将MySQL链接传递给类方法

Here is my problem, i have a class with a ave method, i want to pass a Mysql DB link to it, so i create a new object from the class, and call the saveProperty method, and in my main file i created a MySQL connection and saved the link in a var called $db so when i call the method it's link this: saveProperty($db).Here is my problem, i have a class with a ave m