What is iBATIS? - iBATIS in Action - page 35

Person

SELECT
ID as identifier,
FIRST_NAME as firstName,
LAST_NAME as lastName
MIDDLE_NAME as middleName,
HAIR_COLOR as hairColor,
HEIGHT as height,
WEIGHT as weight
FROM PERSON
WHERE ID = #identifier#

Person

identifier
firstName
lastName
middleName
hairColor
height
weight

ID
FIRST_NAME
LAST_NAME
MIDDLE_NAME
HAIR_COLOR
HEIGHT
WEIGHT

Figure 2.2 iBATIS SQL mapping

As you can see in figure 2.2, the mapping layer of i BATIS is actual SQL . i BATIS lets
you write your SQL . i BATIS takes care of mapping the parameters and results
between the class properties and the columns of the database table. For this rea-
son, and to eliminate any confusion around the various mapping approaches, the
i BATIS team often refers to the data mapper as a SQL mapper.

2.1 Mapping SQL

Any SQL statement can be viewed as a set of
inputs and outputs. The inputs are the param-
eters, typically found in the WHERE clause of the
SQL statement. The outputs are the columns
found in the SELECT clause. Figure 2.3 depicts
this idea.
The advantage to this approach is that the
SQL statement leaves a great deal of flexibility
in the hands of the developer. One can easily
manipulate the data to match the object
model without changing the underlying table
design. Furthermore, developers can actually introduce multiple tables or results
from built-in database functions or stored procedures. The full power of SQL is at
their fingertips.
i BATIS maps the inputs and outputs of the statement using a simple XML
descriptor file. Listing 2.1 shows an example of this.

Output Output

SELECT FIRST_NAME, LAST_NAME
FROM EMPLOYEE
WHERE EMPLOYEE_NUMBER=1234

Input

Figure 2.3 SQL can be viewed as inputs
and outputs.