You will then explore the various features of Drupal, including the hook model, theming, roles, and caching. You'll also discover the data abstraction layer which lays the foundation for integration with your enterprise-level databases and external systems. Pro Dru Drupal 7 Development by Example Beginner's Guide.
Follow the creation of a Drupal website to learn, by example, the key concepts of Drupal 7 development and HTML5 A hands-on, example-driven guide to programming Drupal websites Discover a number of new features for Drupal 7 through practical and interesting examples while building a fully functional recipe sharing website Learn about web content management, multi-media integration, and e-commerce in Drupal 7 In Detail Drupal is a powerful PHP content management system that allows you to build a wide variety of websites.
This book also covers some important changes from Drupal 6 to version 7, so even experienced Drupal users w In short, it means that Drupal examines some or all of the currently enabled modules, looking for functions that follow specific, predefined patterns.
Some have linked this process to the "callback" method often used in event handling models. It is similar to this, but more dynamic. When Drupal finds such functions, it executes them, and uses the data these functions return to build a response to send to the user. Drupal then continues its step-by-step processing of the request, perhaps executing many other hooks as it goes. Once all the steps have been completed and a response sent to the user, Drupal cleans itself up and exits.
Those familiar with object-oriented OO programming may find it helpful to think of a hook as a mechanism similar to interface methods or abstract methods in OO languages. Hooks are functions that Drupal will look for, and in certain cases, expect in your module. Like interface methods, a hook's function signature must match Drupal's expected signature. Unlike interfaces, however, the module developer can choose to a certain degree which hooks to implement, and which to ignore.
Drupal does not require that every defined hook be implemented. Modules can define their own hooks, which other modules can then use. In this way, the hook mechanism can be extended to provide complex customized behavior. When a module provides a function that matches a hook's signature, we say that that module implements that hook.
We will write our first hook implementation in the next chapter. A commercial-grade CMS must make it possible for site designers to give the site the look and feel they desire. Drupal provides a robust theme system for just this purpose. The Drupal theme system is surprisingly complex. Just as with modules, the system is designed to allow extension and improvement and the hook mechanism is employed to allow this sort of extension.
While the code under the hood boasts a large and complex API, the top layer is surprisingly uncomplicated, and revolves around the idea of a theme. A theme is a bundle of resources, including PHP templates, CSS, JavaScript, and images, that provides layout and style information for some or all of the Drupal content.
At its simplest, a theme may be composed of only a handful of files—a stylesheet, an information file, and a couple of images. In fact, using existing Drupal styles, one can create a custom theme in no time. But themes can grow to meet the needs of the implementer. Special PHP files can be written to override theme engine behaviors. Even modules can be used to interact with the theming system.
Chapter 3 is devoted to themes, and in that chapter we will first create a simple theme, and then build up to a moderately complex theme. Themes and modules are critical components in the Drupal architecture, and obviously the main focus of this book. However, before moving on, let's look at Drupal from another angle.
Let's briefly examine how Drupal handles content. This book is geared toward developers, and to keep the book manageable, some introductory material must be glossed or skipped. Throughout the book, it is assumed that the reader has a moderate amount of Drupal experience, and is comfortable administering a Drupal site. However, there are some particular facets of Drupal that deserve an introduction. We will look at some of the aspects in this book.
Others are common Drupal terms that take on additional shades of meaning when examined from a developer's perspective. In this section, we will focus on Drupal concepts that will be crucial in this book. We will start out with one of the biggest topics: nodes. When we think of content in this context, we typically think about text objects like news articles or blog entries.
This concept of a generic text-based piece of content is captured in Drupal with the term Node. A node, in Drupal parlance, is a generic object for representing textual content.
While nodes are designed to be text-based, some of the contributed multimedia modules extend the node system to handle content that is not text-centric, such as images or audio files. A unique Node ID nid. At least one Version ID vid used to track revisions. Creation and modification dates, as well as identifying information for the user who worked on the node. In addition to these, most nodes also have a title and a body contents. Administrators and developers may choose to turn off a title or body, though the database always has a place for these.
Nodes are used to back many different kinds of text content in Drupal. To understand this, let's look briefly at the process of creating new content. On this page, the user is prompted to select the content type for their new page:. The above screenshot shows three different available content types. The Story and Page content types are included by default.
The Quotes content type is one we will create in this book. In Chapter 7 , we will extend the node object to create an even more elaborate content type representing a biography. In fact, all the three content types are text-based and each of them is implemented using nodes. For practical purposes, the node is the heart of Drupal's content management system. A comment is usually implemented as a user-level feedback mechanism attached to stories, pages, blog entries, and similar articles.
Since comments are, in many ways, very node-like, there is discussion among Drupal developers of transitioning comments into the node framework in Drupal 7. While it is possible to implement a new form of content by creating a library that does not make use of nodes, it is often more efficient to build on the existing well-tested, robust node API.
User records are maintained using this object type. Just as with comments and nodes, user data is stored in the database, and drawn out during processing. Information about a user is used for purposes such as authentication, determining preferences and permissions, and logging. Drupal 8 plugins are discoverable bits of the functionality centralized by a manager and that are used for certain tasks and features.
We will see more about plugins and provide many examples later in the book. A third extension point introduced in Drupal 8 is the event system. Events are primarily used in Drupal to intercept certain actions or flows in order to either stop or modify them. Many request to response tasks that were handled via hooks in the past are now being handled by dispatching events to check whether any modules are interested in, for example, delivering the response to the user.
It allows us to create services that can be injected in various places and receive themselves services as dependencies. They are then used for the heavy business logic of our functionality. Additionally, they are at times also used as an extension point because the service container is able to collect certain services that are marked as serving a specific purpose and use them automatically.
In other words, simply by defining a simple service, we can provide our own functionality or even change the existing logic. Now that we have listed the most important architectural pieces of Drupal, let's briefly see how these are used in delivering responses to the requests a user makes on a Drupal 8 website. To this end, we will analyze a very simplified example of a typical request as it is handled on a Drupal 8 website:.
In this context, as Drupal 8 module developers, we spend most of our times inside controllers and services, trying to figure out what we need to return to the page. We then rely on Drupal to transform our render array into a proper response to the user, but we can also return one ourselves directly.
Moreover, the theme system comes into play here, as well as the block system, because our content gets to be wrapped into a block that is placed in a region surrounded by other regions that contain blocks. However, if it sounds complicated now, don't worry, we will cover in detail all these aspects with examples, and it will become clear in no time. However, as a quick conclusion, we can see that events are mostly used but not only at the highest levels of a request, whereas plugins and hooks are mostly used at lower levels, within the process of calculating, building a page, or handling a specific business logic.
In the preceding section, we took a bird's-eye view of Drupal's architecture. Now, we will refine our perspective a bit.
We will walk through the major subsystems that Drupal 8 has to offer. It all starts with a route, doesn't it? Any interaction with a Drupal 8 website has its beginning in a user or system accessing a certain path or resource. This translates into a route, which maps that resource to a flow that hopefully returns a successful response back or at least a graceful failure. The Drupal 8 routing system is a major shift away from how it was in its previous versions. In Drupal 7 and earlier versions, the routing system was a very Drupal-specific thing a drupalism , if you will.
In this book, we will see how we can define our own route and map it to a controller that will render our page. We will cover a few of the more important route options and take a look at how we can control access to these routes. Progressively, entities have become a very powerful way of modeling data and content in Drupal.
The most famous type of entity has always been the Node, and it has been historically the cornerstone of content storage and display. In Drupal 8, the entire entity system has been revamped to make other entity types potentially just as important. They have been brought to the forefront and have been properly connected with other systems.
All entity types can have multiple bundles , which are different variations of the same entity type and can have different fields on them while sharing some fields. Drupal core still ships with the Node entity type, with a few bundles such as Basic Page and Article.
In addition, it comes with a few other entity types, such as User , Comment , and File. However, creating your own entity type in Drupal 8 has become much more standardized compared to Drupal 7 where contributed modules had to be brought into play. These are not the only types of entities we have in Drupal 8.
The examples mentioned previously are all content entity types. Drupal 8 introduced a new type, configuration entity types. The former are oriented toward content, but in reality, they are for anything that holds data that can be input into the database and is specific to that environment.
They are not used for storing configuration, though. Users and content are great examples, as they do not need to be usually deployable from one environment to other. The latter, on the other hand, are exportable items of the configuration of which there can be more than one. For example, a content entity bundle is a great example because there can be more than one bundle for a certain entity type; they have some metadata and information stored that can differ from bundle to bundle, and they need to be deployed on all environments.
That is, they are fundamental to the correct functioning of the site. Understanding the entity system is indispensable for doing development in Drupal 8 because it provides a powerful way of modeling custom data and content that goes past the traditional nodes that previously were used and is, in my opinion, too much way past their purpose. Now that we have an idea of what entities are, let's take a look at how data is actually stored on these entities.
I have alluded in the preceding section to how certain entity bundles can have various fields. This means that each entity type bundle can have any number of fields that are responsible for holding data. Additionally, each entity type itself can have fields for storing data.
Okay, but what? Let's break this down. There are two types of Fields in Drupal base fields and configurable fields. The former are fields that are defined in the code for each entity type you define or alter , whereas the latter are usually created and configured in the UI and attached to a bundle of that entity type and exported via configuration. So, essentially, both types can end up in the code to be deployed. Fields can also be of multiples types, depending on the data they store.
For example, you can have string or text fields, numeric fields, date fields, email fields, and so on. As developers, we can create our own field types if the existing ones are not good enough for our data. In this book, we will take a look at how we can define base fields on a certain entity type and create our own field type with its own data input widget and output formatter. Site builders can then use this field type on any entity type.
Any site needs some sort of navigation, right? Drupal not only maintains content, but also provides details about how the site itself is organized, that is, it structures how content is related.
The principle way that it does this is through the menu subsystem. The latter provides APIs to generate, retrieve, and modify elements that describe the site structure.
Put in common parlance, it handles the system's navigational menus. Menus are hierarchical, that is, they have a tree-like structure. A menu item can have multiple children, each of which may have their own children, and so on. In this way, we can use the menu system to structure our site into sections and subsections.
Listing of content and data is always an important capability content management systems covet; this is what Views provides in Drupal 8, and it does so well. If you've been building not even necessarily developing sites in previous versions of Drupal, you'll understand everything with this simple phrase--Views is now in Drupal core.
If you haven't, Views has always been a staple Drupal contributed module used on probably all Drupal installations to a certain extent and is an indispensable tool for site builders and even developers. The purpose of the Views module is to expose data and content in a way that allows the creation of configurable listings. It includes things such as filters, sorts, display options, and many other features.
As developers, we often find a need to write our own field or filter plugin to work with Views or expose data from our custom entities or external data sources. Views is a core Drupal 8 module tied to the general architecture and used for most list pages especially, admin pages provided by Drupal core.
Although it's a very site building-oriented tool, in this book, we will take a look at how we can create plugins that extend its capabilities to offer site builders even more. Ayen Green Publisher: J. Figure 8 —5. Adding a User reference field, with the three widget options shown Figure 8 —7. Author : Amanda L. When you want to return to your blog, visit www. You'll be met with a login screen, and then redirected to
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