PHP Fatal error: Call to a member function execute() on a non-object_问答_开发者

I get the error PHP Fatal error: Call to a member function execute() on a non-object refering to the ....->execute() line whenever I call something like

$select_str = 'select id, stamp, lat, lng, spd from gps';
$select = $db->prepare($select_str);
$select->execute();

$insert = $db->prepare('insert into gps (id, lat, lng, spd) values (?, ?, ?, ?)');
$insert->execute(array($id, $lat, $lng, $spd));

From searching on the net I suspect that $select (or $insert) is somehow becoming a "dead object" which holds the data, but on which methods can't be called.

But I don't know how to prevent it and my PHP experience is very short (I'm coming from Perl land). Please help me to fix this, it is probably something minor.

And below is my complete script, I think (I hope) it is quite readable - it lets you create a table, insert a record, delete records, view them or drop the table again - all depending on the $_REQUEST['mode'] parameter:

<?php

@define('DBHOST', 'localhost');
@define('DBNAME', 'snake');
@define('DBUSER', 'snake');
@define('DBPASS', 'snake');

# lowercase mode and id parameters; replace commas by dots in lat, lng, spd
$mode   = isset($_REQUEST['mode']) ? strtolower(trim($_REQUEST['mode']))     : '';
$id     = isset($_REQUEST['id'])   ? strtolower(trim($_REQUEST['id']))       : '';
$lat    = isset($_REQUEST['lat'])  ? strtr(trim($_REQUEST['lat']), ',', '.') : '';
$lng    = isset($_REQUEST['lng'])  ? strtr(trim($_REQUEST['lng']), ',', '.') : '';
$spd    = isset($_REQUEST['spd'])  ? strtr(trim($_REQUEST['spd']), ',', '.') : '';

# id must be 32 chars long hex number; lat, lng, spd must be decimal numbers
$id_ok  = preg_match('/^[a-f0-9]{32}$/', $id);
$lat_ok = preg_match('/^[+-]?[0-9.]+$/', $lat);
$lng_ok = preg_match('/^[+-]?[0-9.]+$/', $lng);
$spd_ok = preg_match('/^\+?[0-9.]+$/', $spd);

# has the user selected a mode and provided valid input?
$create_ok = ($mode == 'create');
$insert_ok = ($mode == 'insert' && $id_ok && $lat_ok && $lng_ok && $spd_ok);
$delete_ok = ($mode == 'delete' && $id_ok);
$select_ok = ($mode == 'select');
$drop_ok   = ($mode == 'drop');

# first call or invalid input: display web form and exit
if (!($create_ok || $insert_ok || $delete_ok || $select_ok || $drop_ok)) {
        header('Content-Type: text/html; charset=utf-8');
        print '<html>
<body>
<form method="post">
<p>Mode:<br />
<input type="radio" name="mode" value="create"><i>create table</i><br />
<input type="radio" name="mode" value="select" checked>select records (can specify id)<br />
<input type="radio" name="mode" value="insert">insert 1 record (must specify all)<br />
<input type="radio" name="mode" value="delete">delete records (must specify id)<br />
<input type="radio" name="mode" value="drop"><i>drop table</i><br />
</p>
<p>Id: <input type="text" name="id" size=32 maxlength=32 /> (32 hex chars)</p>
<p>Latitude: <input type="text" name="lat" size=10 /> (between -90 and 90)</p>
<p>Longitude: <input type="text" name="lng" size=10 /> (between -90 and 90)</p>
<p>Speed: <input type="text" name="spd" size=10 /> (not negative)</p>
<p><input type="submit" value="OK" /></p>
</form>
</body>
</html>
';
        exit();
}
try {
        # enable persistent connections and throw exception on any errors
        $options = array(PDO::ATTR_ERRMODE    => PDO::ERRMODE_EXCEPTION,
                         PDO::ATTR_PERSISTENT => true);
        $db = new PDO('mysql:host=' . DBHOST . '; dbname=' . DBNAME, DBUSER, DBPASS, $options);

        if ($create_ok) {
                $db->exec('create table gps (
                                id char(32) not null check length(id)=32,
                                lat decimal(5,3) not null,
                                lgt decimal(5,3) not null,
                                spd decimal(5,3) unsigned not null,
                                stamp timestamp default now(),
                                index(id) )');
        } else if ($insert_ok) {
        开发者_运维知识库        $insert = $db->prepare('insert into gps (id, lat, lng, spd) values (?, ?, ?, ?)');
                $insert->execute(array($id, $lat, $lng, $spd));
        } else if ($delete_ok) {
        } else if ($drop_ok) {
                $db->exec('drop table gps');
                header('Content-Type: text/plain');
                print('Database dropped');
                exit();
        }

        # display current table content in XML format
        $select_str = 'select id, stamp, lat, lng, spd from gps';
        # but filter by id if requested by user
        if ($select_ok && $id_ok) {
                $select = $db->prepare($select_str . ' where id = ?');
                $select->execute(array($id));
        } else {
                $select = $db->prepare($select_str);
                $select->execute();
        }

        header('Content-Type: text/xml; charset=utf-8');
        print('<?xml version="1.0"?><gps>');
        while ($row = $select->fetch(PDO::FETCH_ASSOC)) {
                printf('<pos id="%s" stamp="%u" lat="%f" lng="%f" spd="%f" />',
                    $row['id'], $row['stamp'], $row['lat'], $row['lng'], $row['spd']);
        }
        print('</gps>');
} catch (Exception $e) {
        header('Content-Type: text/plain');
        print('Database problem: ' . $e->getMessage());
}

?>

And the MySQL user 'snake' has these permissions:

select * from mysql.user where User='snake';
+-----------+-------+------------------+-------------+-------------+-------------+-------------+-------------+-----------+-------------+---------------+--------------+-----------+------------+-----------------+------------+------------+--------------+------------+-----------------------+------------------+--------------+-----------------+------------------+------------------+----------------+---------------------+--------------------+------------------+----------+------------+-------------+--------------+---------------+-------------+-----------------+----------------------+
| Host      | User  | Password         | Select_priv | Insert_priv | Update_priv | Delete_priv | Create_priv | Drop_priv | Reload_priv | Shutdown_priv | Process_priv | File_priv | Grant_priv | References_priv | Index_priv | Alter_priv | Show_db_priv | Super_priv | Create_tmp_table_priv | Lock_tables_priv | Execute_priv | Repl_slave_priv | Repl_client_priv | Create_view_priv | Show_view_priv | Create_routine_priv | Alter_routine_priv | Create_user_priv | ssl_type | ssl_cipher | x509_issuer | x509_subject | max_questions | max_updates | max_connections | max_user_connections |
+-----------+-------+------------------+-------------+-------------+-------------+-------------+-------------+-----------+-------------+---------------+--------------+-----------+------------+-----------------+------------+------------+--------------+------------+-----------------------+------------------+--------------+-----------------+------------------+------------------+----------------+---------------------+--------------------+------------------+----------+------------+-------------+--------------+---------------+-------------+-----------------+----------------------+
| localhost | snake | 684bce5059b3e0a8 | Y           | Y           | N           | Y           | Y           | Y         | N           | N             | N            | N         | N          | N               | Y          | N          | N            | N          | N                     | N                | N            | N               | N                | N                | N              | N                   | N                  | N                |          |            |             |              |             0 |           0 |               0 |                    0 |
+-----------+-------+------------------+-------------+-------------+-------------+-------------+-------------+-----------+-------------+---------------+--------------+-----------+------------+-----------------+------------+------------+--------------+------------+-----------------------+------------------+--------------+-----------------+------------------+------------------+----------------+---------------------+--------------------+------------------+----------+------------+-------------+--------------+---------------+-------------+-----------------+----------------------+

Thank you! Alex

The key is the behaviour of PDO::prepare():

If the database server successfully prepares the statement, PDO::prepare() returns a PDOStatement object. If the database server cannot successfully prepare the statement, PDO::prepare() returns FALSE or emits PDOException (depending on error handling).

prepare() is somehow failing with your query.

By default, PDO is mute and does not throw any error messages. See this page to see how to make PDO show errors, and details about what goes wrong.