Slides for the Introduction to Drupal Internals talk given at DrupalCamp Ashville in 2014. See the youTube video at https://www.youtube.com/watch?v=WWC7bhFZOEk This talk is intended to help non-programmers or programmers just starting to understand some of the basic structures that make up Drupal. OpenSource is great but often the documentation lacks. Knowing how to look around inside the code (even if you don't know how to code) can let you determine things that aren't documented.

1. Intro To Drupal Module Internals
Greg Monroe
Longsight, Inc.
Triangle Drupal Users Group

2. How will this help?
Drupal is user contributed. This means that
documentation is often lacking. The people
writing modules generally say “Read the
code”
Knowing some basics about Drupal module
internals, even if you can't program, will help
you use even the worst documented module.

3. Skills and Tools
●
A very basic knowledge of PhP (e.g. can kinda
follow the basic logic but may not be able to
write it)
●
A decent (plain) text editor ( e.g. Notepad++,
Text Edit, Gedit )
●
Optionally, you could find a more PhP friendly
editor that displays a function list and allows for
searching thru multiple file/directories. (SciTE,
Geany, NotePad++ with plugins, Eclipse,
Aptana, Zend…)

4. How modules work
●
Core finds them via modules admin page
●
Stores info about them in System DB table
●
Enabling module sets flag in System DB table, creates
required DB tables, does initial setup and registration
duties.
●
Main code for enabled modules loaded at page “boot”
by core.
●
Module code gets called via “hooks” by core and other
modules
●
Module Magic happens

5. What are Hooks
●
Drupal is based on hooks
●
Modules use them to extend Drupal and to
extend themselves.
●
Hooks are associated with key actions, e.g.
saving a node.
●
When a hook action happens, core or a
module with hooks calls all modules that
have implemented the hook for that action.

6. Some Hook Fundamentals
●
Hooks are documented like hook_name,
e.g. hook_block_info
●
Modules implement hooks as functions with
names that replace “hook” with the module
name.
E.g, the foo module would implement
hook_menu as foo_menu
●
Core hooks usually are in *.module files

7. POP QUIZ
If you read something like:
The foo module uses hook_menu to
do that”
What name will this hook use?

8. Answer:
This translates into a function with
the form:
foo_menu
E.g.: function foo_menu() {
Extra credit for knowing it might be in the
foo.module file.

9. Additional Reading
A good place to start learning about core
hooks is
http://api.drupal.org/
Search for “Hooks” for the main page or
search for hook_<name> for a specific
hook.

10. Useful Module Splunking Hooks
●
Hook_help
●
Hook_menu
●
Hook_block_info
●
Hook_theme
●
Hook_permision
●
Hook_views_api
Note: You can find full documentation on hook by googling:
“Drupal api hook_<name>”

11. Module Directory
➢ Files for a module will be under a common
directory.
➢ The name of this directory is the module's
“basename”. E.g., Organic group is “og”
and Node Gallery uses node_gallery
Note: Module base directories can exist
under other modules, e.g. og_views is
found in og/modules/og_views…

12. Module Files
Required:
<basename>.info
<basename>.module
Recommended:
README(.txt)
LICENSE(.txt)
<basename>.install
Naming Conventions:
*.inc – Include files loaded
as needed
*.pages.inc – code needed
for general pages
*.admin.inc – code needed
for admin pages
*.tpl.php – Override-able
theme template files
*.api.php – Documents the
hooks this module has

13. An Example of Module files
●
The Organic Group Module

14. Finding a Module
➢ Finding a module that is creating some page or block
from the displayed page is hard… and beyond this talk…
➢ If you know the “Human name”, e.g. Organic Groups, you
can find the base name from the
drupal.org/project/<base name> URL.
➢ Knowing this, see if you can download it from Drupal.org.
Looking at a module outside your web server is MUCH
safer.
➢ But if you think your site’s code is custom or you can’t
find the Drupal Project….

15. Where’s Wald..err..
the Module
Modules can live many places… but by convention they
generally live under one of three directories:
<drupal root>/modules (Core only!)
<drupal root>/sites/all/modules (for all sites)
<drupal root>/sites/default/modules
Note: In multisite setups, the sites/default part above may be
your host name, e.g. sites/www.my.com
Next check to see if a basename directory exists… if not, use a
file search tool to look for <basename>.info under these
directories.

16. The .info file
The module.info file
contains:
●
Basic description of
the module.
●
Dependencies
●
Object class files used
by this module.
●
CSS and Script files
●
Configure URL

17. The .Module File
The <Basename>.module file contains the core code
for the module and generally all the hooks we’re
interested in.

18. Finding Hooks
With the .module file in an editor:
➢ If your editor show functions, just look for the
_<hook name> postfix, e.g. “_menu”
➢ Search for “hook_<hook name>”, e.g.
“hook_menu”
➢ Search for <basename>_<hook name>, e.g.
“og_menu”
➢ Look for _<hook name>, e.g. “_menu”

19. Hook_Help
Notes:
Supplies text for Drupal
Advanced help system
Case statements
– URL help applies to
Return statements
- Help text

20. Hook_Menu
Notes:
Defines URLs (as menu
items or just pages) for
“pages” the module
creates
$items[…] statements
– URL of page
- %xxx indicate argument
substitution
‘title’ array key
- Menu/Page title
‘page callback’ array key
- function to create page
‘access callback’ array key
- function that determines
access

21. Hook_Block_Info
Notes:
- Defines blocks this
module adds
- ‘info’ array key is name
shown in block admin
display
The “block_view” hook
defines how the block
contents are created
The “block_configure”
hook (not shown)
defines any block
specific configuration
options

22. Hook_Theme
Notes:
‘<basename>_xxx’ keys
- These define the theme
“hooks” for this module
‘arguments’ key
- Defines the values passed
to the theme hook
‘template’ key
- Indicates this theme hook
is a .tpl.php template file
‘path’ key
- The directory the tpl.php
file is located.
Code for non-template hooks
will be in theme_<name>
functions.

23. Hook_Permission
Notes:
Defines any module specific
permissions.
Note that many modules use
PhP constants to define
permissions. So, look at
these to get the names used
in the permission settings
screens.

24. Hook_views_api
If you find this hook, you know that this module supports
views and might be supplying blocks and pages thru
code embedded views it installs.
The path option will indicate where the views related .inc
files will “live”. If you look thru these you will generally
find the names of views this module creates.
Other places to look for views information is in the
Module .info file.

25. Some “Advanced” Hooks
hook_node_* A set of hooks to modify the node save,
display and load options.
hook_user_* A set of hooks to modify user actions,
e.g. load, save, display, login, etc.
hook_form_alter Allows any Drupal form to be modified
by another module
hook_schema Defines database tables used by this
Module. This will be in the .install file.
hook_cron Defines any cron “jobs” a module needs
hook_*_alter Functions of this form generally are
using a hook to alter something that
core or a module provides.

26. Questions / More Info
➢ The book Pro Drupal Development is a good
reference
➢ Drupal API site has lots of docs on hook
➢ DrupalContrib.org has lots of docs on non-
core hooks
➢ Of course Drupal.org and general search
will help you find lots of good stuff.
Especially if you search for hook_<name>