Completing the Stack - Stripes...and Java Web Development is Fun Again - page 239

When the application starts, Hibernate generates and executes SQL
commands to create the database schema. The tables automatically
contain columns that correspond to the properties of the entity classes
as well as extra columns to manage the one-to-many/many-to-one rela-
tionships. The data is moved between the database and the model
classes, in both directions, without requiring us to write a single line of
SQL. And that's not all—Stripersist allows us to use our entity classes
directly, taking care of reading objects from the database for us. Let's
talk about that in more detail.
Stripersist Type Conversion and Formatting
Stripersist registers entity classes and does type conversion for them on
the fly. The type converter finds the @Id property on each @Entity class
(or @MappedSuperclass ) and uses it to convert a String to an entity class
by loading the corresponding object from the database. Stripersist also
creates formatters that do the opposite, which is to produce a String
from the model object's @Id .
We discussed writing type converters to load model objects from ID
parameters back in Section 5.4 , Using a Type Converter and Formatter
to Load Model Objects, on page 117 . With Stripersist, we don't need
to do this ourselves; Stripersist's type converter does it automatically.
Here's how it works. Say we have a Contact class with an @Id property
of type ID . Refer to Figure 12.3 , on the following page:
1. A request comes in with a someContact=5 parameter to be bound to
an action bean's someContact property of type Contact . Since Con-
tact has the @Entity annotation, Stripersist's TypeConverter<Entity>
is invoked.
2. The type converter finds the @Id property on the Contact class and
determines its type, ID .
3. Stripersist asks Stripes for a type converter for ID and calls its
convert ( ) method with the String parameter "5" .
4. The type converter returns the converted id value of type ID . This
works automatically if Stripes has a built-in type converter for the
ID type; otherwise, we need to provide our own.
5. The type converter then calls the JPA EntityManager 's find ( ) method
with the converted id object.
6. The EntityManager loads the Contact object from the database and
returns it.