Getting a basic PDO statement to execute - php

Question

I am attempting to get the following PDO statement to work and running into issues. When I am trying to get the number of rows, I keep getting 0, yet I know there should be 1 row. When I ran it as a mysqli statement( before trying to change it to PDO) it worked perfectly.
Here is the code:
require_once ('pdo.php');
$isbn = $_POST['isbn'];
// check to see if the isbn is a "problem" isbn or not
$problem = $conn->prepare("select isbn, note from problem where isbn = :isbn");
$problem->bindParam(":isbn", $isbn);
$problem->execute();
print_r($problem);
$num_rows = $problem->rowCount();
print_r($num_rows); die;
EDIT: Here is pdo.php:
<?php
function db_connect()
{
$db = new PDO("mysql:host=localhost; db=bookcell_BCOS_final", "xxxxx", "xxxxx");
return($db);
}
?>
I know that my connection works, but I get 0 for $num_rows. What mistakes am I making here?

Answer 1

Besides a little quirk and a optimalisation your code looks fine to me. The posted value isbn could be the reasong that you are getting no data:
$problem = $conn->prepare("select isbn, note from problem where isbn = :isbn");
$problem->bindParam(":isbn", $_POST['isbn'], PDO::PARAM_STR); // <-- thats what parameter binding is for
$problem->execute();
print_r($problem);
$num_rows = $problem->rowCount(); // <-- gives the number of rows, not columnCOunt
print_r($num_rows); die;

Answer 2

The Syntax for $num_rows = $problem->columnCount(); is totally correct. You may try,
$problem->execute(array("isbn" => $isbn));
instead of bindParam.

Answer 3

for getting the no. of rows, you need to use pdo::rowCount() -- manual here

Answer 4

In PDO to verfiy if your execute statement did work, check the return value (bool):
$success = $problem->execute();
if (!$success) {
$arr = $problem->errorInfo();
print_r($arr);
}
Also you might be looking for rowCount() instead of columnCount() but I think the error handling is your furthermost issue.
Additionally you can make PDO throw an exception each time an error appears, compare:
Switching from PHP's mysql extension to PDO. Extend class to reduce lines of code
How do I raise PDOException?

Answer 5

Depending on the database driver and the mode it's running, PDO may not be able to give you a row count. Look carefully at the documentation for PDOStatement::rowCount():
If the last SQL statement executed by the associated PDOStatement was a SELECT statement, some databases may return the number of rows returned by that statement. However, this behaviour is not guaranteed for all databases and should not be relied on for portable applications.
This is because in many cases the database uses a cursor rather than fetching the full results and buffering them (which is how the old mysql_* functions behave). In this case the database doesn't know how many rows there are until you have looked at all the rows. Think of a cursor as something like a filesystem pointer--you can't know the filesize until you seek to the end of the file.