Ch01 Introduction to Persistence in Java

8/8/2019 Ch01 Introduction to Persistence in Java

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Akin [email protected]

http://www.javaturk.orgDecember 2010
mailto:[email protected]://www.javaturk.org/http://www.javaturk.org/mailto:[email protected]


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Objects, Always

With the advent of the concept of object in 60s and 70s in firstSimula and then Smalltalk we started thinking in object-oriented terms

Then came Java in the mid of 90s and object-oriented thinkinginvaded our mind (even though we have a long way to make it

a new silver bullet in Software Engineering!)When we start talking about a new project we can not help

thinking in terms of objects

We can think of objects at different phases of the projects withdifferent concerns

We model requirements in terms of objects We design our solution in terms of objects

We implement the software in an object-oriented language such as Java

etc.

Well, at least we hope for this

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Storing Objects

But you know all good things eventually come to an end

How do you store your objects, make them persistent?

What are our options?Serializing objects to files or marshalling them to XML files

Persisting the objects to object-oriented databases

I wish we could

Persisting the objects to relational databases Most of the time this is the only option

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Why RDMSs?

It seems that storing our objects to a relational databasemanagement system (RDMS) will be our only choice forlonger times because

RDMS are ubiquitous

RDMS are very strong, skillful and mature in terms of ourenterprise needs

RDMS producers such as Oracle, IBM are very big, strongand well-known companies

Playing with objects stops when you stand in front of thehigh and fortified walls of relational databases and wemust obey their rules

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Object-Relational Mismatch

When you decide to store your objects into a RDMS youhave to answer many questions such as

How to represent each object in the database knowing thefact that your objects have complex compositional and

hierarchical relations among themselvesHow do you handle CRUD (Create-Read-Update-Delete)

operations for the objects?

How do you handle types differences between your codeand the database?

How do you minimize the database access for performanceand scalability purposes?

How about application-side caching?

Transactions, etc.

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Points of Mismatch

Aims and thus structures of object-oriented languages and

databases are totally different

So they are not congruent mainly on following very basic

issues:

Encapsulation

Types

Structure

IntegrityManipulation

Transaction

This is called object-relational mismatch

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Object-Relational Mapping ORM

Percentage of persistence effort for the objects in the projectsthat develop highly-transactional business software is high

Thus from the earlier times people started writing their own

framework or tool to automate object-to-table translation orbought one of a few, highly-expensive commercial tools

They aimed to make their persistence framework part of theirenterprise architecture so that in the long run the persistenceeffort in the projects can be smaller and more predictable

Process that manage object-relational mismatch and automatedesign-time mapping along with run-time CRUD operations arecalled Object-Relational Mapping or ORM

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ORM Tools

In 90s people tried to write its own ORM tools because

commercial ORM products were not many in number and

highly expensive.

We can divide history of commercial ORM products into

two different era:

Pre-Java ORM tools

Java ORM Tools

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Pre-Java ORM Tools

Some of the pre-Java ORM tools

Delphi

Rogue Wave DBTools.h++ (SourcePro DB now)

NeXT DBKit

Toplink for Smalltalk

IBM ObjectExtender

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Java ORM Tools: First Generation

JDBC 1.0 and 2.0

JavaBlend

Toplink for Java

EJB 1.0

VisualAge Persistence Builder

EJB 2.0

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Java ORM Tools: Second Generation

iBatis in 2001

Castor in 2002

Hibernate in 2002

JDO in 2002 through JSR-12

Java Persistence API (JPA) in 2006, through JSR-220

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Java Persistence API

Java Persistence API (JPA) 1.0 was released as part of EJB

3.0 in Java EE 5 in May, 2006

JSR-220: http://jcp.org/en/jsr/detail?id=220

Java Persistence API (JPA) 2.0 was released in December

2009 as part of Java EE 6

JSR-317: http://www.jcp.org/en/jsr/detail?id=317

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http://jcp.org/en/jsr/detail?id=220http://www.jcp.org/en/jsr/detail?id=317http://www.jcp.org/en/jsr/detail?id=317http://www.jcp.org/en/jsr/detail?id=317http://jcp.org/en/jsr/detail?id=220http://jcp.org/en/jsr/detail?id=220


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After JPA

With the advent of JPA, existing ORM products have

relased their JPA versions:

For example Hibernate and Toplink have two ORM products,

one with native API and the other one is the implementation

of JPA

Some of the JPA products in the market are

Hibernate Entity Manager

Toplink

EclipseLink (part of Toplink and donated by Oracle)

OpenJPA

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Popular JPA Pages

JSR-220: http://jcp.org/en/jsr/detail?id=220

JSR-317: http://www.jcp.org/en/jsr/detail?id=317

Main page at Oracle

http://www.oracle.com/technetwork/java/javaee/tech/persiste

nce-jsp-140049.html

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http://jcp.org/en/jsr/detail?id=220http://www.jcp.org/en/jsr/detail?id=317http://www.oracle.com/technetwork/java/javaee/tech/persistence-jsp-140049.htmlhttp://www.oracle.com/technetwork/java/javaee/tech/persistence-jsp-140049.htmlhttp://www.oracle.com/technetwork/java/javaee/tech/persistence-jsp-140049.htmlhttp://www.oracle.com/technetwork/java/javaee/tech/persistence-jsp-140049.htmlhttp://www.oracle.com/technetwork/java/javaee/tech/persistence-jsp-140049.htmlhttp://www.oracle.com/technetwork/java/javaee/tech/persistence-jsp-140049.htmlhttp://www.oracle.com/technetwork/java/javaee/tech/persistence-jsp-140049.htmlhttp://www.oracle.com/technetwork/java/javaee/tech/persistence-jsp-140049.htmlhttp://www.oracle.com/technetwork/java/javaee/tech/persistence-jsp-140049.htmlhttp://www.jcp.org/en/jsr/detail?id=317http://www.jcp.org/en/jsr/detail?id=317http://jcp.org/en/jsr/detail?id=220


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Why ORM?

Persistence efforts eat significant amount of resource in

software projects

ORM provides

Totally object-oriented approach

Concentration on business not plumbing code

Comprehensive solution to persistence layer

Higher productivity

Less code writtenPersistence made easy

Almost no coupling with database

High performance through object-caching

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Why Not ORM?

There are some down sides of ORMs:

Learning curve

Choosing the best implementation

Think about differences among the implementations

Poor performance possibility due to implementation choices

Possible cost of extra CPU, memory, database usage

May not suitable for everything:

Reporting, data migration, etc.Working with data that serves to legacy applications

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Approaches to ORM

How should one start ORM in a project?

Bottom-up

Top-down

Meet-in-the-middle

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Dont Forget!

And when using ORM tools dont forget about

Patterns and idioms

Best practices

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Ch01 Introduction to Persistence in Java

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