Drupal 7 Module Development

Creating New Fields
In the last chapter we saw how to define new entities. The main advantage of
defining our content as an entity, of course, was to make it accessible to the Field
API. In this chapter, we will look at how fields work and how to define new fields
to attach to either our own entities or to those already defined, such as nodes.
Along the way we'll cover:
• What Field API is and what it does
• How to use magic callbacks
• Using fields to store data
• Using widgets to hook fields into the Form API
• Using formatters to control the display of fields
When we're done, you should have an understanding of how all the key pieces of
Drupal's main data handling system fit together and how to leverage them best.
Our goal: a "dimensions" field
In the last chapter, we created a new type of entity called Artwork. As a fieldable
entity, we can attach any field we want to it. Sometimes though, we'll still need to
create our own field types. That may happen if we want to treat a given piece of
information atomically rather than building it up out of smaller parts. There are
many reasons why that could be the case. They are as follows:
1. We want to conceptually treat that piece of data as a single chunk with
its own meaning rather than as a series of chunks that together we know
has meaning.
2. We have complex data but want to have multiple instances of that data on a
single entity.