PHP - Manual: PDO::__construct

2024-04-20

PDO::__construct

(PHP 5 >= 5.1.0, PHP 7, PHP 8, PECL pdo >= 0.1.0)

PDO::__construct — 创建一个表示数据库连接的 PDO 实例

说明

PDO::__construct(
    string $dsn,
    string $username = ?,
    string $password = ?,
    array $driver_options = ?
)

创建一个表示连接到请求数据库的数据库连接 PDO 实例。

参数

dsn

数据源名称或叫做 DSN，包含了请求连接到数据库的信息。

通常，一个 DSN 由 PDO 驱动名、紧随其后的冒号、以及具体 PDO 驱动的连接语法组成。更深入的信息能从 PDO 具体驱动文档找到。

The dsn 参数支持三种不同的方式创建一个数据库连接：

Driver invocation

dsn 包含完整的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.

注意:
别名必须得在 php.ini 中定义了，不能是在 .htaccess 或 httpd.conf 中。

username

DSN字符串中的用户名。对于某些PDO驱动，此参数为可选项。

password

DSN字符串中的密码。对于某些PDO驱动，此参数为可选项。

driver_options

一个具体驱动的连接选项的键=>值数组。

返回值

成功则返回一个PDO对象。

错误／异常

如果试图连接到请求的数据库失败，则PDO::__construct() 抛出一个 PDO异常（PDOException）。

范例

示例 #1 Create a PDO instance via driver invocation


<?php
/* Connect to an ODBC 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();
}

?>

示例 #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();
}

?>

示例 #3 使用别名创建一个PDO实例

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
/*  使用别名连接到一个ODBC数据库  */
$dsn = 'mydb';
$user = '';
$password = '';

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

?>

add a note

User Contributed Notes 13 notes

down

123

Kiipa at live dot com ¶

8 years ago


To get UTF-8 charset you can specify that in the DSN.

$link = new PDO("mysql:host=localhost;dbname=DB;charset=UTF8");

down

piotrekkr at o2 dot pl ¶

11 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.

down

subme at interia dot pl ¶

13 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';
?>

down

daviddlavier at gmail dot com ¶

6 years 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.

down

Aymeric S ¶

1 year ago


When trying to connect to a local database, it seems "uri:file:///" is no longer needed. Just write the PDO pilot name followed by the absolute path of the file.
Example : sqlite:C:\VirtualHosts\phpliteadmin\dbs\surveillance_logeas.s3DB

down

Francesco Montanari ¶

2 years ago


Most of the information in the comment here is outdated or wrong.

You do can use host=localhost to connect via socket, which is faster than TCP, so setting 127.0.0.1 is a performance loss.

To use proper utf you should use utf8mb4, for example:

$db = new PDO('mysql:host=' . DATABASE_HOST . ';dbname='. DATABASE_NAME .';charset=utf8mb4', DATABASE_USER, DATABASE_PASSWORD);

down

Victor T. ¶

12 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\''));

?>

down

Anonymous ¶

9 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.

down

ohcc at 163 dot com ¶

6 years 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();
    }    
?>

down

453034559 at qq dot com ¶

4 months ago


// set DEFAULT_FETCH_MODE
<?php
    try {
        $p = new PDO("mysql:host=$db_host;port=$db_port;dbname=$db_dbname", $db_user, $db_pass,array(
            PDO::ATTR_DEFAULT_FETCH_MODE =>PDO::FETCH_ASSOC,
            PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8', //after php5.3.6
        ));
        //$p->exec('SET NAMES utf8');
    } catch (PDOException $e) {
        print "Error!: " . $e->getMessage() . "<br/>";
        die();
    }
?>

down

-2

berk0081 at umn dot edu ¶

7 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");

?>

down

-11

srycroft at excelsystems dot com ¶

5 years 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

down

-21

olivernybroe at gmail dot com ¶

6 years 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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官方地址：https://www.php.net/manual/en/pdo.construct.php

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PHP官方手册 - 互联网笔记

PDO::__construct

说明

参数

返回值

错误／异常

范例

User Contributed Notes 13 notes