1. Object Relational Mapping example
TopLink
Part of Oracle environment
Provides an Object/Relational Mapping Layer
References: pages from:
Oracle Toplink Unit of Work Primer
Patterns of enterprise application architecture
2003
Martin Fowler
Addison-Wesley
March 2004
R McFadyen

2. Patterns of enterprise application architecture
A book on enterprise application design
Layering
Domain/business logic
Web user interface
Object to relational mapping
Session state in a stateless environment
Distribution
March 2004
R McFadyen

3. Patterns of enterprise application architecture - Architecture
Two common elements to architecture:
Highest-level breakdown of a system into its parts
Decisions that are hard to change
page 2:
“The architectural pattern I like the most is that of layers”
“Most nontrivial enterprise applications use a layered architecture of some form”
March 2004
R McFadyen

4. Patterns of enterprise application architecture Unit of Work Pattern
Maintains a list of objects affected by a business transaction and coordinates the writing out of changes and the resolution of concurrency problems
Mentions 3 variations: caller registration, object registration, unit or work controller (e.g. Toplink)
March 2004
R McFadyen

5. unit of work controller variation:
Unit of Work Pattern
unit of work controller variation:
UoW makes a copy (clone)
Application works on the copy
UoW compares object and clone at commit time and issues necessary SQL to database …
March 2004
R McFadyen

6. Based on Primer pages 7, 8
Code shows how a Java program collaborates with Toplink to ensure a new object persists in the relational database
The application gets a Unit of Work.
Application creates a new Pet object, but the application works on a clone.
At commit time, Toplink issues the necessary SQL based on difference between clones and originals.
UnitOfWork uow = session.acquireUnitOfWork();
Pet pet new Pet();
Pet petClone = (Pet)uow.registerObject(pet);
petClone.setId(100);
petClone.setName(“Fluffy”):
petClone.setType(“Cat”);
uow.commit();
At commit time Toplink sends the following to the database
Insert into Pet (ID, Name, Type, Pet_Own_Id) Values (100, ‘Fluffy’ ,’Cat’ , Null)
March 2004
R McFadyen

7. Based on Primer pages 7, 8 :Client :session :UnitOfWork pet:Pet
acquireUnitOfWork()
new()
:UnitOfWork
new()
pet:Pet
registerObject(pet)
petClone:Pet
new()
petClone
setID(100)
setName(Fluffy)
setType(Cat)
commit()
At commit time, the UnitOfWork submits the SQL statement:
Insert into Pet (ID, Name, Type, Pet_Own_Id) Values (100, ‘Fluffy’ ,’Cat’ , Null)
March 2004
R McFadyen