mpoeschl 2002/06/24 08:07:16
Modified: xdocs user-guide.xml
Log:
fix doc generation error
Revision Changes Path
1.8 +27 -27 jakarta-turbine-torque/xdocs/user-guide.xml
Index: user-guide.xml
===================================================================
RCS file: /home/cvs/jakarta-turbine-torque/xdocs/user-guide.xml,v
retrieving revision 1.7
retrieving revision 1.8
diff -u -r1.7 -r1.8
--- user-guide.xml 23 Jun 2002 03:57:42 -0000 1.7
+++ user-guide.xml 24 Jun 2002 15:07:16 -0000 1.8
@@ -390,56 +390,56 @@
<p>
- Torque can handle object-oriented inheritance. There are generally
- considered to be 3 methods of object-relational mapping designs. Torque
- uses one of the fastest, mapping all objects in a class hierarchy to a
- single table. All attributes for every class in the hierarchy are stored
+ Torque can handle object-oriented inheritance. There are generally
+ considered to be 3 methods of object-relational mapping designs. Torque
+ uses one of the fastest, mapping all objects in a class hierarchy to a
+ single table. All attributes for every class in the hierarchy are stored
in the table. Consider an abstract ComputerComponent class that has Monitor
- and Keyboard subclasses. There would only be one table - both Monitor and
- Keyboard objects would be persisted to the same place. The table would
- consist of all ComputerComponent attributes, any unique Monitor attributes,
- and any unique Keyboard attributes. Keyboard table rows would have NULL for
+ and Keyboard subclasses. There would only be one table - both Monitor and
+ Keyboard objects would be persisted to the same place. The table would
+ consist of all ComputerComponent attributes, any unique Monitor attributes,
+ and any unique Keyboard attributes. Keyboard table rows would have NULL for
any unique Monitor data columns, and vice versa.
-
+
</p>
<p>
- The other fast method is to map each concrete class to a distinct
- table. Every object stores all attributes in a single row in the class table.
- An example would be that if we had a Kitchen class that inherited from Room,
+ The other fast method is to map each concrete class to a distinct
+ table. Every object stores all attributes in a single row in the class table.
+ An example would be that if we had a Kitchen class that inherited from Room,
two tables would be needed for storage. The Kitchen table would contain all
- of the columns of the Room table, plus any additional data columns needed to
+ of the columns of the Room table, plus any additional data columns needed to
describe the additional Kitchen attributes.
</p>
<p>
- The slowest, but most object-oriented method is to store each class in its
- own table. Only attributes that are added to a derived class are stored in
- its table. The persistence layer would need to join tables to read an object
- out of storage. Saving objects would be more complex, because objects will
- need to be distributed across multiple tables. For our Kitchen and Room
- example, there would also be two tables, Kitchen and Room, but the Kitchen
- table would only contain those attributes which weren't part of the Room
+ The slowest, but most object-oriented method is to store each class in its
+ own table. Only attributes that are added to a derived class are stored in
+ its table. The persistence layer would need to join tables to read an object
+ out of storage. Saving objects would be more complex, because objects will
+ need to be distributed across multiple tables. For our Kitchen and Room
+ example, there would also be two tables, Kitchen and Room, but the Kitchen
+ table would only contain those attributes which weren't part of the Room
class.
</p>
<p>
- One of the advantages of the first method (the one Torque uses) is that it
- does not require joins like the third method described above. Another
- advantage is that the data model is easier to maintain than the second
+ One of the advantages of the first method (the one Torque uses) is that it
+ does not require joins like the third method described above. Another
+ advantage is that the data model is easier to maintain than the second
method. It falls short in modelling a class hierarchy where the related
classes have a non intersecting collection of attributes, as in this case
a row in the table will have several null columns.
-
+
</p>
<p>
- For more information, visit Scott Ambler's excellent web site,
- <a href="http://www.ambysoft.com/";>AmbySoft.com</A>, where he discusses
+ For more information, visit Scott Ambler's excellent web site,
+ <a href="http://www.ambysoft.com/";>AmbySoft.com</a>, where he discusses
object mapping to relational databases.
-
+
</p>
</section>
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