eclipselink – Make Me Engineer

Is it possible to write a generic enum converter for JPA?

June 13, 2023 by Tarik

Based on @scottb solution I made this, tested against hibernate 4.3: (no hibernate classes, should run on JPA just fine) Interface enum must implement: public interface PersistableEnum<T> { public T getValue(); } Base abstract converter: @Converter public abstract class AbstractEnumConverter<T extends Enum<T> & PersistableEnum<E>, E> implements AttributeConverter<T, E> { private final Class<T> clazz; public AbstractEnumConverter(Class<T> … Read more

JPA: JOIN in JPQL

June 13, 2023 by Tarik

Join on one-to-many relation in JPQL looks as follows: select b.fname, b.lname from Users b JOIN b.groups c where c.groupName = :groupName When several properties are specified in select clause, result is returned as Object[]: Object[] temp = (Object[]) em.createNamedQuery(“…”) .setParameter(“groupName”, groupName) .getSingleResult(); String fname = (String) temp[0]; String lname = (String) temp[1]; By the … Read more

No operator matches the given name and argument type(s). You might need to add explicit type casts. — Netbeans, Postgresql 8.4 and Glassfish

June 11, 2023 by Tarik

I had this issue, and solved. This was due to the WHERE clause contains String value instead of integer value.

Disable caching in JPA (eclipselink)

May 11, 2023 by Tarik

This behavior is correct, otherwise if you change object one and object two with different values you will have problems when persisting them. What is happening is the call to load object two updates the entity loaded in the first call. They must point to the same object since they ARE the same object. This … Read more

@XmlPath has no impact during the JAXB Marshalling

May 6, 2023 by Tarik

Finally was able to find the solution with a lot of assist from @andrewjames. Posting the solution for the same so somebody can find the solution quickly and do not end up spending whole day like me 🙂 You can also follow the steps mentioned by @andrewjames in his answer. Make sure you have only … Read more

Batch inserts using JPA EntityManager

April 28, 2023 by Tarik

Depending on whether the transaction encloses the loop, batching typically already happens in your case. JPA will collect all your updates in its L1 cache, and typically write that all to the DB in a batch when the transaction commits. This is not really that different with batching in JDBC, where every batch-item you add … Read more

Is it possible to output generated SQL using EclipseLink without having to increase log verbosity?

December 1, 2022 by Tarik

Put the following properties in your persistence.xml: <property name=”eclipselink.logging.level.sql” value=”FINE”/> <property name=”eclipselink.logging.parameters” value=”true”/> The latter is helpful, so that the values of the parameter are shown. An alternative is using log4jdbc or log4jdbc-remix.

What is referencedColumnName used for in JPA?

November 27, 2022 by Tarik

It is there to specify another column as the default id column of the other table, e.g. consider the following TableA id int identity tableb_key varchar TableB id int identity key varchar unique // in class for TableA @JoinColumn(name=”tableb_key”, referencedColumnName=”key”)

Java8 Collections.sort (sometimes) does not sort JPA returned lists

November 5, 2022 by Tarik

Well, this is a perfect didactic play telling you why programmers shouldn’t extend classes not designed for being subclassed. Books like “Effective Java” tell you why: the attempt to intercept every method to alter its behavior will fail when the superclass evolves. Here, IndirectList extends Vector and overrides almost all methods to modify its behavior, … Read more

Parameter in like clause JPQL

October 9, 2022 by Tarik

If you do LIKE :code and then do namedQuery.setParameter(“code”, “%” + this.value + “%”); Then value remains free from the ‘%’ sign. If you need to use it somewhere else in the same query simply use another parameter name other than ‘code’ .