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Drupal 6: Online Presentation of Data: Part 2 of 10Looking at Drupal's database
Drupal's built-in data presentation tools offer several ways for web designers to clearly and attractively package their data. In Drupal 6: Online Presentation of Data, Tom Geller explains how Drupal handles data so users can set up intelligent structures and implement them with Drupal's Content Construction Kit. Tom also shows how a data-driven web site can improve its interactivity by using geographic data to connect real-world addresses to maps. Exercise files accompany the course.
- Importing and manipulating data in Drupal
- Presenting date-formatted information in calendars
- Understanding Drupal's data-query interface, "Views"
- Improving view appearances with grid, list, and table formatting
- Importing, exporting, and cloning views
- Extending views with arguments and relationships
Looking at Drupal's database
Now we are ready to talk about Drupal itself. Keep in mind that Drupal essentially is just an attractive and flexible interface to a back end database. So it's worthwhile to take a look at that database to understand what exactly happens when you create, modify, and delete content in Drupal. This understanding will make Drupal administration a lot clearer overall and it opens up a world of possibilities if you are an advanced programmer or a database administrator.
We are working with a pretty clean installation of Drupal here. We are going to mess it up a little, so we'll be ready to roll it back to its previous state we are done. The Using the Exercise Files chapter of this course shows you how to save and restore a database, so be sure to watch that video if you decide to follow along and you end up making changes that you decide not to keep later. First, we have our site right here. Let's go and take a look at the database that's sitting behind it. To do so, we go up to phpMyAdmin and click on lynda, which is the name of the database we are using for this course. Each of the things you see here in this left column and here in the main part of the screen are individual tables. The names of these tables are fairly self-explanatory for the most part.
For example, let's take one of the simpler ones. User, we go down and we click where it says users here and we see the structure of the database. Each one of the rows here: name, pass, mail, and so forth is a field in that table. The mail field for example stores the email address for that user that the user gave when they created that account. If you click on the little icon to the left of that word user here, you get to browse the database. The other way to do that is by clicking on Browse up here, then you see the values that are in the database itself. Right now we have two users. When you create a Drupal site, user ID 0 is the anonymous user. It's sort of the placeholder for people who haven't actually logged into this site. User ID 1 is the super administrator who can do everything. From then on, everybody else is an authenticated user.
Information about these roles is stored in another table, here called role. In the roles table, we see the two roles that are setup in Drupal automatically. Role ID 1 is the anonymous user. Role ID 2 is an authenticated user. If we were to setup other roles later, they would be roles ID 3, 4, and so forth, and they would have whatever names we gave them. Then when we create users and assigned them to that role, those two would be connected so that a user would have a role ID.
Let's go back briefly to our users table however. And then let's go back to our site and actually create a user. To do so you would go to Administer > User management > Users > Add user. So under Username, we are going to make it tom, E-mail address email@example.com. Password, we'll just say password. Password of course we have to confirm, password. Scroll to the bottom. Active user, we are not going to notify them of it, but we create the account. Good, and it's all done. Now that we've created that user, let's see what actually happened in the database. So we go back to phpMyAdmin, and click again to browse the user's table. You'll notice there is tom, user ID 3. I think somewhere in the middle there I created another user and then deleted it, so instead of saying 2 it was It will keep increasing the user ID automatically, so you don't have to worry about it.
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But you can see there is our Password, it's encrypted so that someone who is looking at the database can't simply see it. The e-mail address, some flags on it to say whether or not they are an active user, when they last logged in and so forth. This example is going to be more complex, because when you create a node in Drupal, it actually affects many more tables. If you look along this left-hand side, you'll see node, node_access, node _common_statistics, etcetera, but let's go ahead and do that we'll see how it works.
So we go back to our site and Create content. This time I'm going to create a story and I'm going to say "Hello again, world!" The body is "Did you miss me?" and I'll scroll to the bottom and since this is a story, it will go to the front page automatically that's in Publishing options here, and Save. If we go back to our front page, we see there it is.
Now let's go back to our database and see exactly what happened. We click up here to go back to phpMyAdmin. Let's start with a node table. And there we see the first page we created earlier in this course, Hello, world! and there is our second one. It has a node ID, known as nId, a version ID, vId, and a lot of other information in here, but interestingly, it doesn't include the body of the node. That is actually referred to in another table, in node_revisions. If we go there, so you can see the Drupal actually keeps a complex set of relationships between node tables, and node revisions tables, and even the user tables. Here you can see which user created it, with the uId.
For those of you who want to get really deep into Drupal's database, I would like to suggest a few resources. The first one is a module called schema, and it's available at drupal.org/project/schema.
A schema describes how a database is built, and this module will show you how your particular database is created and interacts a little bit better while you are running your Drupal site.
The second module is called devel. Devel is for any kind of Drupal developer. It will show you the SQL commands that are being sent to and from the server, PHP messages, very useful if you are doing any sort of high-end Drupal development. So, that gives you an introduction to how Drupal handles data. I know this knowledge may seem arcane now, but it will help you in many ways beyond this course. For example, if your Drupal site is broken, you might be able to fix it by manipulating the database directly. And a thorough understanding of the database is essential to importing legacy data or to writing custom modules that use data in some way.
The functions of those 45 or so tables installed in Drupal by default, and the tables installed by dozens and dozens of common modules are a worthwhile study if you want to go further with your Drupal database knowledge. All it takes is phpMyAdmin, a Drupal installation and plenty of time.
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Tom Geller became involved in computers in 1976, playing "Hunt the Wumpus" on a hardwired terminal that spewed tractor-feed paper onto the floor. He later became a computer journalist, first providing shareware reviews to Apple's "eWorld" online service, and later serving as a reviews editor at MacWEEK. Since returning to freelance writing in 2006 after a five-year hiatus, his work has been published by Apple, Nature Magazine, the IEEE Computer Society, and Chemical Heritage Foundation. He lives in San Francisco. http://www.tomgeller.com
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