RDB/OO Patterns

It would be good if OO programs could interact with OO databases, but alas, relational databases have a 99% market share. This has led to many attempts to access them from OO languages. Design patterns for doing this have been developed, starting with "crossing chasms" and extending to Rails' ActiveRecord. Investigate the various approaches for marrying OO programs to relational databases, comparing them in terms of ease of programming, robustness, and efficiency.

Introduction

This article explores object-relation mapping (ORM), a programming technique that bridges object-oriented languages against relational databases, and compares them against more traditional approaches to database programming such as stored procedures and dynamic SQL. In the process, we examine basic design patterns for bridging this gap, and evaluate several popular ORM frameworks found in popular program languages in the process.

One of the primary problems that object-relational mapping (ORM) attempts to solve is that of transparent object persistence, which allows an object to outlive the process that created it. The state of an object can be stored to disk, and an object with the same state can be re-created in the future. This object data is typically internally stored in a relational database using SQL.

Unfortunately, relational databases lie at the core of any modern Enterprise application, and such tabular representation of SQL data is fundamentally different than the network of objects used in object-oriented applications. ORM allows us to interact with business objects directly in an object-oriented domain model, instead of having to work with rows and columns at the programming level.

Design Patterns

Comparison

In this section, we discuss the advantages and disadvantages of using object-relational mapping techniques in application development.

Ease of Programming

ORM applications are difficult to initially configure. But once configured, development in ORM is quite straight-forward.

Robustness

Using an ORM layer provides database independence.

Efficiency

Any good studies on this??

Implementations

ORM in Java

In recent years, Java has experienced a paradigm from complex heavy-weight frameworks such as Enterprise Java Beans to more light-weight agile frameworks that rely instead of simple Plain Old Java Objects (POJOs). This in turn, has increased the popularity of ORM for Java developers.

Indeed, Object-relational mapping is especially popular in the Java community, compared. for example to .NET developers. [1] Although a plethora of ORM frameworks exist for Java, among the most popular and widespread ORM layers today include Sun's JDO, Oracle's TopLink, Hibernate.

We begin with Java Data Objects (JDO), which by itself is not a framework, but a specification. The API is a standard interface-based Java model abstraction of persistence, developed under the auspices of the Java Community Process. Frameworks like Apache JDO then implement this specification. JDO aims to provide implementations for not only relational database, but also object database, and file systems.

http://www.kuro5hin.org/story/2006/3/11/1001/81803