jpa-2.0

问题 I just want to know what is the difference between all these annotations. Why are we using these... means they have no effect especially field level and property level. And what is the purpose of using mixed level annotation like: @Entity @Access(AccessType.FIELD) class Employee { // why their is a field level access private int id; // whats the purpose of transient here @Transient private String phnnumber; // why its a property level access @Access(AccessType.property) public String

问题 Is it possible to select, say, only properties A and B from an object using a JPA query without using criteria queries? To select all properties I'd just do something like: SELECT i FROM ObjectName i WHERE i.id = 10 But I have an object with many properties on a legacy system, and want to select just a few even though I'm aware selecting several properties is usually quick. Is this possible without using criteria queries? Thank you! 回答1: Yes, like in plain sql you could specify what kind of

问题 This is a followup question to: Is @ManyToMany(mappedBy = ... ) + @OrderColumn supported by the JPA? I'm referring to the @OrderColumn Java docs: http://docs.oracle.com/javaee/6/api/javax/persistence/OrderColumn.html The text there is the same as what the JPA 2 spec writes in section 11.1.39 OrderColumn Annotation . What does the part "the order column is not visible as part of the state of the entity" mean exactly ? There's a lot of room for interpretation on that. Does that mean the order

问题 In a legacy database, I have three tables: Users, Workgroups, and UsersWorkgroup. UsersWorkgroup stores what role a user has in a workgroup. Here are the relevant code snippets: @Entity @Table(name = "users_workgroup") public class UsersWorkgroup implements Serializable { private static final long serialVersionUID = 1L; @EmbeddedId protected UsersWorkgroupPK usersWorkgroupPK; @JoinColumn(name = "idworkgroup", referencedColumnName = "idworkgroup") @ManyToOne(optional = false) private Workgroup

问题 I had recently posted someone about populating a JTable, which is now fully functional. How ever, I am stuck over something else now, I'm hoping to achieve two specific thigns with this thread. One is to solve my problem, and the other is to have an answer ready for when others stumble across the same problem, cause I never found a proper answer to this yet. I have the following scenario Two tables: games id pk int genre int title varchar .... genre id pk int name varchar .. One game can only

问题 i am using sql, H2, and i am trying to make so that the ID of Usertable is auto_incremented. i tried all sql commands in H2 sql interface, didnot work out. alter table user alter column int not null auto_increment; this common one is even not working. is there any annotation of JPA for auto_incement may be? thanks a lot 回答1: You should use the JPA annotations @Id and @GeneratedValue for your ID. Your SQL looks valid. Can you post the error message? 回答2: I had the same problem. I am not sure

问题 How do you handle this situation where Oracle stores the empty string as a null in the database ? I would like it to be stored as an empty string as it is not as NULL, since issuing the query would be easier. Something like this would select the empty string and non-empty string, but not the null values select * from mytable where myfield like '%'; if i would like to select also the null values (which should be originally empty string), i would have to select like this : select * from mytable

问题 I'm having some trouble with setting the where clause of the following query: CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Configuration> cq = cb.createQuery(Configuration.class); Root<Configuration> conf = cq.from(Configuration.class); MapJoin<Configuration, String, Component> mapJoin = conf.join(Configuration_.components, JoinType.LEFT); cq.where(cb.and(cb.like(mapJoin.key(), "%abc%"), cb.like(mapJoin.value().get(Component_.displayName), "%def%"))); cq.select(pc); I am

问题 In my testing code I need to have a blank/empty database at each method. Is there code that would achieve that, to call in the @Before of the test? 回答1: Actually you always can use JPQL, em .createQuery("DELETE FROM MyEntity m") .executeUpdate() ; But note, there is no grants that entity cache would be cleaned also. But for unit-test purposes it is look like good solution. 回答2: In my testing code I need to have a blank/empty database at each method. I would run the test methods insider a

问题 Hy, i have a webapplication where i am trying to integrate JPA2(Hibernate)+Spring+Flyway I added flyway to my ApplicationContext like this: <bean id="flyway" class="org.flywaydb.core.Flyway" init-method="migrate"> <property name="baselineOnMigrate" value="true" /> <property name="dataSource" ref="dataSource" /> </bean> Theoretically this works fine and updates the schema with scripts that i save under db/migration. So far so good. The one problem that is left for me is that if i change