如何从插入的数据中获取id

Hi guys im having difficulty on creating a logic on how to get an ID to an inserted data.My page has no userID or any. Just insertion of the data. I have two tables:

request to purchase table and ordered_items table. I separated the tables because i just need to store multiple data for items which hold an array of data.

heres my code:

<td><textarea name="item[]" value=""></textarea></td>
<td><textarea name="description[]" value=""></textarea></td>
<td><input type="text" name="qty[]" value="" /></td>
<td><input type="text" name="amount[]" value="" /></td>
<td><button class="add">Add</button></td>

and my methods are here:

public function insertRecord($param1, $param2, $param3, $param4) {

    $query = $this->db->prepare('INSERT INTO `request_to_purchase` (`requestedby`, `date`, `jobtitle`, `supervisor`, `notes`) VALUES (?, NOW(), ?, ?, ?)');

    $query->bindValue(1, $param1, PDO::PARAM_STR);
    $query->bindValue(2, $param2, PDO::PARAM_STR);
    $query->bindValue(3, $param3, PDO::PARAM_STR);
    $query->bindValue(4, $param4, PDO::PARAM_STR);

    try {

        $query->execute();

        $row = $query->rowCount();

        echo $row;

        if(count($row) > 0) {

            return true;
        } else {                
            return false;
        }

    } catch(PDOException $e) {

        die($e->getMessage());

    }

}

public function insertItem($arg1, $arg2, $arg3, $arg4, $arg5, $arg6) {

    $query = $this->db->prepare('INSERT INTO `ordered_item` (`rtp_id`, `item`, `description`, `qty`, `amount`, `date`) VALUES (?, ?, ?, ?, ?, ?)');

    $query->bindValue(1, $arg1);
    $query->bindValue(2, $arg2);
    $query->bindValue(3, $arg3);
    $query->bindValue(4, $arg4);
    $query->bindValue(5, $arg5);
    $query->bindValue(6, $arg6);
}

How do i get the rtp_id from request_to_purchase table so that i can insert it on the ordered item table. By then I can make a query Select * from ordered item table where rtp_id = ?

In PDO you can do like this:

$db->lastInsertId('yourIdColumn');

Docs Link: http://pt2.php.net/manual/en/pdo.lastinsertid.php

In your code snippet.

  if(count($row) > 0) {

        return $this->$db->lastInsertId();
    } else {                
        return false;
    }

Look at here Last Insert Id Already function available in PHP.

In your problem Use

$query->execute();
$last_inserted_id = $query->insert_id;

You can use

$id = mysql_insert_id();

Use this :

$db->lastInsertId();

For more info. see DOC

lastInsertId is a method of PDO, not PDOStatement