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• How to iterate JPA collections in Google App engine

  - by palto

  Hi I use Google App Engine with datanucleus and JPA. I'm having a real hard time grasping how I'm supposed to read stuff from data store and pass it to JSP. If I load a list of POJOs with entitymanager and pass it to JSP, it crashes to org.datanucleus.exceptions.NucleusUserException: Object Manager has been closed. I understand why this is happening. Obviously because I fetch the list, close the entity manager and pass it to JSP, at which point it will fail because the list is lazy. How do I make the list NOT lazy without resorting to hacks like calling size() or something like that? Here is what I'm trying to do: @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { req.setAttribute("parties", getParties()); RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("/WEB-INF/parties.jsp"); dispatcher.forward(req, resp); } private List<Party> getParties(){ EntityManager em = entityManagerProvider.get(); try{ Query query = em.createQuery("SELECT p FROM Party p"); return query.getResultList(); }finally{ em.close(); } }

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• JPA entitylisteners and @embeddable

  - by seanizer

  I have a class hierarchy of JPA entities that all inherit from a BaseEntity class: @MappedSuperclass @EntityListeners( { ValidatorListener.class }) public abstract class BaseEntity implements Serializable { // other stuff } I want all entities that implement a given interface to be validated automatically on persist and/or update. Here's what I've got. My ValidatorListener: public class ValidatorListener { private enum Type { PERSIST, UPDATE } @PrePersist public void checkPersist(final Object entity) { if (entity instanceof Validateable) { this.check((Validateable) entity, Type.PERSIST); } } @PreUpdate public void checkUpdate(final Object entity) { if (entity instanceof Validateable) { this.check((Validateable) entity, Type.UPDATE); } } private void check(final Validateable entity, final Type persist) { switch (persist) { case PERSIST: if (entity instanceof Persist) { ((Persist) entity).persist(); } if (entity instanceof PersistOrUpdate) { ((PersistOrUpdate) entity).persistOrUpdate(); } break; case UPDATE: if (entity instanceof Update) { ((Update) entity).update(); } if (entity instanceof PersistOrUpdate) { ((PersistOrUpdate) entity).persistOrUpdate(); } break; default: break; } } } and here's my Validateable interface that it checks against (the outer interface is just a marker, the inner contain the methods): public interface Validateable { interface Persist extends Validateable { void persist(); } interface PersistOrUpdate extends Validateable { void persistOrUpdate(); } interface Update extends Validateable { void update(); } } All of this works, however I would like to extend this behavior to Embeddable classes. I know two solutions: call the validation method of the embeddable object manually from the entity validation method: public void persistOrUpdate(){ // validate my own properties first // then manually validate the embeddable property: myEmbeddable.persistOrUpdate(); // this works but I'd like something that I don't have to call manually } use reflection, checking all properties to see if their type is of one of their interface types. This would work, but it's not pretty. Is there a more elegant solution?

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• Storing a jpa entity where only the timestamp changes results in updates rather than inserts (desire

  - by David Schlenk

  I have a JPA entity that stores a fk id, a boolean and a timestamp: @Entity public class ChannelInUse implements Serializable { @Id @GeneratedValue private Long id; @ManyToOne @JoinColumn(nullable = false) private Channel channel; private boolean inUse = false; @Temporal(TemporalType.TIMESTAMP) private Date inUseAt = new Date(); ... } I want every new instance of this entity to result in a new row in the table. For whatever reason no matter what I do it always results in the row getting updated with a new timestamp value rather than creating a new row. Even tried to just use a native query to run an insert but channel's ID wasn't populated yet so I gave up on that. I've tried using an embedded id class consisting of channel.getId and inUseAt. My equals and hashcode for are: public boolean equals(Object obj){ if(this == obj) return true; if(!(obj instanceof ChannelInUse)) return false; ChannelInUse ciu = (ChannelInUse) obj; return ( (this.inUseAt == null ? ciu.inUseAt == null : this.inUseAt.equals(ciu.inUseAt)) && (this.inUse == ciu.inUse) && (this.channel == null ? ciu.channel == null : this.channel.equals(ciu.channel)) ); } /** * hashcode generated from at, channel and inUse properties. */ public int hashCode(){ int hash = 1; hash = hash * 31 + (this.inUseAt == null ? 0 : this.inUseAt.hashCode()); hash = hash * 31 + (this.channel == null ? 0 : this.channel.hashCode()); if(inUse) hash = hash * 31 + 1; else hash = hash * 31 + 0; return hash; } } I've tried using hibernate's Entity annotation with mutable=false. I'm probably just not understanding what makes an entity unique or something. Hit the google pretty hard but can't figure this one out.

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• Loading child entities with JPA on Google App Engine

  - by Phil H

  I am not able to get child entities to load once they are persisted on Google App Engine. I am certain that they are saving because I can see them in the datastore. For example if I have the following two entities. public class Parent implements Serializable{ @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String key; @OneToMany(cascade=CascadeType.ALL) private List<Child> children = new ArrayList<Child>(); //getters and setters } public class Child implements Serializable{ @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String key; private String name; @ManyToOne private Parent parent; //getters and setters } I can save the parent and a child just fine using the following: Parent parent = new Parent(); Child child = new Child(); child.setName("Child Object"); parent.getChildren().add(child); em.persist(parent); However when I try to load the parent and then try to access the children (I know GAE lazy loads) I do not get the child records. //parent already successfully loaded parent.getChildren.size(); // this returns 0 I've looked at tutorial after tutorial and nothing has worked so far. I'm using version 1.3.3.1 of the SDK. I've seen the problem mentioned on various blogs and even the App Engine forums but the answer is always JDO related. Am I doing something wrong or has anyone else had this problem and solved it for JPA?

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• JSP JPA Form: how to insert value in a path variable

  - by kajarigd

  I have the following code snippet in a jsp file: <hr> <form:form commandName="newTicketSale" id="reg" action="transactionResult.htm"> <h3>Buy Movie Tickets:</h3> <form:label path="movieName">Movie Name:</form:label> <form:input path="movieName" /> <form:errors class="invalid" path="movieName" /> <form:label path="ticketPrice">Ticket Price:</form:label> <form:input path="ticketPrice" /> <form:errors class="invalid" path="ticketPrice" /> <input type="submit"> <br><br> </form:form> I am using JPA tags in this jsp. Now, in the commandName "newTicketSale" there is another parameter called userId. In the jsp file itself I need to insert value ${name} in userId, so that in the Controller file when I am doing @Valid @ModelAttribute("newTicketSale") MovieTicket newTicket I can retrieve the value ${name} when I am doing newTicket.getUserId(). I don't know how to do this. Please help! Thanks in advance!

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• JPA - Real primary key generated ID for references

  - by Val

  I have ~10 classes, each of them, have composite key, consist of 2-4 values. 1 of the classes is a main one (let's call it "Center") and related to other as one-to-one or one-to-many. Thinking about correct way of describing this in JPA I think I need to describe all the primary keys using @Embedded / @PrimaryKey annotations. Question #1: My concern is - does it mean that on the database level I will have # of additional columns in each table referring to the "Center" equal to number of column in "Center" PK? If yes, is it possible to avoid it by using some artificial unique key for references? Could you please give an idea how real PK and the artificial one needs to be described in this case? Note: The reason why I would like to keep the real PK and not just use the unique id as PK is - my application have some data loading functionality from external data sources and sometimes they may return records which I already have in local database. If unique ID will be used as PK - for new records I won't be able to do data update, since the unique ID will not be available for just downloaded ones. At the same time it is normal case scenario for application and it just need to update of insert new records depends on if the real composite primary key matches. Question #2: All of the 10 classes have common field "date" which I described in an abstract class which each of them extends. The "date" itself is never a key, but it always a part of composite key for each class. Composite key is different for each class. To be able to use this field as a part of PK should I describe it in each class or is there any way to use it as is? I experimented with @Embedded and @PrimaryKey annotations and always got an error that eclipselink can't find field described in an abstract class. Thank you in advance! PS. I'm using latest version of eclipselink & H2 database.

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• Hibernate JPA Caching Problem, Please help!

  - by Sameer Malhotra

  Ok, Here is my problem. I have a table named Master_Info_tbl. Its a lookup table: Here is the code for the table: @Entity @Table(name="MASTER_INFO_T") public class CodeValue implements java.io.Serializable { private static final long serialVersionUID = -3732397626260983394L; private Integer objectid; private String codetype; private String code; private String shortdesc; private String longdesc; private Integer dptid; private Integer sequen; private Timestamp begindate; private Timestamp enddate; private String username; private Timestamp rowlastchange; //getter Setter methods I have a service layer which calls the method       service.findbycodeType("Code1");   same way this table is queried for the other code types as well e.g. code2, code3 and so on till code10 which gets the result set from the same table and is shown into the drop down of the jsp pages since these drop downs are in 90% of the pages I am thinking to cache them globally. Any idea how to achieve this? FYI: I am using JPA and Hibernate with Struts2 and Spring. The database being used is DB2 UDB8.2 Please help!

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• JPA + EJB + JSF: how can design complicated query

  - by Harry Pham

  I am using netbean 6.8 btw. Let say that I have 4 different tables: Company, Facility, Project, and Document. So the relationship is this. A company can have multiple facilities. A facility can have multiple projects, and a project can have multiple documents. Company: +companyNum: PK +facilityNum: FK Facility: +facilityNum: PK +projectNum: FK Project: +projectNum: PK +drawingNum: FK So when I create Entity Class From Database in netbean 6.8, I have 4 entity classes that named after the above 4 tables. So if I want to see all the Document in the database, then it is easy. In my SessionBean, I would do this: @PersistenceContext private EntityManager em; List<Document> documents = em.createNamedQuery("Document.findAll").getResultList(); However, that is not all what I need. Let say that I want to know all the Document from a particular Company, or all the Document from a particular Project from a particular Facility from a particular Company. I am very new to JPA + EJB + JSF as a whole. Please help me out.

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• JPA @OneToMany and composite PK

  - by Fleuri F

  Good Morning, I am working on project using JPA. I need to use a @OneToMany mapping on a class that has three primary keys. You can find the errors and the classes after this. If anyone has an idea! Thanks in advance! FF javax.persistence.PersistenceException: No Persistence provider for EntityManager named JTA_pacePersistence: Provider named oracle.toplink.essentials.PersistenceProvider threw unexpected exception at create EntityManagerFactory: javax.persistence.PersistenceException javax.persistence.PersistenceException: Exception [TOPLINK-28018] (Oracle TopLink Essentials - 2.0.1 (Build b09d-fcs (12/06/2007))): oracle.toplink.essentials.exceptions.EntityManagerSetupException Exception Description: predeploy for PersistenceUnit [JTA_pacePersistence] failed. Internal Exception: Exception [TOPLINK-7220] (Oracle TopLink Essentials - 2.0.1 (Build b09d-fcs (12/06/2007))): oracle.toplink.essentials.exceptions.ValidationException Exception Description: The @JoinColumns on the annotated element [private java.util.Set isd.pacepersistence.common.Action.permissions] from the entity class [class isd.pacepersistence.common.Action] is incomplete. When the source entity class uses a composite primary key, a @JoinColumn must be specified for each join column using the @JoinColumns. Both the name and the referenceColumnName elements must be specified in each such @JoinColumn. at oracle.toplink.essentials.internal.ejb.cmp3.EntityManagerSetupImpl.predeploy(EntityManagerSetupImpl.java:643) at oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider.createEntityManagerFactory(EntityManagerFactoryProvider.java:196) at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:110) at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:83) at isd.pacepersistence.common.DataMapper.(Unknown Source) at isd.pacepersistence.server.MainServlet.getDebugCase(Unknown Source) at isd.pacepersistence.server.MainServlet.doGet(Unknown Source) at javax.servlet.http.HttpServlet.service(HttpServlet.java:718) at javax.servlet.http.HttpServlet.service(HttpServlet.java:831) at org.apache.catalina.core.ApplicationFilterChain.servletService(ApplicationFilterChain.java:411) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:290) at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:271) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:202) There is the source code of my classes : Action : @Entity @Table(name="action") public class Action { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private int num; @ManyToOne(cascade= { CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH }) @JoinColumn(name="domain_num") private Domain domain; private String name; private String description; @OneToMany @JoinTable(name="permission", joinColumns= { @JoinColumn(name="action_num", referencedColumnName="action_num", nullable=false, updatable=false) }, inverseJoinColumns= { @JoinColumn(name="num") }) private Set<Permission> permissions; public Action() { } Permission : @SuppressWarnings("serial") @Entity @Table(name="permission") public class Permission implements Serializable { @EmbeddedId private PermissionPK primaryKey; @ManyToOne @JoinColumn(name="action_num", insertable=false, updatable=false) private Action action; @ManyToOne @JoinColumn(name="entity_num", insertable=false, updatable=false) private isd.pacepersistence.common.Entity entity; @ManyToOne @JoinColumn(name="class_num", insertable=false, updatable=false) private Clazz clazz; private String kondition; public Permission() { } PermissionPK : @SuppressWarnings("serial") @Entity @Table(name="permission") public class Permission implements Serializable { @EmbeddedId private PermissionPK primaryKey; @ManyToOne @JoinColumn(name="action_num", insertable=false, updatable=false) private Action action; @ManyToOne @JoinColumn(name="entity_num", insertable=false, updatable=false) private isd.pacepersistence.common.Entity entity; @ManyToOne @JoinColumn(name="class_num", insertable=false, updatable=false) private Clazz clazz; private String kondition; public Permission() { }

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• JPA @ManyToOne and composite PK

  - by Fleuri F

  Good Morning, I am working on project using JPA. I need to use a @ManyToOne mapping on a class that has three primary keys. You can find the errors and the classes after this. If anyone has an idea! Thanks in advance! FF javax.persistence.PersistenceException: No Persistence provider for EntityManager named JTA_pacePersistence: Provider named oracle.toplink.essentials.PersistenceProvider threw unexpected exception at create EntityManagerFactory: javax.persistence.PersistenceException javax.persistence.PersistenceException: Exception [TOPLINK-28018] (Oracle TopLink Essentials - 2.0.1 (Build b09d-fcs (12/06/2007))): oracle.toplink.essentials.exceptions.EntityManagerSetupException Exception Description: predeploy for PersistenceUnit [JTA_pacePersistence] failed. Internal Exception: Exception [TOPLINK-7220] (Oracle TopLink Essentials - 2.0.1 (Build b09d-fcs (12/06/2007))): oracle.toplink.essentials.exceptions.ValidationException Exception Description: The @JoinColumns on the annotated element [private java.util.Set isd.pacepersistence.common.Action.permissions] from the entity class [class isd.pacepersistence.common.Action] is incomplete. When the source entity class uses a composite primary key, a @JoinColumn must be specified for each join column using the @JoinColumns. Both the name and the referenceColumnName elements must be specified in each such @JoinColumn. at oracle.toplink.essentials.internal.ejb.cmp3.EntityManagerSetupImpl.predeploy(EntityManagerSetupImpl.java:643) at oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider.createEntityManagerFactory(EntityManagerFactoryProvider.java:196) at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:110) at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:83) at isd.pacepersistence.common.DataMapper.(Unknown Source) at isd.pacepersistence.server.MainServlet.getDebugCase(Unknown Source) at isd.pacepersistence.server.MainServlet.doGet(Unknown Source) at javax.servlet.http.HttpServlet.service(HttpServlet.java:718) at javax.servlet.http.HttpServlet.service(HttpServlet.java:831) at org.apache.catalina.core.ApplicationFilterChain.servletService(ApplicationFilterChain.java:411) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:290) at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:271) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:202) There is the source code of my classes : Action : @Entity @Table(name="action") public class Action { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private int num; @ManyToOne(cascade= { CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH }) @JoinColumn(name="domain_num") private Domain domain; private String name; private String description; @OneToMany @JoinTable(name="permission", joinColumns= { @JoinColumn(name="action_num", referencedColumnName="action_num", nullable=false, updatable=false) }, inverseJoinColumns= { @JoinColumn(name="num") }) private Set<Permission> permissions; public Action() { } Permission : @SuppressWarnings("serial") @Entity @Table(name="permission") public class Permission implements Serializable { @EmbeddedId private PermissionPK primaryKey; @ManyToOne @JoinColumn(name="action_num", insertable=false, updatable=false) private Action action; @ManyToOne @JoinColumn(name="entity_num", insertable=false, updatable=false) private isd.pacepersistence.common.Entity entity; @ManyToOne @JoinColumn(name="class_num", insertable=false, updatable=false) private Clazz clazz; private String kondition; public Permission() { } PermissionPK : @SuppressWarnings("serial") @Entity @Table(name="permission") public class Permission implements Serializable { @EmbeddedId private PermissionPK primaryKey; @ManyToOne @JoinColumn(name="action_num", insertable=false, updatable=false) private Action action; @ManyToOne @JoinColumn(name="entity_num", insertable=false, updatable=false) private isd.pacepersistence.common.Entity entity; @ManyToOne @JoinColumn(name="class_num", insertable=false, updatable=false) private Clazz clazz; private String kondition; public Permission() { }

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• JPA One To Many Relationship Persistence Bug

  - by Brian

  Hey folks, I've got a really weird problem with a bi-directional relationship in jpa (hibernate implementation). A User is based in one Region, and a Region can contain many Users. So...relationship is as follows: Region object: @OneToMany(mappedBy = "region", fetch = FetchType.LAZY, cascade = CascadeType.ALL) public Set<User> getUsers() { return users; } public void setUsers(Set<User> users) { this.users = users; } User object: @ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.EAGER) @JoinColumn(name = "region_fk") public Region getRegion() { return region; } public void setRegion(Region region) { this.region = region; } So, the relationship as you can see above is Lazy on the region side, ie, I don't want the region to eager load all the users. Therefore, I have the following code within my DAO layer to add a user to an existing user to an existing region object... public User setRegionForUser(String username, Long regionId){ Region r = (Region) this.get(Region.class, regionId); User u = (User) this.get(User.class, username); u.setRegion(r); Set<User> users = r.getUsers(); users.add(u); System.out.println("The number of users in the set is: "+users.size()); r.setUsers(users); this.update(r); return (User)this.update(u); } The problem is, when I run a little unit test to add 5 users to my region object, I see that the region.getUsers() set always stays stuck at 1 object...somehow the set isn't getting added to. My unit test code is as follows: public void setUp(){ System.out.println("calling setup method"); Region r = (Region)ManagerFactory.getCountryAndRegionManager().get(Region.class, Long.valueOf("2")); for(int i = 0; i<loop; i++){ User u = new User(); u.setUsername("username_"+i); ManagerFactory.getUserManager().update(u); ManagerFactory.getUserManager().setRegionForUser("username_"+i, Long.valueOf("2")); } } public void tearDown(){ System.out.println("calling teardown method"); for(int i = 0; i<loop; i++){ ManagerFactory.getUserManager().deleteUser("username_"+i); } } public void testGetUsersForRegion(){ Set<User> totalUsers = ManagerFactory.getCountryAndRegionManager().getUsersInRegion(Long.valueOf("2")); System.out.println("Expecting 5, got: "+totalUsers.size()); this.assertEquals(5, totalUsers.size()); } So the test keeps failing saying there is only 1 user instead of the expected 5. Any ideas what I'm doing wrong? thanks very much, Brian

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• How to know if a detached JPA entity has already been persisted or not ?

  - by snowflake

  I have a JPA entity instance in the web UI layer of my application. I'd like to know at anytime if this entity has been already persisted in database or if it is only present in the user session. It would be in the business layer, I would use entitymanager.contains(Entity) method, but in my UI layer I think I need an extra attribute indicating whether the entity has been saved or not. How implement that ? I'm considering following option for the moment: - a JPA attribute with a default value set by the database, but would force a new read after each update ? - a non JPA attribute manually set in my code or automatically set by JPA? Any advice / other suggestions ? I'm using JPA 1 with Hibernate 3.2 implementation and would prefer stick to the standard.

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• Eager/Lazy loaded member always empty with JPA one-to-many relationship

  - by Kaleb Pederson

  I have two entities, a User and Role with a one-to-many relationship from user to role. Here's what the tables look like: mysql> select * from User; +----+-------+----------+ | id | name | password | +----+-------+----------+ | 1 | admin | admin | +----+-------+----------+ 1 row in set (0.00 sec) mysql> select * from Role; +----+----------------------+---------------+----------------+ | id | description | name | summary | +----+----------------------+---------------+----------------+ | 1 | administrator's role | administrator | Administration | | 2 | editor's role | editor | Editing | +----+----------------------+---------------+----------------+ 2 rows in set (0.00 sec) And here's the join table that was created: mysql> select * from User_Role; +---------+----------+ | User_id | roles_id | +---------+----------+ | 1 | 1 | | 1 | 2 | +---------+----------+ 2 rows in set (0.00 sec) And here's the subset of orm.xml that defines the tables and relationships: <entity class="User" name="User"> <table name="User" /> <attributes> <id name="id"> <generated-value strategy="AUTO" /> </id> <basic name="name"> <column name="name" length="100" unique="true" nullable="false"/> </basic> <basic name="password"> <column length="255" nullable="false" /> </basic> <one-to-many name="roles" fetch="EAGER" target-entity="Role" /> </attributes> </entity> <entity class="Role" name="Role"> <table name="Role" /> <attributes> <id name="id"> <generated-value strategy="AUTO"/> </id> <basic name="name"> <column name="name" length="40" unique="true" nullable="false"/> </basic> <basic name="summary"> <column name="summary" length="100" nullable="false"/> </basic> <basic name="description"> <column name="description" length="255"/> </basic> </attributes> </entity> Yet, despite that, when I retrieve the admin user, I get back an empty collection. I'm using Hibernate as my JPA provider and it shows the following debug SQL: select user0_.id as id8_, user0_.name as name8_, user0_.password as password8_ from User user0_ where user0_.name=? limit ? When the one-to-many mapping is lazy loaded, that's the only query that's made. This correctly retrieves the one admin user. I changed the relationship to use eager loading and then the following query is made in addition to the above: select roles0_.User_id as User1_1_, roles0_.roles_id as roles2_1_, role1_.id as id9_0_, role1_.description as descript2_9_0_, role1_.name as name9_0_, role1_.summary as summary9_0_ from User_Role roles0_ left outer join Role role1_ on roles0_.roles_id=role1_.id where roles0_.User_id=? Which results in the following results: +----------+-----------+--------+----------------------+---------------+----------------+ | User1_1_ | roles2_1_ | id9_0_ | descript2_9_0_ | name9_0_ | summary9_0_ | +----------+-----------+--------+----------------------+---------------+----------------+ | 1 | 1 | 1 | administrator's role | administrator | Administration | | 1 | 2 | 2 | editor's role | editor | Editing | +----------+-----------+--------+----------------------+---------------+----------------+ 2 rows in set (0.00 sec) Hibernate obviously knows about the roles, yet getRoles() still returns an empty collection. Hibernate also recognized the relationship sufficiently to put the data in the first place. What problems can cause these symptoms?

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• "Oracle Certified Expert, Java Platform, Enterprise Edition 6 Java Persistence API Developer" Preparation

  - by Matt

  I have been working with Hibernate for a fews years now, and I want to solidify and demonstrate my knowledge by taking the Oracle JPA certification, also known as: "Oracle Certified Expert, Java Platform, Enterprise Edition 6 Java Persistence API Developer (CX-310-094)" There is a training course provided by Oracle: "Building Database Driven Applications with JPA (SL-370-EE6)" But this costs $1800 and I think it would be overkill for my needs. Ideally, I would like a self study guide that will cover everything in the exam. I have looked for books and these seem like possibilities: Pro JPA 2: Mastering the Java Persistence API (Expert's Voice in Java Technology) and Beginning Java EE 6 with GlassFish 3 2nd Edition (Expert's Voice in Java Technology) But these aren't checklist type study guides as far as I am aware. I found the official SCJP study guide very useful, but I think the equivalent text for the JPA exam isn't out yet. If anyone has taken this exam, I would be grateful to hear how you prepared for it. Thanks!

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• "Oracle Certified Expert, Java Platform, Enterprise Edition 6 Java Persistence API Developer" Preparation

  - by Matt

  I have been working with Hibernate for a fews years now, and I want to solidify and demonstrate my knowledge by taking the Oracle JPA certification, also known as: "Oracle Certified Expert, Java Platform, Enterprise Edition 6 Java Persistence API Developer (CX-310-094)" There is a training course provided by Oracle: "Building Database Driven Applications with JPA (SL-370-EE6)" But this costs $1800 and I think it would be overkill for my needs. Ideally, I would like a self study guide that will cover everything in the exam. I have looked for books and these seem like possibilities: Pro JPA 2: Mastering the Java Persistence API (Expert's Voice in Java Technology) and Beginning Java EE 6 with GlassFish 3 2nd Edition (Expert's Voice in Java Technology) But these aren't checklist type study guides as far as I am aware. I found the official SCJP study guide very useful, but I think the equivalent text for the JPA exam isn't out yet. If anyone has taken this exam, I would be grateful to hear how you prepared for it. Thanks!

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• JPA behaviour...

  - by Marcel

  Hi I have some trouble understanding a JPA behaviour. Mabye someone could give me a hint. Situation: Product entity: @Entity public class Product implements Serializable { ... @OneToMany(mappedBy="product", fetch=FetchType.EAGER) private List<ProductResource> productResources = new ArrayList<ProductResource>(); .... public List<ProductResource> getProductResources() { return productResources; } public boolean equals(Object obj) { if (obj == this) return true; if (obj == null) return false; if (!(obj instanceof Product)) return false; Product p = (Product) obj; return p.productId == productId; } } Resource entity: @Entity public class Resource implements Serializable { ... @OneToMany(mappedBy="resource", fetch=FetchType.EAGER) private List<ProductResource> productResources = new ArrayList<ProductResource>(); ... public void setProductResource(List<ProductResource> productResource) { this.productResources = productResource; } public List<ProductResource> getProductResources() { return productResources; } public boolean equals(Object obj) { if (obj == this) return true; if (obj == null) return false; if (!(obj instanceof Resource)) return false; Resource r = (Resource) obj; return (long)resourceId==(long)r.resourceId; } } ProductResource Entity: This is a JoinTable (association class) with additional properties (amount). It maps Product and Resources. @Entity public class ProductResource implements Serializable { ... @JoinColumn(nullable=false, updatable=false) @ManyToOne(fetch=FetchType.EAGER, cascade=CascadeType.PERSIST) private Product product; @JoinColumn(nullable=false, updatable=false) @ManyToOne(fetch=FetchType.EAGER, cascade=CascadeType.PERSIST) private Resource resource; private int amount; public void setProduct(Product product) { this.product = product; if(!product.getProductResources().contains((this))){ product.getProductResources().add(this); } } public Product getProduct() { return product; } public void setResource(Resource resource) { this.resource = resource; if(!resource.getProductResources().contains((this))){ resource.getProductResources().add(this); } } public Resource getResource() { return resource; } ... public boolean equals(Object obj) { if (obj == this) return true; if (obj == null) return false; if (!(obj instanceof ProductResource)) return false; ProductResource pr = (ProductResource) obj; return (long)pr.productResourceId == (long)productResourceId; } } This is the Session Bean (running on glassfish). @Stateless(mappedName="PersistenceManager") public class PersistenceManagerBean implements PersistenceManager { @PersistenceContext(unitName = "local_mysql") private EntityManager em; public Object create(Object entity) { em.persist(entity); return entity; } public void delete(Object entity) { em.remove(em.merge(entity)); } public Object retrieve(Class entityClass, Long id) { Object entity = em.find(entityClass, id); return entity; } public void update(Object entity) { em.merge(entity); } } I call the session Bean from a java client: public class Start { public static void main(String[] args) throws NamingException { PersistenceManager pm = (PersistenceManager) new InitialContext().lookup("java:global/BackITServer/PersistenceManagerBean"); ProductResource pr = new ProductResource(); Product p = new Product(); Resource r = new Resource(); pr.setProduct(p); pr.setResource(r); ProductResource pr_stored = (ProductResource) pm.create(pr); pm.delete(pr_stored); Product p_ret = (Product) pm.retrieve(Product.class, pr_stored.getProduct().getProductId()); // prints out true ???????????????????????????????????? System.out.println(p_ret.getProductResources().contains(pr_stored)); } } So here comes my problem. Why is the ProductResource entity still in the List productResources(see code above). The productResource tuple in the db is gone after the deletion and I do newly retrieve the Product entity. If I understood right every method call of the client happens in a new persistence context, but here i obviously get back the non-refreshed product object!? Any help is appreciated Thanks Marcel

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• JPA2 adding referential contraint to table complicates criteria query with lazy fetch, need advice

  - by Quaternion

  Following is a lot of writing for what I feel is a pretty simple issue. Root of issue is my ignorance, not looking so much for code but advice. Table: Ininvhst (Inventory-schema inventory history) column ihtran (inventory history transfer code) using an old entity mapping I have: @Basic(optional = false) @Column(name = "IHTRAN") private String ihtran; ihtran is really a foreign key to table Intrnmst ("Inventory Transfer Master" which contains a list of "transfer codes"). This was not expressed in the database so placed a referential constraint on Ininvhst re-generating JPA2 entity classes produced: @JoinColumn(name = "IHTRAN", referencedColumnName = "TMCODE", nullable = false) @ManyToOne(optional = false) private Intrnmst intrnmst; Now previously I was using JPA2 to select the records/(Ininvhst entities) from the Ininvhst table where "ihtran" was one of a set of values. I used in.value() to do this... here is a snippet: cq = cb.createQuery(Ininvhst.class); ... In in = cb.in(transactionType); //Get in expression for transacton types for (String s : transactionTypes) { //has a value in = in.value(s);//check if the strings we are looking for exist in the transfer master } predicateList.add(in); My issue is that the Ininvhst used to contain a string called ihtran but now it contains Ininvhst... So I now need a path expression: this.predicateList = new ArrayList<Predicate>(); if (transactionTypes != null && transactionTypes.size() > 0) { //list of strings has some values Path<Intrnmst> intrnmst = root.get(Ininvhst_.intrnmst); //get transfermaster from Ininvhst Path<String> transactionType = intrnmst.get(Intrnmst_.tmcode); //get transaction types from transfer master In<String> in = cb.in(transactionType); //Get in expression for transacton types for (String s : transactionTypes) { //has a value in = in.value(s);//check if the strings we are looking for exist in the transfer master } predicateList.add(in); } Can I add ihtran back into the entity along with a join column that is both references "IHTRAN"? Or should I use a projection to somehow return Ininvhst along with the ihtran string which is now part of the Intrnmst entity. Or should I use a projection to return Ininvhst and somehow limit Intrnmst just just the ihtran string. Further information: I am using the resulting list of selected Ininvhst objects in a web application, the class which contains the list of Ininvhst objects is transformed into a json object. There are probably quite a few serialization methods that would navigate the object graph the problem is that my current fetch strategy is lazy so it hits the join entity (Intrnmst intrnmst) and there is no Entity Manager available at that point. At this point I have prevented the object from serializing the join column but now I am missing a critical piece of data. I think I've said too much but not knowing enough I don't know what you JPA experts need. What I would like is my original object to have both a string object and be able to join on the same column (ihtran) and have it as a string too, but if this isn't possible or advisable I want to hear what I should do and why. Pseudo code/English is more than fine.

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• Issue in configuring JPA with Spring 3 in Jboss 4.2.2 server.

  - by KVMKReddy

  Hi, I am facing issues in configuring JPA with Spring 3 in JBoss 4.2.2 server. Please find the below file of persistence.xml. <?xml version="1.0" encoding="UTF-8"?> <persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0"> <persistence-unit name="TestPU"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <jta-data-source>java:/TestDS</jta-data-source> <properties> <property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect"/> <property name="hibernate.show_sql" value="true"/> </properties> </persistence-unit> </persistence> My spring-beans.xml is as below <bean id="MyAdvise" class=".......Aspect"> <property name="persister"> <bean id="dbPersister" class="..............DataBasePersister"> </bean> </property> </bean> <bean id="localContainerEntityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> <property name="jpaVendorAdapter"> <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"> <property name="showSql" value="true"/> <property name="database" value="ORACLE"/> </bean> </property> <property name="jpaProperties"> <props> <prop key="hibernate.transaction.manager_lookup_class">org.hibernate.transaction.JBossTransactionManagerLookup</prop> </props> </property> </bean> <bean id="myTxManager" class="org.springframework.orm.jpa.JpaTransactionManager"> <property name="entityManagerFactory" ref="localContainerEntityManagerFactory"/> </bean> <tx:annotation-driven transaction-manager="myTxManager" /> My persister bean is as follows. public class DataBasePersister implements IPersister { private static Logger log = Logger.getLogger(DataBasePersister.class); // The Entity Manager @PersistenceContext protected EntityManager entityManager; @Transactional(readOnly = false) public void persist(Object data) { log.info("IN persist() call. Is the data can castable to MethodStats -->:"+(data instanceof MethodStats)); log.info("Entity Manager instance -->:"+(entityManager)); ---------------------- ---------------------- ---------------------- } } I am getting the following exception when the spring container creating my persister bean org.springframework.transaction.CannotCreateTransactionException: Could not open JPA EntityManager for transaction; nested exception is java.lang.IllegalStateException: JTA EntityManager cannot access a transactions at org.springframework.orm.jpa.JpaTransactionManager.doBegin(JpaTransactionManager.java:382) at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:371) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:585) at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309) at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:166) at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:89) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172) at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202) at $Proxy147.getTransaction(Unknown Source) at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:335) at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:105) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172) at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:89) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172) at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202) at $Proxy141.persist(Unknown Source) at com.adp.sbs.aop.aspectj.SBSMethodStatsCollectorAspect.doAround(SBSMethodStatsCollectorAspect.java:63) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:585) at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621) at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610) at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:161) at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:89) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172) at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:621) at com.adp.sbs.aop.test.TestMethodLevelAnnotationStats$$EnhancerByCGLIB$$efbc78a8.MethodWithOneParamsAndReturnTypeAsString(<generated>) at com.adp.sbs.aop.test.SimpleTestServlet.testMethodAnnotations(SimpleTestServlet.java:46) at com.adp.sbs.aop.test.SimpleTestServlet.doPost(SimpleTestServlet.java:40) at com.adp.sbs.aop.test.SimpleTestServlet.doGet(SimpleTestServlet.java:33) at javax.servlet.http.HttpServlet.service(HttpServlet.java:690) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175) at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:179) at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446) at java.lang.Thread.run(Thread.java:595) Caused by: java.lang.IllegalStateException: JTA EntityManager cannot access a transactions at org.hibernate.ejb.AbstractEntityManagerImpl.getTransaction(AbstractEntityManagerImpl.java:316) at org.springframework.orm.jpa.DefaultJpaDialect.beginTransaction(DefaultJpaDialect.java:70) at org.springframework.orm.jpa.vendor.HibernateJpaDialect.beginTransaction(HibernateJpaDialect.java:57) at org.springframework.orm.jpa.JpaTransactionManager.doBegin(JpaTransactionManager.java:332) Can you somebody please suggest me how to resolve this.

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• Eclipselink problem in a javase project

  - by arinte

  I am getting this error when I am running my eclipselink project. [EL Warning]: 2008.12.05 11:47:08.056--java.lang.NoClassDefFoundError: org/jboss/resource/adapter/jdbc/ValidConnectionChecker was thrown on attempt of PersistenceLoadProcessor to load class com.mysql.jdbc.integration.jboss.MysqlValidConnectionChecker. The class is ignored. Exception in thread "main" java.lang.NoClassDefFoundError: org/jboss/resource/adapter/jdbc/ValidConnectionChecker at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(Unknown Source) at java.security.SecureClassLoader.defineClass(Unknown Source) at java.net.URLClassLoader.defineClass(Unknown Source) at java.net.URLClassLoader.access$000(Unknown Source) at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at org.eclipse.persistence.internal.jpa.deployment.PersistenceUnitProcessor.loadClass(PersistenceUnitProcessor.java:261) at org.eclipse.persistence.internal.jpa.metadata.MetadataProcessor.initPersistenceUnitClasses(MetadataProcessor.java:247) at org.eclipse.persistence.internal.jpa.metadata.MetadataProcessor.processEntityMappings(MetadataProcessor.java:422) at org.eclipse.persistence.internal.jpa.deployment.PersistenceUnitProcessor.processORMetadata(PersistenceUnitProcessor.java:299) at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.predeploy(EntityManagerSetupImpl.java:830) at org.eclipse.persistence.internal.jpa.deployment.JPAInitializer.callPredeploy(JPAInitializer.java:101) at org.eclipse.persistence.internal.jpa.deployment.JPAInitializer.initPersistenceUnits(JPAInitializer.java:149) at org.eclipse.persistence.internal.jpa.deployment.JPAInitializer.initialize(JPAInitializer.java:135) at org.eclipse.persistence.jpa.PersistenceProvider.createEntityManagerFactory(PersistenceProvider.java:104) at org.eclipse.persistence.jpa.PersistenceProvider.createEntityManagerFactory(PersistenceProvider.java:64) at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:83) at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:60) at Main.main(Main.java:32) Caused by: java.lang.ClassNotFoundException: org.jboss.resource.adapter.jdbc.ValidConnectionChecker at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClassInternal(Unknown Source) ... 24 more Any ideas? Why would eclipselink need something from jboss? What jboss jar do I need. I would use open jpa, but for some reason after quit a few persists from my app it starts giving a bunch of stackoverflow errors.

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• [hibernate - jpa ] good practices and bad practices

  - by blow

  Hi all, i have some questions about interaction with hibernate. openSession or getCurrentSession (without jta, thread insted)? How mix session operations with swing gui? Is good have something like this in a javabean class? public void actionPerformed(ActionEvent event) { // session code } Can i add methods to my entities that contains hql queries or is a bad practice? For example: // This method is in an entity MyOtherEntity.java class public int getDuration(){ Session session=HibernateUtil.getSessionFactory().getCurrentSession(); session.beginTransaction(); int sum=(Integer)session.createQuery("select sum(e.duration) as duration from MyEntity as e where e.myOtherEntity.id=:id group by e.name"). .setLong("id", getId()); .uniqueResult(); return sum; } In alternative how can i do this in a better and elegant way? Thanks.

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• Calling next value of a sequence in jpa

  - by Javi

  Hello, I have a class mapped as an Entity to persist it in a database. I have an id field as the primary key so every time the object is persisted the value of the id is retrieved from the sequence "myClass_pk_seq", a code like the following one. @Entity @Table(name="myObjects") public class MyClass { @Id @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="sequence") @SequenceGenerator(name="sequence", sequenceName="myClass_pk_seq", allocationSize=1) @Column(name="myClassId") private Integer id; ... } I need to get the next value of the sequence myClass_pk_seq to reserve that value (get the next value of the sequence and the current value is incremented), but without saving the object. How can I call the next value of a sequence when it's defined like this? Thanks.

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• Hibernate ResultTransformer with JPA API

  - by Timo Westkämper

  Has anyone figured out a smart way to do query result transformation through a similar mechanism like specifying a ResultTransformer in Hibernate? All I can think of is transforming each result row after it has been returned by the Query. Is there any other way? For constructor projections (e.g. new DTO(arg1, arg2)) it can be defined in the JPQL query, at least for Hibernate, but how about other cases?

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• JPA Lookup Hierarchy Mapping

  - by Andy Trujillo

  Given a lookup table: | ID | TYPE | CODE | DESCRIPTION | | 1 | ORDER_STATUS | PENDING | PENDING DISPOSITION | | 2 | ORDER_STATUS | OPEN | AWAITING DISPOSITION | | 3 | OTHER_STATUS | OPEN | USED BY OTHER ENTITY | If I have an entity: @MappedSuperclass @Table(name="LOOKUP") @Inheritance(strategy=InheritanceType.SINGLE_TABLE) @DiscriminatorColumn(name="TYPE", discriminatorType=DiscriminatorType.STRING) public abstract class Lookup { @Id @Column(name="ID") int id; @Column(name="TYPE") String type; @Column(name="CODE") String code; @Column(name="DESC") String description; ... } Then a subclass: @Entity @DiscriminatorValue("ORDER_STATUS") public class OrderStatus extends Lookup { } The expectation is to map it: @Entity @Table(name="ORDERS") public class OrderVO { ... @ManyToOne @JoinColumn(name="STATUS", referencedColumnName="CODE") OrderStatus status; ... } So that the CODE is stored in the database. I expected that if I wrote: OrderVO o = entityManager.find(OrderVO.class, 123); the SQL generated using OpenJPA would look something like: SELECT t0.id, ..., t1.CODE, t1.TYPE, t1.DESC FROM ORDERS t0 LEFT OUTER JOIN LOOKUP t1 ON t0.STATUS = t1.CODE AND t1.TYPE = 'ORDER_STATUS' WHERE t0.ID = ? But the actual SQL that gets generated is missing the AND t1.TYPE = 'ORDER_STATUS' This causes a problem when the CODE is not unique. Is there a way to have the discriminator included on joins or am I doing something wrong here?

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• Interface between two related JPA entities

  - by OpenSource

  The scenario is as below (tables shown) Delivery table ------ id channelId type 10 100 fax 20 200 email Fax table ---- id number 100 1234567 101 1234598 Email table ----- id email 200 [email protected] 201 [email protected] basically a one to one relationship between the delivery and the channel entity but since each concrete channel(fax, email) has different members I want to create a generic interface (channel) between the two entities and use it for the @OneToOne relationship. Seems to me a simple scenario where lot of you might have already gone through but I'm unable to succeed. I tried putting that targetEntity thing but no use. Still says "delivery references an unknown entity" Any ideas? thanks in advance

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• JPA ManyToMany problem...

  - by Parhs

  Hello i have an Entity Exam @Id @GeneratedValue(strategy=GenerationType.TABLE) private Long id; ..... ...... @ManyToMany private List<Exam> exams; @ManyToMany(mappedBy="id") private List<Exam> parentExams; The problem is that @ManyToMany private List<Exam> exams; is ok works great... but this doesnt validate?! @ManyToMany(mappedBy="id") private List<Exam> parentExams; Any idea what to do ? I just want to get the exams that are parents of the current exam. ??e???? ??µ?sµat??? ?aµe??

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