Drupal 7 Module Development

Chapter 6
In our case, we defined the bundle to use the type property so our artwork types
have a property called type that contains the machine name of the bundle. A
property called name for the human-friendly name of the bundle is a standard
convention but not strictly required, as is a human-readable description property.
The artwork_type_load() function is necessary for the menu placeholder to work,
but is also a very nice convenience function to have available as well. Generally it
is good practice to provide clean, flexible APIs to any system we develop, even if
we don't expect to use them. Odds are that we'll either find a use for them later or
someone else will think of a use we never expected.
Note that we are replacing dashes in a type name with underscores. That's because,
by convention, all Drupal paths use dashes in place of underscores but bundle names
need to use underscores, not dashes. When we use a type name in a URL we will
always use a dash, and so here we first fold the dash back to an underscore to make
sure we find the correct artwork type.
There is one other important detail here, and that is the drupal_static() function.
That function acts as a central collector for static PHP variables, that is, those that are
not technically global but should persist between calls to a function. They are quite
commonly used as a lightweight cache to avoid re-processing or refetching the same
data within the same page request, but that can in some cases lead to weird side
effects when the data being cached changes mid-request, such as when writing
unit tests.
The drupal_static() function acts as a central collector for such static variables.
By putting all such static variables in one place and giving the variable a name that
matches our function (that's what the __FUNCTION__ PHP constant means), we allow
systems that need to forcibly reset static caches without having a separate $reset
parameter for every part of the system.
Use the drupal_static() function to cheaply cache data
structures for one page request. Don't cache data that is too large
and too cheap to regenerate, though, as it does use up memory.
The entity controller
In the entity info hook we declared that we were going to use our own controller
class. That means we need to provide one. However, a controller class may not
always be small, and if it's only rarely used we don't want to parse that code on all
pages. Fortunately PHP provides a way to load class definitions on demand, and
Drupal makes it very easy to expose classes to PHP's autoloader.
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