Drupal 7 Module Development

Creating New Fields
Always use EntityFieldQuery when selectively searching for entities.
Never try to query the database directly, as there is no guarantee that
there is a relational database involved.
Let's start with simply showing the five most recently created artworks:
function artwork_page_list_recent() {
$content = array();
$query = new EntityFieldQuery();
$query
->entityCondition('entity_type', 'artwork')
->propertyOrderBy('created', 'DESC')
->range(0, 5);
$result = $query->execute();
$artworks = artwork_load_multiple(array_keys($result['artwork']));
foreach ($artworks as $artwork) {
$content[] = artwork_page_view($artwork, 'teaser');
}
}
return $content;
We start by creating a new query object. We then call methods on it, to filter by
"entity type is 'artwork'", and then "order by the 'created' property, newest first"
(that is, descending order). The range() method, just like DB queries, takes the
start position as its first parameter and the count as its second.
If we assume an SQL database, the resulting SQL will look something like
the following:
SELECT artwork.aid AS entity_id, artwork.vid AS revision_id, artwork.
type AS bundle, 'artwork' AS entity_type
FROM
artwork artwork
ORDER BY artwork.created DESC
LIMIT 5 OFFSET 0
The advantage here is that, should the author of the artwork module change the
table structure on us, or if artworks were stored in a non-SQL data store, the SQL
query above would break horribly but the EntityFieldQuery would continue to work
because Drupal builds it dynamically based on what we're searching for.
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