PDO::__construct
Creates a PDO instance representing a connection to a database
Description
public PDO::__construct(
string $dsn,
stringnull $username = null,
#[\SensitiveParameter]stringnull $password = null,
arraynull $options = null
)
Parameters
-
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.
Note:
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.
Errors/Exceptions
PDO::__construct throws a PDOException if the attempt
to connect to the requested database fails, regardless of which PDO::ATTR_ERRMODE is currently set.
Examples
Example #1 Create a PDO instance via driver invocation
<?php
$dsn = 'mysql:dbname=testdb;host=127.0.0.1';
$user = 'dbuser';
$password = 'dbpass';
$dbh = new PDO($dsn, $user, $password);
?>
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
$dsn = 'uri:file:///usr/local/dbconnect';
$user = '';
$password = '';
$dbh = new PDO($dsn, $user, $password);
?>
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
$dsn = 'mydb';
$user = '';
$password = '';
$dbh = new PDO($dsn, $user, $password);
?>