PHP 7.1.0 Released

PDO::__construct

(PHP 5 >= 5.1.0, PHP 7, PECL pdo >= 0.1.0)

PDO::__construct Creates a PDO instance representing a connection to a database

Descrierea

public PDO::__construct ( string $dsn [, string $username [, string $password [, array $options ]]] )

Creates a PDO instance to represent a connection to the requested database.

Parametri

dsn

The Data Source Name, or DSN, contains the information required to connect to the database.

In general, a DSN consists of the PDO driver name, followed by a colon, followed by the PDO driver-specific connection syntax. Further information is available from the PDO driver-specific documentation.

The dsn parameter supports three different methods of specifying the arguments required to create a database connection:

Driver invocation

dsn contains the full DSN.

URI invocation

dsn consists of uri: followed by a URI that defines the location of a file containing the DSN string. The URI can specify a local file or a remote URL.

uri:file:///path/to/dsnfile

Aliasing

dsn consists of a name name that maps to pdo.dsn.name in php.ini defining the DSN string.

Notă:

The alias must be defined in php.ini, and not .htaccess or httpd.conf

username

The user name for the DSN string. This parameter is optional for some PDO drivers.

password

The password for the DSN string. This parameter is optional for some PDO drivers.

options

A key=>value array of driver-specific connection options.

Valorile întoarse

Returns a PDO object on success.

Erori/Excepții

PDO::__construct() throws a PDOException if the attempt to connect to the requested database fails.

Exemple

Example #1 Create a PDO instance via driver invocation

<?php
/* Connect to a MySQL database using driver invocation */
$dsn 'mysql:dbname=testdb;host=127.0.0.1';
$user 'dbuser';
$password 'dbpass';

try {
    
$dbh = new PDO($dsn$user$password);
} catch (
PDOException $e) {
    echo 
'Connection failed: ' $e->getMessage();
}

?>

Example #2 Create a PDO instance via URI invocation

The following example assumes that the file /usr/local/dbconnect exists with file permissions that enable PHP to read the file. The file contains the PDO DSN to connect to a DB2 database through the PDO_ODBC driver:

odbc:DSN=SAMPLE;UID=john;PWD=mypass

The PHP script can then create a database connection by simply passing the uri: parameter and pointing to the file URI:

<?php
/* Connect to an ODBC database using driver invocation */
$dsn 'uri:file:///usr/local/dbconnect';
$user '';
$password '';

try {
    
$dbh = new PDO($dsn$user$password);
} catch (
PDOException $e) {
    echo 
'Connection failed: ' $e->getMessage();
}

?>

Example #3 Create a PDO instance using an alias

The following example assumes that php.ini contains the following entry to enable a connection to a MySQL database using only the alias mydb:

[PDO]
pdo.dsn.mydb="mysql:dbname=testdb;host=localhost"
<?php
/* Connect to an ODBC database using an alias */
$dsn 'mydb';
$user '';
$password '';

try {
    
$dbh = new PDO($dsn$user$password);
} catch (
PDOException $e) {
    echo 
'Connection failed: ' $e->getMessage();
}

?>

Notă:

Before PHP5.3, a class which extends PDO and implements __call magic will always receive lower case $method.

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User Contributed Notes 13 notes

up
89
Kiipa at live dot com
3 years ago
To get UTF-8 charset you can specify that in the DSN.

$link = new PDO("mysql:host=localhost;dbname=DB;charset=UTF8");
up
26
piotrekkr at o2 dot pl
6 years ago
To connect throught unix socket you need to use
<?php
$dsn
= 'mysql:dbname=testdb;unix_socket=/path/to/socket';
?>

You musn't specify host when using socket.
up
24
Victor T.
6 years ago
If you use the UTF-8 encoding, you have to use the fourth parameter :

<?php
$db
= new PDO('mysql:host=myhost;dbname=mydb', 'login', 'password', array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES \'UTF8\''));
?>
up
19
subme at interia dot pl
8 years ago
To specify a database connection port use the following DSN string

<?php
$dsn
= 'mysql:dbname=testdb;host=127.0.0.1;port=3333';
?>
up
9
daviddlavier at gmail dot com
1 year ago
I'd like to point out that in PHP 7.0 in the dsn parameter you can't use 'host=localhost' to solve this you can use 'host=127.0.0.1' instead.
up
9
Anonymous
2 years ago
To connect to the database via a function use this and call the getConnection function in the class constructor.

<?php
class Connection{

    protected
$db;

    public function
Connection(){

   
$conn = NULL;

        try{
           
$conn = new PDO("mysql:host=localhost;dbname=dbname", "dbuser", "dbpass");
           
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            } catch(
PDOException $e){
                echo
'ERROR: ' . $e->getMessage();
                }   
           
$this->db = $conn;
    }
   
    public function
getConnection(){
        return
$this->db;
    }
}

?>
up
6
Anonymous
3 years ago
Sqlite:

<?php
try{    
   
$pdo = new PDO('sqlite:example.db');
}catch (
PDOException $e){
     die (
'DB Error');
}
?>

If 'example.db' does not exist, no exception is thrown but the file 'example.db' is created.
up
3
berk0081 at umn dot edu
2 years ago
Although not explicitly stated, parameters in the PDO $dsn string may be case-sensitive on some platforms or drivers.

<?php
// The dbname will not be parsed with incorrect casing:
$pdo = new PDO("mysql:host=hostname;DBName=database", "user", "password");

// The correct dbname is lowercase, as displayed in the manual:
$pdo = new PDO("mysql:host=hostname;dbname=database", "user", "password");
?>
up
1
ohcc at 163 dot com
1 year ago
You will get a fatal error if you don't catch the exception threw by PDO when it fails to connect to the database server like this.

Fatal error: in xxx.php on line xx

This error neither can be handled by error handlers nor can it be erased by the @ sign, which can make your script uncontrollable.

<?php
    $db
= new pdo('mysql:host=127.0.0.1;port=3306;dbname=mysql;charset=utf8','user','password',array(
       
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
    ));
?>

You should always try ... catch ...

<?php
   
try{
   
$db = new pdo('mysql:host=127.0.0.1;port=3306;dbname=mysql;charset=utf8','user','password',array(
       
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
    ));
    }catch(
PDOException $pe){
        echo
$pe->getMessage();
    }   
?>
up
-5
ohcc at 163 dot com
1 year ago
<?php
   
// PDO::__construct can end up with a fatal error rather than throw an exception even if you try ... catch ... .
   
try{
       
$db = new PDO(
           
// a database to which connection may fail
           
'mysql:host=www.wuxiancheng.cn; dbname=php; port=3306; charset=utf8',
           
'root',
           
'rx00t',
            array(
               
PDO::ATTR_ERRMODE=>PDO::ERRMODE_EXCEPTION,
               
PDO::ATTR_TIMEOUT=>1,
            )
        );
    }catch(
PDOException $pe){
       
       
// test the following lines of code respectively, and you will find the first line and the second line will end up with a fatal error.
       
       
throw $pe; // Fatal error: in path\file.php on line n, script ends, no exception thrown       

       
throw new PDOException($pe->getMessage()); //Fatal error: in path\file.php on line n, script ends, no exception thrown       
       
       
throw new PDOException ('cannot connect to the database'); // an exception is thrown as expected
       
       
throw new PDOException('error: '.$pe->getMessage()); //Fatal error: in path\file.php on line n, script ends, no exception thrown       

       
throw new PDOException($pe->getLine()); // an exception is thrown as expected

       
throw new PDOException($pe->getFile()); // an exception is thrown as expected

       
throw new PDOException($pe->getCode()); // an exception is thrown as expected

       
throw new PDOException($pe->getTraceAsString()); // an exception is thrown as expected
   
}
?>
up
-6
info at salientdigital dot com
1 year ago
If you happen to create a dsn like this...

<?php
   
//wrong dsn
   
$db = new PDO('mysql:database=yourdb;host=127.0.0.1', 'user', 'password');
   
$stmt = $db->prepare('SELECT * FROM tbl WHERE id = :id');
   
$stmt->bindParam(':id', $user_id, PDO::PARAM_INT);
   
$result = $stmt->execute();
?>

... your result will be bool(false) and your $db->errorInfo() will be "0000" which isn't very helpful.

You have to look to the $stmt->errorInfo() to see "No database selected" which is even more confusing until you realize that it's not 'database' but 'dbname' in your DSN! You would think the error about a bad DSN would be in the $db errorInfo but it is not, it's not until you try the $stmt that the error is generated.

<?php
   
//correct dsn
   
$db = new PDO('mysql:dbname=yourdb;host=127.0.0.1', 'user', 'password');
?>

I wasted a half hour on that one.
up
-1
srycroft at excelsystems dot com
4 months ago
For IBM i / iSeries / AS400 DB2 connections, you can specify system naming and library lists for php_pdo modules > 1.3.3-sg2

<?php
   $pdo
= new PDO(
    
'ibm:' . $host,
    
$user,
    
$password,
     array(
      
PDO::I5_ATTR_DBC_SYS_NAMING => true,
      
PDO::I5_ATTR_DBC_LIBL => "QGPL QSYS"
    
)
   );
?>

See http://yips.idevcloud.com/wiki/index.php/XMLSERVICE/PHPPDOChangeLog
up
-3
olivernybroe at gmail dot com
7 months ago
The PDO connection is case-sensitive, this means that you cannot write
`$PDO = new PDO("MySQL:DBName=dbname;host=localhost");`
You would have to write it
`$PDO = new PDO("mysql:dbname=dbname;host=localhost");`

The difference here is that `mysql` and `dbname` is with all lower-case.

Some IDE's like PHPStorm will show a `TYPO ERROR`, at `dbname` if it's written with lower-case only, this is just to be ignored and have been reported to PHPStorm for them to fix. (Currrent version 10.0.2)
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