Drupal Interview Questions

Name and describe the five conceptual layers in a Drupal system.

The five layers in Drupal , starting from the bottom layer, are as follows:

1. Data (nodes, etc.). Before anything can be displayed on the site, it must be input as data.
2. Modules. Modules are functional plugins that are either part of the Drupal core or are contributed modules that build on Drupal’s core functionality.
3. Blocks and menus. Blocks can be used to present anything, so just about any piece of content on a Drupal site (other than main content, breadcrumbs, and primary/secondary menus) is usually a block. Blocks are an extensible core feature of Drupal with a simple API provided by the block module. Blocks are similar to “widgets” in content management systems, but are highly generalized. Menus are a collection of links (menu items) used to navigate a website. The Menu module provides an interface to control and customize the menu system that comes with Drupal. By default, new menu items are placed inside a built-in menu labeled Navigation, but administrators can also create custom menus.
4. User permissions. User permissions are defined for various roles and users are assigned to these roles in order to grant them the defined permissions.
5. Themes and templates. The top conceptual layer of the drupal architecture is the theme. This consists primarily of XHTML and CSS, with some PHP variables intermixed, so Drupal-generated content can go in the appropriate spots. Also included with each theme is a set of functions that can be used to override standard functions in the modules in order to provide complete control over how the modules generate their markup at output time. A theme may contain one or more templates, depending on the complexity of the site and the way it has been designed.

What is Drupal’s taxonomy system and what are some of its key features?

Drupal comes with a built in taxonomy system that allows for categorization of the nodes on a site.

The taxonomy system allows for arbitrary definition of terms, as well as arbitrary organization of those terms into vocabularies. There is no limit to the number of vocabularies that can be created, nor is there any limit to the number of terms that can be included in a vocabulary.

Describe the Field API that was introduced into core in Drupal 7.

The Field API allows custom data fields to be attached to Drupal entities and takes care of storing, loading, editing, and rendering field data. Any entity type (node, user, etc.) can use the Field API to make itself “fieldable” and thus allow fields to be attached to it. Other modules can provide a user interface for managing custom fields via a web browser as well as a wide and flexible variety of data type, form element, and display format capabilities.

The Field API defines two primary data structures, Field and Instance, and the concept of a Bundle. A Field defines a particular type of data that can be attached to entities. A Field Instance is a Field attached to a single Bundle. A Bundle is a set of fields that are treated as a group by the Field Attach API and is related to a single fieldable entity type.

What modules do you always recommend to your clients?

Before you ask this question, check out the Drupal module usage statistics page on drupal.org. Your candidate should be able to recommend a number of modules in the top 30.

Prompt your candidate to explain why they recommend each module. They should be able to give you a plausible-sounding explanation. If they recommend a particularly unpopular module, ask them how well it is supported.

Follow-up questions:

• Why do you recommend that module?
• How well is that module supported?
• Have there been any recent vulnerabilities with that module?

How does caching work in Drupal?

One of the common (mostly unfounded) complaints about Drupal has been, "Drupal is slow." You want to hire a developer who understands Drupal's built in caching system, and what its limitations are. For example, Drupal 6's block cache will not appreciably speed up the page if the user is logged in.

Ask your candidate to recommend some additional solutions to speed up Drupal's caching. These could include the Boost module, Varnish, Squid, Memcache or Pressflow. Ask if they've ever run into issues with Drupal's cache.

Follow-up questions:

• What else can you recommend to speed up Drupal?
• Have you ever run into issues with Drupal's cache?
• How did you solve them? Know More