PHP5中数据库抽象层: PDO

pdo是php5中新加入的数据库抽象层，为了解决访问不同数据库统一接口的问题。类似于PEAR::DB类和ADODB类的操作，不过它是直接封装再php扩展中，可以自由选择使用。

目前的php5.1beta中已经更好的加入了pdo的支持，我们下看具体帮助。

http://cn.php.net/pdo

为了描述清楚，我们把直接把帮助复制过来。

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PDO Functions

The PHP Data Objects (PDO) extension defines a lightweight, consistent interface for accessing databases in PHP. Each database driver that implements the PDO interface can expose database-specific features as regular extension functions. Note that you cannot perform any database functions using the PDO extension by itself; you must use a database-specific PDO driver to access a database server.

安装

Windows

Follow the same steps to install and enable the PDO drivers of your choice.

1. Windows users can download the extension DLL php_pdo.dll as part of the PECL collection binaries from /downloads.php or a more recent version from a PHP 5 PECL Snapshot.

2. To enable the PDO extension on Windows operating systems, you must add the following line to php.ini:

   extension=php_pdo.dll

3. Next, choose the other DB specific DLL files and either use dl() to load them at runtime, or enable them in php.ini below pdo_pdo.dll. For example:

   extension=php_pdo.dll
   extension=php_pdo_firebird.dll
   extension=php_pdo_mssql.dll
   extension=php_pdo_mysql.dll
   extension=php_pdo_oci.dll
   extension=php_pdo_oci8.dll
   extension=php_pdo_odbc.dll
   extension=php_pdo_pgsql.dll
   extension=php_pdo_sqlite.dll

   These DLL's should exist in the systems extension_dir.

Linux and UNIX

Due to a bug in the pear installer you should install the PDO package manually using the following steps:

Follow the same steps to install and enable the PDO drivers of your choice.

1. Download the PDO package to your local machine:

   bash$  wget http://pecl.php.net/get/PDO

2. Determine your PHP bin directory. If your PHP 5 CLI binary lives at /usr/local/php5/bin/php then the bin dir is /usr/local/php5/bin.

3. Set your path so that your PHP bin directory is at the front:

   export PATH="/usr/local/php5/bin:$PATH"

4. Manually build and install the PDO extension:

   bash$ tar xzf PDO-0.2.tgz
   bash$ cd PDO-0.2
   bash$ phpize
   bash$ ./configure
   bash$ make
   bash$ sudo -s
   bash# make install
   bash# echo extension=pdo.so >> /usr/local/php5/lib/php.ini

PDO Drivers

The following drivers currently implement the PDO interface:

Driver name Supported databases

PDO_DBLIB	FreeTDS / Microsoft SQL Server / Sybase
PDO_FIREBIRD	Firebird/Interbase 6
PDO_MYSQL	MySQL 3.x/4.0
PDO_OCI	Oracle Call Interface
PDO_ODBC	ODBC v3 (IBM DB2 and unixODBC)
PDO_PGSQL	PostgreSQL
PDO_SQLITE	SQLite 3.x

预定义类

PDO

Represents a connection between PHP and a database server.

构造函数

• PDO - constructs a new PDO object

方法

• beginTransaction - begins a transaction

• commit - commits a transaction

• exec - issues an SQL statement and returns the number of affected rows

• errorCode - retrieves an error code, if any, from the database

• errorInfo - retrieves an array of error information, if any, from the database

• getAttribute - retrieves a database connection attribute

• lastInsertId - retrieves the value of the last row that was inserted into a table

• prepare - prepares an SQL statement for execution

• query - issues an SQL statement and returns a result set

• quote - returns a quoted version of a string for use in SQL statements

• rollBack - roll back a transaction

• setAttribute - sets a database connection attribute

PDOStatement

Represents a prepared statement and, after the statement is executed, an associated result set.

方法

• bindColumn - binds a PHP variable to an output column in a result set

• bindParam - binds a PHP variable to a parameter in the prepared statement

• columnCount - returns the number of columns in the result set

• errorCode - retrieves an error code, if any, from the statement

• errorInfo - retrieves an array of error information, if any, from the statement

• execute - executes a prepared statement

• fetch - fetches a row from a result set

• fetchAll - fetches an array containing all of the rows from a result set

• fetchSingle - returns the data from the first column in a result set

• getAttribute - retrieves a PDOStatement attribute

• getColumnMeta - retrieves metadata for a column in the result set

• nextRowset - retrieves the next rowset (result set)

• rowCount - returns the number of rows that were affected by the execution of an SQL statement

• setAttribute - sets a PDOStatement attribute

• setFetchMode - sets the fetch mode for a PDOStatement

我们看第一组方法是查询的部分方法，第二组方法是获取数据集的方法。

我们看如何连接一个数据库。我们使用pdo的构造函数来连接数据库：

PDO::__construct

(no version information, might be only in CVS)

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

说明

PDO PDO::__construct ( string dsn [, string username [, string password [, array driver_options]]] )

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

参数

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. Examples of each driver are given below:

PDO_DBLIB

The DSN prefix is either sybase: or mssql: depending on which libraries it was linked against during compilation.

sybase:host=localhost; dbname=testdb

mssql:host=localhost; dbname=testdb

PDO_FIREBIRD

firebird:User=john;Password=mypass;Database=DATABASE.GDE;DataSource=localhost;Port=3050

PDO_MYSQL

mysql:host=localhost;dbname=testdb

PDO_OCI

To connect via tnsnames.ora, use:

oci:mydb

If using instantclient, use:

oci:dbname=//localhost:1521/testdb

PDO_ODBC

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

DSN=SAMPLE refers to the SAMPLE data source configured in the ODBC driver manager.

PDO_PGSQL

pgsql:host=localhost port=5432 dbname=testdb user=john password=mypass

Note, by passing user and password in the DSN, the username and password parameters become optional. If specified, they are glued to the end of the connection string.

PDO_SQLITE

sqlite:/path/to/database

To create a database in memory, use:

sqlite::memory:

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.

注: 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.

driver_options

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

返回值

Returns a PDO object on success.

异常

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

例

例子 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();
}

?>

例子 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();
}

?>

例子 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();
}

?>

其他的方法请参考手册：http://cn.php.net/pdo

说明：以上内容基本来源于手册，请自行参考手册获取更详细的内容。