Like a read-only view object, an entity-based view object sends its SQL query straight to the database using the standard Java Database Connectivity (JDBC) API, and the database produces a result set. In contrast to its read-only counterpart, however, as the entity-based view object retrieves each row of the database result set, it partitions the row attributes based on which entity usage they relate to. This partitioning occurs by creating an entity object row of the appropriate type for each of the view object's entity usages, populating them with the relevant attributes retrieved by the query, and storing each of these entity rows in its respective entity cache. Then, rather than storing duplicate copies of the data, the view row simply points at the
entity row parts that comprise it.
The entity row that are brought into the cache using findByPrimaryKey() containes all attributes of the entity object. In contrast, an entity row created by partitioning rows from the View object query result contains values only for attributes that appear in the query. It does not include the complete set of attributes. This partially populated entity row represents an important runtime performance optimization.
