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Apache Persistence Layers
 

Apache Persistence Layers

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Apache Persistence Layers Apache Persistence Layers Presentation Transcript

  • Cayenne, OpenJPA, iBatis Apache Persistence Layers ApacheCon EU 2008 Henning Schmiedehausen [email_address]
  • The O/R impedance mismatch Objects (Java Knowledge) RDBMS ?
  • In a nutshell…
    • “ Object-Relational mapping (O/RM),
    • is a programming technique that links
    • databases to object-oriented language
    • concepts, creating (in effect) a ‘virtual
    • object database’.”
    • – Wikipedia
  • Selection criterias
    • Data access (CRUD)
    • Developers knowledge
    • Database languages (SQL, DDL)
  • Can we stop here? I just need to query data for my (web) application. I could use the “industry standard”, right?
  • Yeah, right
    • JDO 1.0, 2.0, 2.1 ?
    • EJB 2 (Ieek!) or 3 ?
    • JPA ?
    • J2SE ? J2EE ?
    • And wait, there is more…
      • … Legacy code? Optimized SQL?
      • … Transparent or explicit persistence?
  • Meanwhile, outside Apache…
    • Hibernate
      • „ de facto standard“
      • (L)GPL licensed
      • driven by a single company
    • TopLink Essentials
      • JSR 220 Reference Implementation
      • CDDL + GPLv2
      • driven by a single company
  • Ok, ok, ok… So, why Apache?
  • Because we are at ApacheCon…
    • Apache Software License V2
      • Open Source
      • Commercial friendly
      • Non discriminatory
    • Strong community
      • Many contributors
      • Meritocracy
      • Commercial support available
  • Apache Persistence Layers
    • Apache Cayenne
    • Apache OpenJPA
    • Apache iBatis
    • not in this talk:
    • Apache Torque (http://db.apache.org/torque/)
    • Apache OJB (http://db.apache.org/ojb/)
  • Common Ground
    • JDBC, JTA, JNDI
    • Many popular DBs supported:
      • MySQL, PostgreSQL, Oracle, HSQLDB, Apache Derby
    • XML mapping definition files
    • 1:1, 1:n, m:n mappings
    • native and generated primary keys
  • Where are we?
    • Apache Cayenne
      • 2.0.4 (Oct 12th, 2007)
      • 3.0M3
    • Apache OpenJPA
      • 1.0.2 (Feb 18th, 2008)
      • 1.1.0-SNAPSHOT
    • Apache iBatis
      • 2.3.1 Beta (Mar 25th, 2008)
      • 3.0 in planning state
    • Swing GUI tool for modeling
    • Ant support, maven through ant tasks
    • concepts related to WebObjects EOF
  • Cayenne
    • Pros:
      • GUI modeler included
      • Good documentation
    • Cons:
      • all data objects inherit DataObject (3.0 will have POJO support)
      • no standards compliant API (3.0 will be JPA compliant)
    • implements JPA (JSR-220)
    • Ant support, maven through ant tasks
    • Command line tools included
    • based on Kodo, donated by BEA
    • Pros:
      • Standards based (JPA)
      • POJO support
      • Good documentation
    • Cons:
      • Some learning effort required
      • Only command line tools included
  • Example code
    • This talk can only scratch the concepts
    • Example code is available from my homepage, along with examples for other O/R tools:
    • http://henning.schmiedehausen.org/or-mappers/
    • http://svn.softwareforge.de/svn/opensource/talks/or-mappers/
  • A sample relation
  • Cayenne property
    • class People extends CayenneDataObject {
    • void setFirstName(String firstName ) { writeProperty ( "firstName" , firstName );
    • }
    • String getFirstName() { return (String) readProperty ( "firstName" );
    • }
  • Cayenne relation
    • class People extends CayenneDataObject {
    • void addToContacts(Contact contact ) { addToManyTarget ( "contacts" , contact , true);
    • }
    • void removeFromContacts(Contact contact ) { removeToManyTarget ( "contacts" , contact , true);
    • }
    • List getContacts() { return (List) readProperty ( "contacts" );
    • }
  • Cayenne mapping
    • <obj-entity name=&quot;People&quot; className=&quot; om.People &quot; dbEntityName=&quot; people &quot;>
    • <obj-attribute name=&quot; firstName &quot; type=&quot;java.lang.String&quot; db-attribute-path=&quot; people_firstname &quot;/>
    • </obj-entity>
    • <obj-relationship name=&quot;people&quot; source=&quot; Contact &quot; target=&quot; People &quot; db-relationship-path=&quot;people&quot;/>
    Class/DB Map Prop. / Col Map Obj Relation
  • OpenJPA property
    • @Entity @Table(name=&quot;people&quot;)
    • public class People {
    • private String firstName ;
    • @Basic @Column(name=&quot;people_firstname&quot;)
    • public String getFirstName() {
    • return firstName ;
    • }
    • public void setFirstName(String firstName) {
    • this. firstName = firstName;
    • }
    Class/DB Map Prop. / Col Map
  • OpenJPA relation
    • @Entity @Table(name=&quot;people&quot;)
    • public class People {
    • private Collection<Contact> contacts ;
    • @OneToMany(mappedBy = &quot;people&quot;, cascade={CascadeType.PERSIST, CascadeType.REMOVE})
    • public Collection<Contact> getContacts() {
    • return contacts ;
    • }
    • public void setContacts( Collection<Contact> contacts) {
    • this. contacts = contacts;
    • }
    Class/DB Map Obj Relation
  • Accessing the Mapper
    • Cayenne:
      • DataContext dataContext = DataContext.createDataContext();
    • OpenJPA:
      • EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory();
      • EntityManager em = entityManagerFactory .createEntityManager();
  • Retrieving an Object by PK
    • Cayenne:
      • People user = (People) DataObjectUtils .objectForPK( dataContext , People.class, 2);
    • OpenJPA:
      • People user = (People) em .find(People.class, 2L);
  • Changing an Object
    • Cayenne:
      • People people = retrieve();
      • people.setMember(true);
      • dataContext. commitChanges() ;
    • OpenJPA:
      • Transaction tx = em .getTransaction();
      • tx.begin() ;
      • People people = retrieve();
      • people.setMember(true);
      • tx.commit() ;
  • And Now… …for Something Completely Different
  • iBATIS
    • Data mapper framework
    • couples SQL queries to Java objects
    • Ant support, maven through ant tasks
    • Abator tool / Eclipse plugin
  • iBATIS
    • Pro:
      • fast, lightweight, unintrusive
      • Other Languages: Ruby, .NET
      • POJO support
      • Eclipse plugin
    • Cons:
      • SQL knowledge required
      • „ not mainstream“ concept
  • A mapped query
    • <select id=&quot; getPeople &quot; parameterClass=&quot;people&quot;
    • resultMap=&quot;peopleResult&quot; >
    • select * from people
    • <dynamic prepend=&quot;where&quot;>
    • <isNotNull prepend=&quot;and&quot; property=&quot;id&quot;>
    • people_id = #id#
    • </isNotNull>
    • </dynamic>
    • </select>
  • Query examples
    • Querying a single object
      • People select = new People ();
      • select.setId(2L);
      • People user = (People) sqlMap .queryForObject(&quot; getPeople &quot;, select);
    • Querying a list
      • List select = sqlMap .queryForList(&quot; getPeople &quot;, null);
  • Caveat
    • iBatis is not an O/R mapper, it is a data mapper!
    • calling retrieve() twice returns:
      • Cayenne, OpenJPA: The same object
      • iBatis: Two different objects
  • Which one to use?
    • This table is highly subjective! YMMV!
    … when standards compliance is a concern OpenJPA … if you need J2EE integration All of them … if your SQL is better than your Java / .NET iBATIS … if your Java is better than your SQL Cayenne, OpenJPA When What
  • Where to go from here?
    • http://henning.schmiedehausen.org/or-mappers/
      • Talk slides and Example code
    • O/R Mappers Homepages:
      • http://cayenne.apache.org/
      • http://openjpa.apache.org/
      • http://ibatis.apache.org/
      • Other ASF persistence mappers:
      • http://db.apache.org/torque /
      • http://db.apache.org/ojb /
  • ?
  • Thanks for your attention!