If I’m using an ORM like JPA2 – where I have my entities that are mapped to my database, should I still be using a DAO? It seems like a lot more overhead. It is. And clearly, Java EE doesn’t encourage using the DAO pattern when using JPA (JPA already provides a standardized implementation of … Read more
Your approach is correct. Performance throughput? IMHO no need to worry – JPA 2.1 will use an equivalent mechanism. But make sure to write a realistic test to be on the safe side. What happens when there are multiple logged in users updating entities concurrently in their own scopes? All (non-dependend-scoped) bean references are proxied … Read more
I stumbled upon this issue as well. I would ultimately like to execute the following JPQL: SELECT COUNT(u) FROM ( SELECT DISTINCT u FROM User u JOIN u.roles r WHERE r.id IN (1) ) But this wasn’t possible, also not with criteria API. Research taught that this was just a design limitation in JPA. The … Read more
Either use Hibernate 5.2.0+ or for earlier Hibernate 5 add the following dependency: <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-java8</artifactId> <version>${hibernate.version}</version> </dependency>
In SQL the solution is very simple – join the table with a subquery, which gives you the most recent meeting for each attendee: select * from Meeting ALL join ( select max(meetingDate) as newest, attendee from Meeting group by attendee ) LATEST on ALL.meetingDate = LATEST.newest AND ALL.attendee = LATEST.attendee This works, and works … Read more
Is it possible to change the table name of an entity as follows on runtime since they have the same table structure after all? This is not really possible, at least not with standard JPA (which doesn’t mean I did it with non standard JPA) as mentioned in questions such as: In @Table(name = “tableName”) … Read more
You cannot catch ConstraintViolationException.class because it’s not propagated to that layer of your code, it’s caught by the lower layers, wrapped and rethrown under another type. So that the exception that hits your web layer is not a ConstraintViolationException. In my case, it’s a TransactionSystemException. I’m using @Transactional annotations from Spring with the JpaTransactionManager. The … Read more
You can do something like @NamedQuery(name=”findWhatever”, query=”SELECT new path.to.dto.MyDto(e.id, e.otherProperty) FROM Student e WHERE e.id = ?1″) Then the MyDto object would just need a constructor defined with the correct fields i.e. public MyDto(String id, String otherProperty) { this.id = id; this.otherProperty = otherProperty; }
You can pass an array of predicates to the CriteriaBuilder, deciding on equal or like as you go. For this, build a list and pack the contents of the list into an array in a single and statement. Like this: final List<Predicate> predicates = new ArrayList<Predicate>(); for (final Entry<String, String> e : myPredicateMap.entrySet()) { final … Read more
According to the JPA 2.0 specification, if you want to selectively cache entities using the @Cacheable annotation, you’re supposed to specify a <shared-cache-mode> in the persistence.xml (or the equivalent javax.persistence.sharedCache.mode when creating the EntityManagerFactory). Below, a sample persistence.xml with the relevant element and properties: <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_2_0.xsd” version=”2.0″> <persistence-unit name=”FooPu” transaction-type=”RESOURCE_LOCAL”> <provider>org.hibernate.ejb.HibernatePersistence</provider> … … Read more