Drupal编程指南：原理、实践与陷阱（第2版）

Drupal

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CHAPTER 1

Overview of Drupal

This chapter contains overviews of the Drupal software and open-source project, how

Drupal has evolved from its beginnings through the latest version (Drupal 8), how

Drupal performs its core function (handling HTTP requests), the Drupal cache system,

and Drupal’s automatic class loading system. You will need to be familiar with this

information in order to understand and use the rest of the book, so you’ll probably want

to at least skim through it, if not read it in depth.

What Is Drupal?

Depending on who you talk to, you’ll hear Drupal called a Content Management Sys‐

tem (CMS) or a Content Management Framework (CMF, a platform that you can use to

build a custom CMS)--and both are accurate. It can be called a CMS because after

installing only the base Drupal software, you can create a basic website and manage the

content online. On the other hand, it can be called a flexible CMF because most people

choose to add additional modules to Drupal in order to build more complicated websites

with more features, and Drupal also allows you to create fully custom modules.

Drupal is free and open-source software (FOSS), governed by the GNU General Public

License (GPL) version 2 (or, at your option, any later version). The licensing means that

Drupal is free for you, or anyone else in the world, to download, use, and modify, as

long as you comply with the license terms.

If you have never read the GPL and plan to use Drupal, you would

be well advised to do so (even more so if you plan to do any Drupal

programming, for yourself or others). The GPL governs not only what

you can do with Drupal software itself, but also what you can do with

any add-ons you download from drupal.org, code you find on dru‐

pal.org documentation pages, and any derivative work (work that

contains GPL-licensed work, verbatim or with modifications) that

you or others create. It’s also written in plain English and is quite a

good read (for programmer-types anyway); you can find it in the

LICENSE.txt file distributed with Drupal core, or at http://gnu.org.

And finally, Drupal is also a project and a community. Unlike some FOSS software that

is developed primarily by one company that later releases the source code to the public,

Drupal is continually evolving due to the efforts of a world wide community of indi‐

viduals and companies who donate their time and money to create and test Drupal

software, write the documentation, translate it into other languages, answer support

questions, keep the drupal.org web servers running, and organize get-togethers on a

local and world wide scale.

Drupal Core

Drupal core is the name of the package you can download from https://drupal.org/

project/drupal, consisting of a set of PHP scripts (some with embedded HTML mark-

up), JavaScript, CSS, and other files. This software interacts with a web server (typically,

Apache), a database (MySQL, PostgreSQL, and SQLite are supported by Drupal core

versions 7 and 8, and others are supported by add-on modules), and a web browser to

provide the basics of a CMS:

• A URL request dispatch system

•

A user account management system with flexible permissions and roles

• Online content editing

• An API for Drupal programmers

• A module system, which lets you enable and disable functionality in a modular way,

and download additional code to expand functionality

•

A theme (template) system, which lets you override how everything from a button

to an entire page is displayed

• An installation profile system, which governs what modules and themes are in‐

stalled when you first install Drupal, and allows downloading of complete Drupal

distributions for special-purpose sites

•

An internationalization system, which allows you to translate your site into other

languages

2 | Chapter 1: Overview of Drupal

• A block system that allows you to place chunks of content in various regions of a

site’s pages.

• A navigation menu builder

• A flexible taxonomy system that supports categories, tags, and user-defined

taxonomy vocabularies

• Optional modules supporting commenting, content fields, RSS aggregation, search,

lists of content and other site components, and site features such as forums and

polls (depending on the Drupal version, some of these may require downloading

add-on modules instead of being part of Drupal core)

•

The ability to set up a site in different languages and translate content (depending

on the Drupal version, some add-on modules may be required to make a multi-

lingual or non-English site)

•

Logging of system events and errors

• An automatic class-loading system

• In Drupal 8, a file-based configuration management system

•

In Drupal 8, a plugin API, which is used in many Drupal systems

• In Drupal 8, the services concept and the dependency injection container, which

allow overrides of basic Drupal functionality.

Drupal Add-Ons: Modules, Themes, Distributions, and Translations

Drupal is modular software, meaning that you can turn site features and functionality

on and off by enabling and disabling modules. In Drupal 7 and earlier versions, you can

disable a module to turn off its functionality while retaining its data so it can be enabled

again. However, in Drupal 8 this is not allowed: to turn off a module you have to uninstall

it completely, losing its data. Drupal core comes with a few required modules and several

optional modules; you can download thousands of additional contributed modules from

https://drupal.org/project/modules. Most modules have configuration options that you

can modify from the Drupal administration interface, by logging in to the Drupal-based

site using an account that has been given appropriate permissions. The permission

system is flexible: you can define named roles, which are granted specific permissions

(the permissions are defined by modules), and you can assign one or more roles to each

user account.

Drupal’s theme system separates the content from the specific HTML markup and styl‐

ing. This means that if you want to redesign the site’s layout or styling, you can do so

by downloading a new theme from https://drupal.org/project/themes, purchasing a

commercially available theme, or creating one yourself—once installed and enabled, it

takes effect immediately to change the look of your site without the necessity of editing

What Is Drupal? | 3

your content pages. The theme system has a cascading system of inheritance and over‐

rides, including the ability to define_sub-themes_, which allows you to use the default

display or the display from a theme you have downloaded for some aspects of the output,

and override the parts you want to change; the overrides can be at anything from the

lowest level (for example, the presentation of buttons) to the full page.

You can also download Drupal in a distribution, which consists of Drupal core, an

installation profile, and a collection of contributed modules and themes that work to‐

gether to provide a more functional site for a specific purpose. Distributions are available

at https://drupal.org/project/distributions for e-commerce, government, non-profits,

and many other purposes.

And finally, you can download translations for Drupal and its contributed modules,

themes, and distributions from https://localize.drupal.org. This allows you to build a

non-English language site fairly easily with both Drupal 7 and Drupal 8. Multilingual

sites can also be built using Drupal; in Drupal 7, this requires downloading several

contributed modules and is fairly complex, but Drupal 8 core has much more multi‐

lingual functionality built in, so the situation should be much improved. See https://

www.drupal.org/documentation/multilingual for more on building multilingual sites.

Finding Drupal add-ons

Here are the main ways to find Drupal add-ons (modules, themes, or distributions):

• To find a specific add-on that you know the name of, visit https://drupal.org and

type the name into the search box.

• If it’s not in the first few results, try restricting the search to modules or themes,

using the filters in the right sidebar (there is no way to restrict to distributions from

a drupal.org search, as of fall 2014).

• Alternatively, start by navigating to https://drupal.org/project/modules, https://

drupal.org/project/themes, or https://drupal.org/project/distributions, and search‐

ing from there. You can also search from these pages by keyword, Drupal version

compatibility, or category (for modules only).

• You can try guessing the URL, which is always drupal.org/project/, followed by the

machine name of the project. The machine name is composed of lowercase letters,

numbers, and underscores, but since the machine names are chosen by developers,

some are hard to guess and they may take a couple of tries. For example, the Panels

module is at https://drupal.org/project/panels; the Omega theme is at https://

drupal.org/project/omega; the XML Sitemap module is at https://drupal.org/project/

xmlsitemap.

•

And of course, you can always try your favorite web search engine, with keywords

“Drupal module” and the name of the module.

4 | Chapter 1: Overview of Drupal

The Evolution of Drupal

Drupal started out as a message board, created by founder Dries Buytaert at the Uni‐

versity of Antwerp, in 1999. Once this message board was established, its members

started exploring ideas for its improvement, and these were added to the software.

Eventually, Dries named the software Drupal, and released it as an open-source project

so others could work on it, on January 15, 2001. By June 2002, when version 4.0.0 was

released, Drupal had expanded to a more flexible CMS, with modules handling blogs,

polls, taxonomy, and generic content, as well as the forums that it started with, and a

system for add-on modules and themes. The 4.x.y, 5.x, and 6.x versions continued the

process of adding new CMS functionality and refining the API.

Don’t worry if you don’t know what all of the terminology in this

section means yet! It will be explained later in the book, where pro‐

gramming with each of the related sub-systems of Drupal is explored.

January 2011 saw the first full release of Drupal version 7, which brought several major

changes to the Drupal software and its API:

• There was a major usability push. A group formed to do usability testing, and many

of its findings resulted in the redesign of administrative pages.

• The accessibility of the administrative interface was also vastly improved, due to

the efforts of a dedicated group of people interested in accessibility, and the recog‐

nition in the Drupal community as a whole of its importance.

• A completely new database API, based on PHP’s PDO library, was added. This took

Drupal 6’s concept of database portability, which was accomplished through a set

of wrapper functions, and made it object-oriented, more robust, more secure, and

more industry-standard.

• A class auto-loader was created and added to Drupal core.

• The concept of entities was introduced, encompassing content items from the Node

module, user accounts, taxonomy terms, and comments. The system also allowed

add-on modules to define their own entity types.

•

In conjunction with entities, a system for fields on entities was added to Drupal

core (previously, this had been in the CCK contributed module, and it only worked

on Node content items). Many field modules were also added to Drupal core, in‐

cluding modules to handle file and image uploads, and output images in different

sizes. Since nearly every Drupal site needs this functionality, getting it into Drupal

core was a key Drupal 7 milestone.

The Evolution of Drupal | 5

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Drupal编程指南：原理、实践与陷阱（第2版）

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