php: variable scope within a class - php

Question

I am getting started with classes and have a variable scope question. I am defining a variable $query in one function and need to use it in a second function. However, the second function is not seeing it.
I guess I could pass $query to outside the class and then pass it along ($instance->QueryExecute($query);). But that seems messy, there is no need for $query to exist outside the class.
What is the correct way of solving this?
Thank you,
Louis.
<?php
class MyProduct {
public function QueryBuild() {
$query = "SELECT * FROM my_product";
}
public function QueryExecute() {
$result = mysql_query($query);
while ($record = mysql_fetch_assoc($result)) {
foreach ($record AS $key => $value) {
$this->product[$record["pro_id"]][$key] = $value;
}
}
}
}
?>

Answer 1

There are two options to solve your problem and the first is (in my opinion) better than the other:
Option 1: Return value
Just tell your build method to return the value and then use it on your other method:
<?php
class MyProduct {
public function QueryBuild() {
$query = "SELECT * FROM my_product";
return $query;
}
public function QueryExecute() {
$result = mysql_query($this->QueryBuild());
while ($record = mysql_fetch_assoc($result)) {
foreach ($record AS $key => $value) {
$this->product[$record["pro_id"]][$key] = $value;
}
}
}
}
Option 2: Object field
You define a field in your class that holds the query. This, however, means that the method QueryBuild() always has to be called before you can call QueryExecute(), which is not particularly reasonable.
<?php
class MyProduct {
private $query;
public function QueryBuild() {
$this->query = "SELECT * FROM my_product";
}
public function QueryExecute() {
$result = mysql_query($this->query);
while ($record = mysql_fetch_assoc($result)) {
foreach ($record AS $key => $value) {
$this->product[$record["pro_id"]][$key] = $value;
}
}
}
}
Some things to note:
Don't use mysql_* functions. They are deprecated and have been replaced with MySQLi and PDO.
Take a look at coding conventions. Method names should start with a small letter, which makes the code easier to read for everybody used to these standards.

Answer 2

You define a property in the class, that said I would like to add that mysql_* functions are deprecated.
<?php
class MyProduct {
private $query;
public function QueryBuild() {
$this->query= "SELECT * FROM my_product";
}
public function QueryExecute() {
$result = mysql_query($this->query);
while ($record = mysql_fetch_assoc($result)) {
foreach ($record AS $key => $value) {
$this->product[$record["pro_id"]][$key] = $value;
}
}
}
}
?>