}
sub printEditForm {
#prints fields for 4 of the values in a record. I don't want the user to be able to
#change their username. They can only edit first and last names, email and password.
#after this, $action either holds 'Confirm Edit' or 'Cancel'. Go to elsif
#($action'Confirm Edit')
lookUpRow();
print <<ENDOFFORM;
<form>
First Name: <input type=text name=first_name value='$href->{first_name}'> <br>
Last Name: <input type=text name=last_name value='$href->{last_name}'> <br>
Email Address: <input type=text name=email_address value='$href->{email_address}'> <br>
Password: <input type=text name=password value='$href->{password}'> <br>
<input type=hidden name=user_id value=$href->{user_id}'> <br>
<input type=submit value="Confirm Edit" name=action>
<input type=submit value="Cancel" name=action>
</form>
ENDOFFORM
#It seems that ENDOFFORM *MUST* be at the beginning of the line. No TABS or SPACES
#preceeding, and NOTHING after. Half an hour of debugging lead me to discovery this
#tidbit that I should have just remembered from class. Or Googled. :P
}
sub updateData {
#and this returns "Update Failed!" for me. I can't figure out why.
$sql = "UPDATE friendface SET first_name = '$first_name',
last_name = '$last_name',
email_address = '$email_address',
password = '$password'
WHERE user_id = $user_id ;";
$rc = $dbh->do($sql);
if ($rc != 1) {
print "Update Failed!";
}
}
sub deleteData {
$sql = "DELETE FROM friendface WHERE user_id = $user_id;";
$rc = $dbh->do($sql);
}
sub printTable {
$sql = "SELECT * FROM friendface;";
$sth = $dbh->prepare($sql);
$rc = $sth->execute();
$count = 0;
print "<table>";
#print header
while ($href = $sth->fetchrow_hashref() ) {
$count ++;
if ($count % 2 == 0) {
print "<tr bgcolor=lightblue>";
}
else {
print "<tr bgcolor=lightgray>";
}
print "<td>";
print $href->{'user_id'};
print "</td>";
print "<td>";
print $href->{'username'};
print "</td>";
print "<td>";
print $href->{'first_name'};
print "</td>";
print "<td>";
print $href->{'last_name'};
print "</td>";
print "<td>";
print $href->{'email_address'};
print "</td>";
print "<td>";
print $href->{'password'};
print "</td>";
print "<td>";
printEditButton();
print "</td>";
print "<td>";
printDeleteButton();
print "</td>";
print "</tr>";
}
print "</table>";

Answer 1

From the DBI documentation, it seems that the "do" method does some magic with the return value:
do
If you're doing an UPDATE, INSERT, or DELETE there is no data that
comes back from the database, so there is a short cut. You can say
$dbh->do('DELETE FROM people WHERE age > 65'); for example, and DBI
will prepare the statement, execute it, and finish it. do returns a
true value if it succeeded, and a false value if it failed. Actually,
if it succeeds it returns the number of affected rows. In the example
it would return the number of rows that were actually deleted. (DBI
plays a magic trick so that the value it turns is true even when it is
0. This is bizarre, because 0 is usually false in Perl. But it's convenient because you can use it either as a number or as a
true-or-false success code, and it works both ways.)
Are you sure the update didn't work? Perform a select afterward to double-check. It could just be that you're misinterpreting the return code.