Java Persistence API Framework_v2

8/13/2019 Java Persistence API Framework_v2

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Persistence Framework

Persistenceframework


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2

Objectives

Understanding Database Encapsulation Advantages and Disadvantages of Database

Encapsulation Implementation Strategies Persistence Framework JPA API Best Practices


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Encapsulation

!e term encapsulationis often usedinterc!angeabl" wit! information !iding# it ist!e !iding of design decisionsin a computerprogram t!at are most likel" to c!ange# t!usprotecting ot!er parts of t!e program fromc!ange if t!e design decision is c!anged$

!e protection involves providing a stableinterface$ In modern programming

languages# t!e principle of information !idingmanifests itself in a number of wa"s#including encapsulation %given t!eseparation of concerns& and pol"morp!ism$


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Encapsulation on Database

!e implication of encapsulation is t!at we can buildcomponents and c!ange it later wit!out affect ot!ercomponents wit!in t!e s"stem as long as t!e interfaceto t!at component did not c!ange$

Database is t!e place for information storage# we canalso !ave various encapsulation arc!itectures# andimplementation strategies so t!at we can decouple t!ecode wit! t!e database s"stem including t!eir p!"sicalsc!emas from business code $

a t"pical arc!itectural la"ering strateg" for buildingbusiness applications w!ic! includes a databaseencapsulation la"er %also known as a persistence la"eror simpl" a data la"er&$


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Starting from '(((# developers figured out#t!at accessing relational databases using)ust*directl" JDB+ is a rat!er dirt"*ugl" wa"$

!e differences in ob)ect,oriented design andrelational databases got tooobvious$

a number of pro)ects including opensource!ave been set up to solve t!is problem in amore elegant wa"

-ibernate# +astor# +a"enne# .JB#or/ue#D.DS#oplink# iBatis# AD. and etc

ob)ect,oriented databases were at t!at timealread" more or less p!ased out$

A Brief History of Persistence
http://www.hibernate.org/http://www.castor.org/http://incubator.apache.org/cayenne/http://db.apache.org/ojb/http://db.apache.org/torque/http://www.enhydra.org/tech/dods/index.htmlhttp://www.oracle.com/technology/products/ias/toplink/index.htmlhttp://ibatis.apache.org/http://ibatis.apache.org/http://www.oracle.com/technology/products/ias/toplink/index.htmlhttp://www.enhydra.org/tech/dods/index.htmlhttp://db.apache.org/torque/http://db.apache.org/ojb/http://incubator.apache.org/cayenne/http://www.castor.org/http://www.hibernate.org/


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Database Encapsulation Befits

It reduces t!e coupling of ob)ect and databaseso t!at increasing abilit" to evolve eit!er one$

It implements all data,related code in oneplace$ It make t!e programmers )ob easier$

It gives "ou a common place to implementdata,oriented business rules$

It allow to takes advantage of specificdatabase features# increasing applicationperformance

It allows application programmers to focus ont!e business problem and DBA%s& can focus ont!e database$ %separation of responsibilities&


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Database encapsulation disadvantages

!ere are potentiall" several disadvantages ofdatabase encapsulation0

Increase t!e Investment$

!e" often re/uire reasonabl" clean1apping$

Provide not enoug! control over databaseaccess$



Implementation Strategies ForDatabase Enca sulation La ers

Just 2uer"0 business ob)ects access datasources directl" b" submitting Structure2uer" 3anguage %S23& or .b)ect 2uer"3anguage %.23& code to t!e database

Data access ob)ects%DA. it encapsulate t!edatabase access logic re/uired of businessob)ects# It also !ave industr",standardapproac!es suc! as Java Data .b)ect %JD.&

and Active4 Data .b)ect %AD.&$



Implementation Strategies ForDatabase Enca sulation La ers

Persistence framework*tools0 It encapsulatesdatabase access from business ob)ects$ Insteadof writing code to implement t!e Databaseaccess logic # it re/uire to define meta data t!at

represents t!e mappings$ Data Service0 It is an operation offered b" a

component entit" or application t!at can beinvoked b" ot!er entities# for e5ample$

> +ommon .b)ect 6e/uest Broker Arc!itecture %+.6BA&> +ustomer Information +ontrol S"stem %+I+S& ransaction> Distributed +omponent .b)ect 1odel %D+.1&> Electronic data interc!ange %EDI&> Stored procedures

> 7eb Services



Wat is te issue!Some applications ma" not take advantage oft!e encapsulation la"er%s& and some ma" not#t!e" !ave to access data directl" to t!eDatabase $

legac" applications cannot access*not allow tot!e database encapsulation $

rework some of "our legac" applications to uset!e database encapsulation la"er cannot or

will not performed*wanted$!ere are some tec!nologies# suc! as a bulk

load facilit" or a reporting framework# t!atre/uire direct access to t!e database sc!ema$



Note

!ere are still !ave values to implementdatabase encapsulation because we

can reduce coupling of ob)ect and DBand t!erefore reducing developmentcosts and maintenance effort$



General Persistence Framework features

, 7rite S23automaticall"

, +reate Joins for -as,one 6elations!ips

, Aggregate Sub/ueries

, Support Paging

, Allow for 8ersioning

, +ascading operation

, -andle +olumnAliases

, Support In!eritance

, 8alue .b)ectssupport

, +ac!ing mec!anism



"ava Persistence #e$uirements

Simplification of t!e persistence model> Elimination of deplo"ment descriptor

3ig!t,weig!t persistence model> In terms of programming and deplo"ment model as

well as runtime performance

estabilit" outside of t!e containers> +reate test clients t!at would use entities in a non,

managed environment

Domain modelling t!roug! in!eritance andpol"morp!ism

.b)ect*6elational %.*6& mapping

E5tensive uer in a abilities



JPA Primary Features

P.J.,based persistence model Plain .ld Java .b)ects

Supports traditional .,. modelling concepts

In!eritance# pol"morp!ism# encapsulation# etc$ Standard abstract relational /uer" language

Java Persistence 2uer" 3anguage Standard .*6 mapping metadata

Using Java SE 9 Annotations and*or 413 Portabilit" across providers %implementations&

oplink# -ibernate# :odo# .penJPA# Eclipse3ink



Java Persistence P! "JP# Java Persistence API %JPA& provides P.J. %Plain .ld Java .b)ect&

standard and ob)ect relational mapping %.6 mapping& for datapersistence among applications$

Persistence# w!ic! deals wit! storing and retrieving of applicationdata# can now be programmed wit! Java Persistence API starting

from EJB ;$( as a result of JS6 ''($ Java Persistence API !as borrowed man" of t!e concepts and

standards from leading persistence frameworks like oplink %from.racle& and -ibernate %from JBoss&$ .ne of t!e great benefits of JPAis t!at it is an independent API and can nicel" integrate wit! J'EEas well as J'SE applications$



Principles on ow to use "P%

!e JPA is a specification# JPA providerimplementations !ave to keep t!ePortabilit"$ Even for t!e provider,specificfunctionalit"# t!e" s!ould be easil" toidentif" and isolated$

JPA,based code s!ould usuall" work inbot! Java SE and Java EE environment$

JPA code s!ould be portable acrossdifferent datasources$ If database,specific features must be used# t!e"s!ould be isolated in configuration files

rat!er t!an tainting t!e code$



Principles on ow to use "P%

Self,e5planator" code and annotationsare preferable to comments t!at arenecessar" to e5plain convoluted code$

!e best practices generall" re/uire ver"little e5tra effort to implement andprovide long,term maintenance benefitsat little or no cost in initial development

time Service Provider Interface %SPI& for

container*persistence providerplugabilit"$



"ava Persistence %PI &est Practices

Standard SQL for Database if required

Effectively Use Database-SpecificFeatures

Select a suitable Layer for PA !odeLayer

Favor Self-Describin" !ode over#etadata and !o$$ents

Define %a$in" !onventions to &ave a#ore-'eadable !ode

!onsider usin" Sprin" fra$e(or) toPA



"ava Persistence %PI &est Practices

!arefully !onsider and Select a#etadata !onfi"uration Strate"y

Favor !onventions over E*ceptions

Access Fields 'at&er +&an Properties,#ore freedo$

Favor .E$bedded/d for !o$posite0eys

Use 1nly E*act Datatypes for Pri$ary0eys,usin" inte"er

Usin" Standard PA !ode

Effectively Use /$ple$entation-Specific

Features



Java Persistence P! Best Practices

6eplacing an eager loading strateg" wit!a la



FuturesJPA 2.0. The focus is on refining, fixing,and improving portability. Some possiblene features of JPA 2.0!

"etter validation support, e.g.

#$ength%&', #(ax%2' )mproved JP*$ support

+riteria AP) support

Toplin and -iberate already have this.

The -ash(ap lie hints %e.g. logging,caching' to be standardised

toplin.logging.level

toplin.cache.type.default


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JP $%& proposed features1ore fle5ible modeling

Embeddable class support , embed a class into anot!erclass wit!out mapping t!at class directl" to a table$Instead it=s stored >embedded> inside anot!er class as acolumn in t!e table$

.rdered 3ists ? !e ordering applied to a /uer" to bepersisted in t!e database$ From t!e database perspective#!ardwiring ordering in t!e database is done b" defining aninde5 column$

Access "pe , t!e process of defining w!et!er t!e provider

uses fields or properties to access t!e elements of a class$+urrentl" a single access t"pe applies to complete entit"!ierarc!"$ !e proposed c!ange is to allow "ou to specif"t!is on a per,class basis#

@Access"pe%P6.PE6&annotation on an entit" class$


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JP $%& proposed features

E5panded .*6 1appping Functionalit" Unidrectional one,to,man"

relations!ips using foreign ke"ou reall" don=t want bot! ends of

one,to,man" relations!ip to !ave toknow about eac! ot!er$ oda" "ou!ave to use a )oin table$ !is c!angewould allow "ou to specif" t!erelations!ip on one side onl"$


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2ueries Some current limitations0

SE3E+ clause too constrained$ .nl" supports aggregatefunctions

Some unnecessar" restrictions on parameter usage , w!at

about collections 2ueries are alwa"s pol"morp!ic

D"namic /ueries currentl" entail string construction$ !is isburdensome on t!e appaction to build t!is$ +riteria APIs allow>node,wise> /uer" construction$

+riteria2uer" c/ C em$create+riteria2uer"%+ustomer$class&

$add%6estrictions$e/%>status># >preferred>&

$add%6estrictions$e/%># >('(>&

!ere are alread" e5isting criteria APIs and e5pressionlanguage APIs available , -ibernate# .JB# +a"enne# op3ink#etc$


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JP $%& proposed features Standardi


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JP $%& proposed features E5tended persistence conte5t

Allow entities to remain managed across multiple serial transactions$Application,managed is alwa"s e5tended$ It is up to t!e developer tomanage t!e lifec"cle of t!e persistence conte5t$ It is also up to t!eapplication to manage t!e association between a JA transaction andpersistence conte5t$

.ne wa" to solve t!e issue is made t!e Entit"1anager detects it is in atransaction and registers wit! JA for notifications$ But t!eEntit"1anager is not alwa"s created at t!e beginning of a transaction#or "ou ma" !ave multiple active transactions# so t!e ot!er wa" to dot!is is to register t!e Entit"1anager wit! a transaction usingem$)oinransaction%&$ +ontainer,managed transactions is for Java EEenvironments# and provides a muc! easier solution$

!ere is an open issue wit! conversational state# passivation andclustering$ Basicall" it is not well defined w!at !appens w!enconversational state contains an Entit"1anager and gets passivatedand reconstituted# particularl" on anot!er instance of a cluster$ JPA '$(will tr" to fi5 t!is$


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8alidation JS6 ;(; on Bean 8alidation defines a

metadata model and API for validation# for

general use in SE and EE$ !e" want toleverage t!is in JPA but it depends on timing$Some e5ample validations include

@6e/uired# @3engt!%ma5C9& @1a5%'( etc$!e" are also looking at supporting user,definedvalidation# e$g$ @Ade/uatel"+ompensated$7!en "ou define t!ese validation annotations#t!e provider can automaticall" c!eck t!at t!eseconstraints are met$


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J'( )*+ and (!

JS6 ;0 Java1 Persistence '$( is now inProposed Final Draft !ttp0**www$)cp$org*en*)sr*detailidC;

Eclipse Persistence Services Pro)ect%Eclipse3ink& is going to be t!e referenceimplementation of JPA '$($ !ttp0**www$eclipse$org*eclipselink*
http://www.jcp.org/en/jsr/detail?id=317http://www.jcp.org/en/jsr/detail?id=317


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#esources

Klassfis! persistence !omepage

!ttps0**glassfis!$dev$)ava$net*)avaee9*persistence

Persistence support page

!ttps0**glassfis!$dev$)ava$net*)avaee9*persistence*entit"persistence,support$!tml

Blog on using persistence in 7eb applications

!ttp0**weblogs$)ava$net*blog*ss';*arc!ive*'((9

*'*usingL)avaLpers$!tml Blog on sc!ema generation

!ttp0**blogs$sun$com*roller*page*)ava'dbInKlassFis!MautomaticLtableLgenerationLfeatureLin

Java Persistence API Framework_v2

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