Custom query within JPA server-managed session - jdbc

Question

I'm trying to execute an unrelated query (other_table) within a JTA session (server-managed) in order to do some validations, before persisting the bean EJB into DB with JPA.
Here is what I want to do (aprox):
#PersistenceUnit(unitName="DynamicDatabase")
EntityManagerFactory emf;
#TransactionAttribute(TransactionAttributeType.REQUIRED)
private long nextEntryid() {
em = emf.createEntityManager();
Query query = em.createQuery("select t from OTHER_TABLE t");
// do some validation and checking
MyTable bean = new MyTable();
em.persist(bean);
}
However I keep getting a server error, it does not allow to interact with other database items that are not persisted:
org.apache.openjpa.persistence.ArgumentException:
An error occurred while parsing the query filter (query): The name "OTHER_TABLE" is not a recognized entity (...) Perhaps you meant MyTable, which is a close match.
<persistence-unit name="DynamicDatabase" transaction-type="JTA">
<jta-data-source>jdbc/DB2DynamicConnection</jta-data-source>
<class>jorge.java.dynamicdatabase.db.MyTable</class>
</properties>
</persistence-unit>
The question is: what is the proper way to query/alter another table within the same JPA DB connection and JTA transaction?
Pretty newby about this, please be patient with me. Been working on this very long.
Edit: I don't think it's related but FYI I'm using WebSphere Liberty Profile 8.5.5.4, JSDK 8u31, EclipseEE Luna 4.4.2 for Web Dev. Going to add it to tags.

Answer 1

The problem is that you have a #NamedQuery that references the entity OTHER_TABLE, and that does not exist or not marked as being an Entity (try in both Java class and persistence.xml).
If the OtherTable Java class is not an entity and if it MUST remain so, then you could use Constructors in JPQL-queries:
SELECT NEW com.domain.reports.MyReport(u.firstName, u.lastName, u.birthday) FROM User u
If you need to write plain SQL queries, then you could do it using native queries, as they are known in the JPA specification.

Answer 2

Based on Andrei's suggestion, the JPQL (Java Persistence Query Language) operates on objects, not on tables. This means that em.createQuery() can't be used for universal database interaction.
To execute any SQL statement generally speaking (inside the container-managed transaction JTA), it is necessary to get the DB connection from the entity manager (it will return the persistence context unit JPA).
// Get container's objects
em = emf.createEntityManager();
java.sql.Connection conn = em.unwrap(java.sql.Connection.class);
// Run the query
Statement sql = conn.createStatement();
ResultSet rs = sql.executeQuery("select * from OTHER_TABLE");
rs.next()
(...)
//Container-managed connection shouldn't be closed.
rs.close;
sql.close;
Notice that unwrap call works for JPA but not for Hibernate (other questions already exist on this point). Notice the different language used for the SQL statement select * from than a named query JPQL select t from. Exception handling must be also controlled as usual with a } finally { clause.
That way would allow to execute a complex custom statement within server-managed transaction without using JAVA entities and I can finally sleep.