PHP数据对象入门指南：5版数据库连接抽象

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《Learning PHP Data Objects》是一本面向初学者的PHP数据对象指南，它着重于PHP 5中的数据库连接抽象库。作者是Dennis Popel，该书由Packt Publishing出版，版权日期为2007年9月。本书旨在帮助读者深入了解如何在PHP开发中有效地管理和操作数据库，通过提供实践性的教程和深入讲解，使读者掌握数据对象模型，理解如何设计和实现数据访问层，以及如何利用抽象化的数据库连接技术。在本书中，读者可以期待学习以下核心知识点： 1. **PHP基础知识**：首先，读者将回顾PHP语言的基础概念，包括变量、数据类型、控制结构和函数，以便为后续的数据对象处理打下坚实基础。 2. **数据库连接**：章节将详细讲解如何使用PHP与各种类型的数据库（如MySQL、Oracle、PostgreSQL等）进行安全和高效地连接。这包括连接参数的设置，错误处理和最佳实践。 3. **数据库抽象层**：作者会介绍PHP Data Objects (PDO) 和 MySQLi等PHP内置的数据库抽象层，讨论它们的优点，如统一接口、异常处理和事务支持，以及如何选择适合项目需求的抽象方式。 4. **对象关系映射（ORM）**：书中可能会涵盖ORM的概念，解释如何通过ORM工具如Doctrine或Propel来简化数据访问，减少SQL编写工作，提高开发效率。 5. **数据查询与操作**：学习如何执行CRUD（创建、读取、更新、删除）操作，包括预编译语句、参数化查询以防止SQL注入，以及如何处理结果集。 6. **性能优化**：对于数据库性能的考虑，读者将了解如何设计高效的查询、索引和缓存策略，以确保应用程序在高并发环境下的稳定运行。 7. **最佳实践和安全建议**：书中会强调开发过程中的一些最佳实践，如代码重构、异常处理、安全措施（如使用预处理语句）以及遵循PHP安全编码规范。 8. **示例和项目实战**：为了增强理解和记忆，本书会包含大量的代码示例和小型项目，让读者有机会将所学知识应用到实际环境中。 9. **版本更新与兼容性**：由于PHP和数据库技术的不断进步，读者还会了解到新版本PHP和数据库API的更新，以及如何确保项目与最新技术的兼容性。《Learning PHP Data Objects》是一本实用的教程，适合希望提升PHP数据库开发技能的开发者，无论是初级开发者还是希望扩展知识库的专业人士。通过阅读这本书，读者将能够构建更健壮、可维护且安全的PHP应用程序。

Introduction

PHP Data Objects, (PDO) is a PHP5 extension that denes a lightweight DBMS

connection abstraction library (sometimes called data access abstraction library).

The need for a tool like PDO was dictated by the great number of database systems

supported by PHP. Each of these database systems required a separate extension

that dened its own API for performing the same tasks, starting from establishing a

connection to advanced features such as preparing statements and error handling.

The fact that these APIs were not unied made transition between underlying

databases painful, often resulting in the rewriting of many lines of code, which in

turn, led to new programming errors that required time to track, debug and correct.

On the other hand, the absence of a unied library, like JDBC for Java, was putting

PHP behind the big players in the programming languages world. Now that such

library exists, PHP is regaining its position and is a platform of choice for millions

of programmers.

It should be noted, however, that there exist several libraries written in PHP, that

serve the same purpose as PDO. The most popular are the ADOdb library and the

PEAR DB package. The key difference between them and PDO is speed. PDO is a

PHP extension written in a compiled language (C/C++), while the PHP libraries

are written in an interpreted language. Also, once PDO is enabled, it does not

require you to include source les in your scripts and redistribute them with your

application. This makes installing your applications easier, as the end user does not

need to take care of third-party software.

Here, we are neither comparing these libraries with PDO nor advocating

the use of PDO over such libraries. We are just showing the advantages

and disadvantages of this extension. For example, the PEAR package,

MDB2, has richer functionality of an advanced database abstraction

library, which PDO does not.

Chapter 1

[ 7 ]

As you can see, all three databases require quite different ways of opening a

connection. While this is not a problem now, but if you always use the same database

management system in case you need to migrate, you will have to rewrite

your scripts.

Now, let's see what PDO has to offer. As PDO is fully object-oriented, we will be

dealing with connection objects, and further interaction with the database will

involve calling various methods of these objects. The examples above implied the

need for something analogous to these connection objects—calls to mysql_connect

or pg_connect return link identiers and PHP variables of a special type: resource.

However, we didn't use connection objects then since these two database APIs

don't require us to explicitly use them if we only have one connection in our scripts.

However, SQLite always requires a link identier.

With PDO, we will always have to explicitly use the connection object, since there

is no other way of calling its methods. (Those unfamiliar with object-oriented

programming should refer to Appendix A).

Each of the three above connections could be established in the following manner:

// For MySQL:

$conn = new PDO("mysql:host=$host;dbname=$db", $user, $pass);

// For SQLite:

$conn = new PDO("sqlite:$db");

// And for PostgreSQL:

$conn = new PDO("pgsql:host=$host dbname=$db", $user, $pass);

As you can see, the only part that is changing here is the rst argument passed to the

PDO constructor. For SQLite, which does not utilize username and password, the

second and third arguments can be skipped.

SQLite is not a database server, but it is an embedded SQL database

library that operates on local les. More information about SQLite can be

found at www.sqlite.org and more information about using SQLite

with PHP can be found at www.php.net/sqlite. Information about

using SQLite with PDO can be obtained from www.php.net/manual/

en/ref.pdo-sqlite.php

Connection Strings

As you have seen in previous example, PDO uses the so-called connection strings

(or Data Source Names, abbreviated to DSN) that allow the PDO constructor to select

proper driver and pass subsequent method calls to it. These connection strings or

DSNs are different for every database management system and are the only things

that you will have to change.

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