Drupal 7 Module Development

Chapter 7
Although an advanced topic, pluggable field storage is one of
the major new features of the Field API and is another option for
handling remote data sources in Drupal.
Creating our new field type
Field types are defined by modules, so let's start by creating a new module called
dimfield.module. Its info file is as follows:
name = Dimensions field
description = A Field offering height, width, and depth
package = Drupal 7 Development
core = 7.x
files[] = dimfield.module
Declaring the field
Now in dimfield.module, we need to implement hook_field_info(), which is
how we tell Drupal about our new field type.
function dimfield_field_info() {
return array(
'dimensions' => array(
'label' => t('Dimensions'),
'description' => t(
'This field stores a height and width, and depth.'),
'settings' => array('num_dimensions' => 2),
'instance_settings' => array(
'max_height' => 0,
'max_width' => 0,
'max_depth' => 0,
),
'default_widget' => 'dimfield_combined',
'default_formatter' => 'dimfield_default',
),
);
}
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