Dynamic prepared statement, PHP - php

Question

I've checked almost all questions that produce the same error but all of these questions bind parameters in some wrong way. Perhaps and most probably I too am binding params incorrectly though my case is different because I've dynamic query.
I am creating query dynamically from input which is being created perfectly. But problem comes from $stmt->bind_param statement within foreach loop. Here is my Code snippet that is erronous:
$query = "UPDATE users SET";
foreach($updationFields as $field => $value){
if($value != "-"){
$query = $query. " " . $field . " = :".$field.",";
}
}
$query = rtrim($query, ",");
$query = $query . " WHERE UserId = :UserId";
$stmt = $this->conn->prepare($query);
foreach($updationFields as $field => $value){
echo $field;
if($value != "-"){
$input = ":".$field;
$stmt->bind_param($input, $value); // This line produces error
}
}
$stmt->bind_param(":UserId", $userId);
$stmt->execute();
Here is produced dynamic "string query" for one field:
UPDATE users SET fullName = :fullName WHERE UserId = :UserId
Error says: Fatal error: Call to a member function bind_param() on a non-object in
Any Idea what i am doing wrong?

Answer 1

As pointed out by #Fred-ii- and #commorrissey :Placeholder is supported by PDO not mysqli so so I had to:
Replace :Placeholders with ?
Call bind_param with call_user_func_array feeding dynamic references as expected by mysqli_stmt.
Here is the code that creates dynamic binding:
$params = array();//
$params[] = $type;
$i=0;
foreach($updationFields as $field => $value){
if($value != "-"){
$bind_name = 'bind' . $i;
$$bind_name = $value;
$params[] = &$$bind_name;
$i++;
}
}
$bind_name = 'bind' . $i;
$$bind_name = $userId;
$params[] = &$$bind_name;
$return = call_user_func_array(array($stmt,'bind_param'), $params);