Large Objects (LOBs)

At some point in your application, you might find that you need to store "large" data in your database. Large typically means "around 4kb or more", although some databases can happily handle up to 32kb before data becomes "large". Large objects can be either textual or binary in nature. PDO allows you to work with this large data type by using the PDO::PARAM_LOB type code in your PDOStatement::bindParam() or PDOStatement::bindColumn() calls. PDO::PARAM_LOB tells PDO to map the data as a stream, so that you can manipulate it using the PHP Streams API.

Пример #1 Displaying an image from a database

This example binds the LOB into the variable named $lob and then sends it to the browser using fpassthru(). Since the LOB is represented as a stream, functions such as fgets(), fread() and stream_get_contents() can be used on it.


<?php
$db = new PDO('odbc:SAMPLE', 'db2inst1', 'ibmdb2');
$stmt = $db->prepare("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);
?>

Пример #2 Inserting an image into a database

This example opens up a file and passes the file handle to PDO to insert it as a LOB. PDO will do its best to get the contents of the file up to the database in the most efficient manner possible.


<?php
$db = new PDO('odbc:SAMPLE', 'db2inst1', 'ibmdb2');
$stmt = $db->prepare("insert into images (id, contenttype, imagedata) values (?, ?, ?)");
$id = get_new_id(); // some function to allocate a new ID

// assume that we are running as part of a file upload form
// You can find more information in the PHP documentation

$fp = fopen($_FILES['file']['tmp_name'], 'rb');

$stmt->bindParam(1, $id);
$stmt->bindParam(2, $_FILES['file']['type']);
$stmt->bindParam(3, $fp, PDO::PARAM_LOB);

$db->beginTransaction();
$stmt->execute();
$db->commit();
?>

Пример #3 Inserting an image into a database: Oracle

Oracle requires a slightly different syntax for inserting a lob from a file. It's also essential that you perform the insert under a transaction, otherwise your newly inserted LOB will be committed with a zero-length as part of the implicit commit that happens when the query is executed:


<?php
$db = new PDO('oci:', 'scott', 'tiger');
$stmt = $db->prepare("insert into images (id, contenttype, imagedata) " .
"VALUES (?, ?, EMPTY_BLOB()) RETURNING imagedata INTO ?");
$id = get_new_id(); // some function to allocate a new ID

// assume that we are running as part of a file upload form
// You can find more information in the PHP documentation

$fp = fopen($_FILES['file']['tmp_name'], 'rb');

$stmt->bindParam(1, $id);
$stmt->bindParam(2, $_FILES['file']['type']);
$stmt->bindParam(3, $fp, PDO::PARAM_LOB);

$stmt->beginTransaction();
$stmt->execute();
$stmt->commit();
?>