OOP PHP - 通过函数传递方法[重复]

Question

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• Call to a member function on a non-object [duplicate] 8 answers

I am new to OOP in PHP and I am trying to understand how it work. I am trying to implement PDO into a my own class.

This is what I am doing:

class db {

    private $options;

    function __construct() {
        $this->options = array(
            'database_host' => DATABASE_HOST,
            'database_name' => DATABASE_NAME,
            'database_user' => DATABASE_USER,
            'database_pass' => DATABASE_PASS
        );

    }

    private function connect() {
        try {
            $pdo = new PDO('mysql:host=' . $this->options['database_host'] . ';dbname=' . $this->options['database_name'], $this->options['database_user'], $this->options['database_pass']);
            $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            $pdo->exec("set names utf8");
        } catch (PDOException $e) {
            echo 'ERROR: ' . $e->getMessage();
        }
    }

    public function select($table, $what, $where, $custom) {

        $query = "SELECT " . $what . " FROM " . $table;
        $child = "1";
        $param = array();
        if ($where)
            foreach ($where as $data => $value) {
                if ($child == "1") {
                    $query .= " WHERE " . $data . " = '" . $value . "'";
                    $param[":" . $data] = $value;
                    $child = "next";
                } else {
                    $query .= " AND " . $data . " = '" . $value . "'";
                    $param[":" . $data] = $value;
                }
            }

        if ($custom)
            $query .= ' ' . $custom;

        $statement = $pdo->prepare($query);
        if ($statement->execute($param))
            return $statement->fetchAll(PDO::FETCH_ASSOC);
        return false;
    }

}

The problem is that I don't know how to make the function connect() communicating with the below one select() When I try to call the select() function, I get this error:

Fatal error: Call to a member function prepare() on a non-object in /Applications/MAMP/htdocs/game/api/class.db.php on line 47

I would like that when I call the select() function, the connect() one connects to the DB and makes all its variables available for the other functions of the class...but I am lost.

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Answer 1

Store the $pdo variable as a property. Currently it is just a variable local to the connect() method.

class db {
    private $options;
    private $pdo;
}

Then use $this->pdo to access it from any of the methods. For example in your connect():

private function connect() {
    try {
        $this->pdo = new PDO('mysql:host=' . $this->options['database_host'] . ';dbname=' . $this->options['database_name'], $this->options['database_user'], $this->options['database_pass']);
        $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $this->pdo->exec("set names utf8");
    } catch (PDOException $e) {
        echo 'ERROR: ' . $e->getMessage();
    }
}

Do the same for your other methods, e.g.:

$statement = $this->pdo->prepare($query);

---

You might prefer to extend the PDO class, rather than having a new class that keeps a property of the PDO object. The difference is when extending it, your db class will behave the same as the PDO class, except it will have your additional methods available. Whereas with your current code, the db class only has methods that you explicitly define.