PHP Data Objects

PHP Data Objects
Wez Furlong
<wez@messagesystems.com>

About me
• PHP Core Developer since 2001

• Author of the Streams layer

• I hold the title “King” of PECL

• Author of most of PDO and its drivers

What is PDO?
• PHP Data Objects

• A set of PHP extensions that provide a core PDO class and database
specific drivers

• Focus on data access abstraction rather than database abstraction

What can it do?
• Prepare/execute, bound parameters

• Transactions

• LOBS

• SQLSTATE standard error codes, flexible error handling

• Portability attributes to smooth over database specific nuances

What databases are supported?
• MySQL, PostgreSQL

• ODBC, DB2, OCI

• SQLite

• Sybase/FreeTDS/MSSQL

Connecting
try {

$dbh = new PDO($dsn, $user,
$password, $options);

} catch (PDOException $e) {

die(“Failed to connect:” .
$e->getMessage();

}

DSNs
• mysql:host=name;dbname=dbname

• pgsql:host=name dbname=dbname

• odbc:odbc_dsn

• oci:dbname=dbname;charset=charset

• sqlite:/path/to/file

Connection Management
try {

$dbh = new PDO($dsn, $user, $pw);
// use the database here
// ...
// done; release
$dbh = null;


die($e->getMessage();

}

DSN Aliasing
• uri:uri

• Specify location of a file that contains the actual DSN on the first
line

• Works with the streams interface, so remote URLs can work too
(this has performance implications)

• name (with no colon)

• Maps to pdo.dsn.name in your php.ini

• pdo.dsn.name=sqlite:/path/to/name.db

DSN Aliasing
pdo.dsn.name=sqlite:/path/to/name.db

$dbh = new PDO(“name”);

is equivalent to:

$dbh = new PDO(“sqlite:path/to/name.db”);

Persistent Connections
// Connection stays alive between requests

$dbh = new PDO($dsn, $user, $pass,
array(
PDO::ATTR_PERSISTENT => true
)
);

Persistent Connections
// Specify your own cache key

$dbh = new PDO($dsn, $user, $pass,
array(
PDO::ATTR_PERSISTENT => “my-key”
)
);

Useful for keeping separate persistent connections

Persistent PDO
The ODBC driver runs with connection pooling enabled
by default.

“better” than PHP-level persistence

Pool is shared at the process level

Can be forced off by setting:

pdo_odbc.connection_pooling=off

(requires that your web server be restarted)

Error Handling
• Maps error codes to ANSI SQLSTATE (5 character text string)

• also provides the native db error information

• Three error handling strategies

• silent (default)

• warning

• exception

PDO::ERRMODE_SILENT
// The default mode

if (!dbh->query($sql)) {
echo $dbh->errorCode(), “<br>”;
$info = $dbh->errorInfo();
// $info[0] == $dbh->errorCode()
// SQLSTATE error code
// $info[1] is driver specific err code
// $info[2] is driver specific
// error message
}

PDO::ERRMODE_WARNING
$dbh->setAttribute(PDO::ATTR_ERRMODE,
PDO::ERRMODE_WARNING);

Behaves the same as silent mode

Raises an E_WARNING as errors are detected

Can suppress with @ operator as usual

PDO::ERRMODE_EXCEPTION
$dbh->setAttribute(PDO::ATTR_ERRMODE,
PDO::ERRMODE_EXCEPTION);
try {
$dbh->exec($sql);
// display warning message
print $e->getMessage();
$info = $e->errorInfo;
// $info[0] == $e->code
// SQLSTATE error code
// $info[1] driver specific error code
// $info[2] driver specific error string
}

Get data
$dbh = new PDO($dsn);
$stmt = $dbh->prepare(
“SELECT * FROM FOO”);
$stmt->execute();
while ($row = $stmt->fetch()) {
print_r($row);
}
$stmt = null;

Forward-only cursors
• a.k.a. “unbuffered” queries in mysql parlance

• They are the default cursor type

• rowCount() doesn’t have meaning

• FAST!

Forward-only cursors
• Other queries are likely to block

• You must fetch all remaining data before launching another query

• $stmt->closeCursor();

Buffered Queries
$stmt = $dbh->query(“SELECT * FROM FOO”);
$rows = $stmt->fetchAll();
$count = count($rows);
foreach ($rows as $row) {
print_r($row);
}

Data typing
• Very loose

• Prefers strings

• Gives you more control over data conversion

Fetch modes

• $stmt->fetch(PDO::FETCH_BOTH);
- Array with numeric and string keys

- default option

• PDO::FETCH_NUM
- numeric keys only

• PDO::FETCH_ASSOC
- string keys only

Fetch modes

• PDO::FETCH_OBJ
- stdClass object

- $obj->name == ‘name’ column

• PDO::FETCH_CLASS
- You choose the class

• PDO::FETCH_INTO
- You provide the object

Fetch modes
• PDO::FETCH_COLUMN
- Fetches a column (example later)
• PDO::FETCH_BOUND
- Only fetches into bound variables
• PDO::FETCH_FUNC
- Returns the result filtered through a callback
• see the manual for more

Iterators
$stmt = $dbh->query(
“SELECT name FROM FOO”,
PDO::FETCH_COLUMN, 0);
foreach ($stmt as $name) {
echo “Name: $namen”;
}

$stmt = null;

Changing data
$deleted = $dbh->exec(
“DELETE FROM FOO WHERE 1”);

$changes = $dbh->exec(
“UPDATE FOO SET active=1 ”
.“WHERE NAME LIKE ‘%joe%’”);

Autonumber/sequences
$dbh->exec(
“insert into foo values (...)”);
echo $dbh->lastInsertId();

$dbh->exec(
“insert into foo values (...)”);
echo $dbh->lastInsertId(“seqname”);

Its up to you to call the right one for your db!

Prepared Statements
// No need to manually quote data here

“INSERT INTO CREDITS (extension, name)”
.“VALUES (:extension, :name)”);

$stmt->execute(array(
‘extension’ => ‘xdebug’,
‘name’ => ‘Derick Rethans’
));

Prepared Statements
// No need to manually quote data here

“INSERT INTO CREDITS (extension, name)”
.“VALUES (?, ?)”);

$stmt->execute(array(
‘xdebug’,
‘Derick Rethans’
));

$db->quote()

• If you really must quote things “by-hand”
• $db->quote() adds quotes and proper escaping as
needed
• But doesn’t do anything in the ODBC driver!
• Best to use prepared statements

Transactions
$dbh->beginTransaction();
try {
$dbh->query(“UPDATE ...”);
$dbh->query(“UPDATE ...”);
$dbh->commit();
$dbh->rollBack();
}

Stored Procedures
“CALL sp_set_string(?)”);
$stmt->execute(array(‘foo’));

“CALL sp_set_string(?)”);

$stmt->bindValue(1, ‘foo’);
$stmt->execute();

OUT parameters
“CALL sp_get_string(?)”);
$stmt->bindParam(1, $ret, PDO::PARAM_STR,
4000);
if ($stmt->execute()) {
echo “Got $retn”;
}

IN/OUT parameters
“call @sp_inout(?)”);
$val = “My input data”;
$stmt->bindParam(1, $val,
PDO::PARAM_STR|
PDO::PARAM_INPUT_OUTPUT,
4000);
echo “Got $valn”;
}

Multi-rowset queries
$stmt = $dbh->query(
“call sp_multi_results()”);
do {
while ($row = $stmt->fetch()) {
print_r($row);
}
} while ($stmt->nextRowset());

Binding columns
“SELECT extension, name from CREDITS”);
$stmt->bindColumn(‘extension’, $ext);
$stmt->bindColumn(‘name’, $name);
while ($stmt->fetch(PDO::FETCH_BOUND)) {
echo “Extension: $extn”;
echo “Author: $namen”;
}
}

Portability Aids
• PDO aims to make it easier to write db independent apps

• A number of hacks^Wtweaks for this purpose

Oracle style NULLs
• Oracle translates empty strings into NULLs

• $dbh->setAttribute(PDO::ATTR_ORACLE_NULLS, true)

• Translates empty strings into NULLs when fetching data

• But won’t change them on insert

Case folding
• The ANSI SQL standard says that column names are returned in upper
case

• High end databases (eg: Oracle and DB2) respect this

• Most others don’t

• $dbh->setAttribute(PDO::ATTR_CASE, PDO::CASE_UPPER);

LOBs

• Large objects are usually >4kb in size
• Nice to avoid fetching them until you need them
• Mature RDBMS offer LOB APIs for this
• PDO exposes LOBs as Streams

Fetching an image
“select contenttype, imagedata”
.“ from images where id=?”);
$stmt->execute(array($_GET[‘id’]));
$stmt->bindColumn(1, $type,
PDO::PARAM_STR, 256);
$stmt->bindColumn(2, $lob,
PDO::PARAM_LOB);
$stmt->fetch(PDO::FETCH_BOUND);
header(“Content-Type: $type”);
fpassthru($lob);

Uploading an image
$stmt = $db->prepare(“insert into images ”
. “(id, contenttype, imagedata)”
. “ values (?,?,?)”);
$id = get_new_id();
$fp = fopen($_FILES[‘file’][‘tmp_name’],‘rb’);
$stmt->bindParam(1, $id);
$stmt->bindParam(2, $_FILES[‘file’][‘type’]);
$stmt->bindParam(3, $fp, PDO::PARAM_LOB);
$stmt->execute();

Scrollable Cursors
• Allow random access to a rowset

• Higher resource usage than forward-only cursors

• Can be used for positioned updates (more useful for CLI/GUI apps)

Positioned updates
• An open (scrollable) cursor can be used to target a row for another
query

• Name your cursor by setting PDO::ATTR_CURSOR_NAME during
prepare()

• UPDATE foo set bar = ? WHERE CURRENT OF cursor_name

Questions?
• Find these slides on my blog and on slideshare.net

• My blog: http://netevil.org/

• Gold: http://troels.arvin.dk/db/rdbms/#select-limit-offset

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