Using the Transaction Script pattern - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 343

path directory or JAR file and are read by i BATIS on startup. In section 9.5, we will
look at how to configure i BATIS using Spring beans.
Even though DAO s written using i BATIS are much simpler than DAO s written
using JDBC , it is important to remember that maintaining the XML descriptor files
and SQL statements can be a lot of work. For example, let's imagine you need to
add a new field to an object. If you are using an ORM framework such as Hiber-
nate or JDO , which maps Java objects to the database schema, you just have to add
a single entry to an O/R mapping file. In comparison, if you are using i BATIS ,
which maps objects to SQL statements, you often need to change multiple state-
ments, including at least one SELECT statement, an INSERT statement, and an
UPDATE statement. Keeping multiple statements in sync can be both time-consum-
ing and error-prone. However, if you must execute SQL statements, then i BATIS is
an excellent way to do that.
For more detailed information about i BATIS and the Spring support classes,
see i BATIS in Action [Begin, forthcoming] and Spring in Action [Walls 2005]. Let's
now look at how to use i BATIS and Spring to implement a DAO and see some
examples of how to use the i BATIS and Spring API s.

9.4.2 Implementing a DAO method

Most DAO s are simple wrappers around the database access API , which in this
example is i BATIS . Each DAO method performs one or more database opera-
tions—executing a query, inserting rows, updating rows, deleting rows, or calling
a stored procedure—by executing i BATIS mapped statements.
Because we are using test-driven development, the task of implementing the
DAO s begins with writing a test. We could write a test that runs against the database,
but that would be slow and complicated. Instead, we will write tests that use mock
objects for the Spring and i BATIS API s. Once those pass, we will write tests that run
against the database.
We are going to use the findPendingOrder() method to illustrate how to imple-
ment a DAO method with Spring and i BATIS . This method, which is implemented
by the PendingOrderDAO , retrieves the pending order, its line items, its restaurant,
and its restaurant's menu items from the database and returns a PendingOrderDTO
containing this data.

Testing DAOs using mock objects
The first step in the process of implementing a DAO method is to write a mock
object test that verifies that the method executes the expected i BATIS statement
and returns the correct PendingOrderDTO . The findPendingOrder() method has to
execute three SQL statements: