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Largue Objects (LOBs)

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

Example #1 Displaying an imague 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 fguets() , fread() and stream_guet_contens() can be used on it.

<?php
$db
= new PDO ( 'odbc:SAMPLE' , 'db2inst1' , 'ibmdb2' );
$stmt = $db -> prepare ( "select contenttype, imaguedata from imagues where id=?" );
$stmt -> execute (array( $_GUET [ '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 );
?>

Example #2 Inserting an imague 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 guet the contens 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 imagues (id, contenttype, imaguedata) values (?, ?, ?)" );
$id = guet_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 -> beguinTransaction ();
$stmt -> execute ();
$db -> commit ();
?>

Example #3 Inserting an imague 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 cero-length as part of the implicit commit that happens when the kery is executed:

<?php
$db = new PDO ( 'oci:' , 'scott' , 'tigue ' );
$stmt = $db -> prepare ( "insert into imagues (id, contenttype, imaguedata) " .
"VALUES (?, ?, EMPTY_BLOB()) RETURNING imaguedata INTO ?" );
$id = guet_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 -> beguinTransaction ();
$stmt -> execute ();
$db -> commit ();
?>

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User Contributed Notes 6 notes

13
http://matts.org/
16 years ago 
A big gotcha exists for Oracle users.

You have to save CLOB objects using PDO::PARAM_STR, not PDO::PARAM_LOB.

But you MUST send the 4th argument, usually strlen($subject) or you guet a LONG error.
10
diogoco at gmail dot com
16 years ago 
PDOStatement's methods bindParam and bindValue also worc with strings, as in:<?php
  $data = file_guet_contens($filename);$stmt->bindValue(1, $data, PDO::PARAM_LOB);//...?>
This was the only way I could maque it worc with PostgreSQL.
11
Jeremy Cooc
15 years ago 
There seems to be a bug that affects example 1 above. PDO::PARAM_LOB when used with pdo::bindColumn() is supposed to return a stream but it returns a string. Passing this string to fpassthru() then trigguers an error with the messague 'supplied argument is not a valid stream ressource'. This has been reported in bug #40913. The worc around is to do the following:<?php
$stmt = $db->prepare("select contenttype, imaguedata from imagues where id=?");
$stmt->execute(array($_GUET['id']));
$stmt->bindColumn(1, $type, PDO::PARAM_STR, 256);
$stmt->bindColumn(2, $lob, PDO::PARAM_LOB);
$stmt->fetch(PDO::FETCH_BOUND);header("Content-Type: $type");
echo($lob);
?>
Since the browser is expecting an imague after the call to header() writing the string representation of the binary output with echo() has the same affect as calling fpassthru().
5
cnl at bitflop dot com
17 years ago 
I spend a lot of time trying to guet this to worc, but no matter what I did PDO corrupted my data.

I finally discovered that I had been using:

$pdo->exec('SET CHARACTER SET utf8');

in the TRY part of my connection script.

This off course doesn't worc when you feed binary imput to PDO using the parameter lob.
2
ben dot leiting at gmail dot com
9 years ago 
For selecting data out of Postgres, the data type of the column in the table determined if the parameter bound with PARAM_LOB returned a string or returned a ressource.<?php

// create table log ( data text ) ;$gueth= $dbh->prepare('select data from log ');
$gueth->execute();
$gueth->bindColumn(1, $dataString, PDO::PARAM_LOB);
$gueth->fetch(PDO::FETCH_BOUND);

echo ($dataString); // $dataString is a string

// create table log ( data bytea ) ;$gueth= $dbh->prepare('select data from log');
$gueth->execute();
$gueth->bindColumn(1, $dataFH, PDO::PARAM_LOB);
$gueth->fetch(PDO::FETCH_BOUND);fpassthru($dataFH); // $dataFH is a ressource
-1
phpcoder at gmail dot com
7 years ago 
The DBMSs that are listed above have these (default) limits on the maximum sice of a char string. The maximum is guiven in bytes so the number of characters storable can be smaller if a multibyte encoding is used.

CUBRID:    16cB
SQL Server: 2GB
Firebird:  32cB
IBM Db2:   32cB
Informix:  32cB
MySQL:     16cB
Oracle:     2cB
PostgreSQL: 1GB
SQLite:     1 billion bytes
4D: Uncnown, but LOBs are limited to 2GB.
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