PDO update statement problems - php

Question

I am converting from mysqli to PDO and very much a beginner with this. Here is my update statement for my database 'users'
public function pdo_update_test() {
$sql = "UPDATE users SET visible_password = ?, hashed_password = ?, ";
$sql .="temp_hashed_password = ?, email = ?, first_name= ?, last_name = ?, ";
$sql .="position = ?, location = ?, city = ?, country = ?, institution = ? ";
$sql .="interests = ?, profile_comment = ? WHERE id =" . $this->id;
$query = $handler->prepare($sql);
$result = array($visible_password, $hashed_password, $temp_hashed_password, $email,
$first_name, $last_name, $position, $location, $city, $country, $institution,
$interests, $profile_comment);
$query->execute($result);
if (($query = $handler->prepare($sql)) === false) {
print_r($handler->errorInfo());
}
if ($query->execute($result) === false) {
print_r($query->errorInfo());
}
}
I am using ? rather than nameholders because once I have this working I am going to try to make it abstract so I can use it in all the classes in my site and I have found it easier with ? than nameholders. When I run the following it fails to work. I am sure an obvious error on my part but I can't seem to see the issue....
$user = new User();
$user->id= 256;
$visible_password = "Bob";
$user->pdo_update_test();
I have found a solution to make the whole thing dynamic. I won't presume that its going to be helpful for others (as I am the beginner) but i though I would post it anyway....
If you see problems or have criticisms please let me know
public function pdo_update_test(){
$attributes = $this->attributes();
$attribute_pairs = array();
foreach($attributes as $key => $value) {
if(isset($value))
$attribute_pairs[] = "{$key}='{$value}'";
}
$sql = "UPDATE ".self::$table_name." SET ";
$sql .= join(", ", $attribute_pairs);
$sql .= " WHERE id=". $this->id;
$query = $handler->prepare($sql);
$query->execute(array());
}

Answer 1

What you need is to create SET statement for the query dynamically. To make it contain only actual fields you have values for.
So, for the code given, it should produce a query
UPDATE users SET visible_password = ? WHERE id = ?
-- but not one you wrote above with all the fields listed
and it is not PDO related problem - it's rather just basic string manipulation, every PHP user is supposed to be able to write. If you can't, you can refer to PDO tag wiki for the code to adopt.
To make it work your code have to be like this
$user = new User();
$user->id= 256;
$data = array('visible_password' => "Bob");
$user->pdo_update_test($data);
where pdo_update_test will create the above SQL query out of $data array