Add support for query hints in JPA item readers

[maciejwalkowiak]

Expected Behavior

JpaCursorItemReaderBuilder should have an option to set fetchSize, similar to HibernateCursorItemReader (which is deprecated) and JdbcCursorItemReaderBuilder.

Current Behavior

There is no option to fetch size for query executed by JpaCursorItemReader. As a workaround I created FetchSizeAwareJpaQueryProvider. Pasting here in case someone would like to use it:

import jakarta.persistence.EntityManager;
import jakarta.persistence.Query;
import org.hibernate.jpa.AvailableHints;
import org.springframework.batch.item.database.orm.JpaQueryProvider;

/**
 * {@link JpaQueryProvider} implementation that enables setting "FETCH_SIZE" query hint on the JPA query.
 *
 * <a href="https://jdbc.postgresql.org/documentation/query/#getting-results-based-on-a-cursor">Getting results based on a cursor</a>
 * 
 * @author Maciej Walkowiak
 */
public class FetchSizeAwareJpaQueryProvider implements JpaQueryProvider {
    private final String queryString;
    private final int fetchSize;
    private EntityManager entityManager;

    public FetchSizeAwareJpaQueryProvider(String queryString, int fetchSize) {
        this.fetchSize = fetchSize;
        this.queryString = queryString;
    }

    @Override
    public Query createQuery() {
        Query query = this.entityManager.createQuery(queryString);
        query.setHint(AvailableHints.HINT_FETCH_SIZE, fetchSize);
        return query;
    }

    @Override
    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }
}

.. and use it like this:

new JpaCursorItemReaderBuilder<...>()
        .name("...")
        .entityManagerFactory(..)
        .queryProvider(new FetchSizeAwareJpaQueryProvider("<jpql query>", 100))
        .build();

If it makes sense I can see if I find time to contribute it.

[fmbenhassine]

Thank you for raising this, @maciejwalkowiak ! Support for query hints is indeed missing in JpaCursorItemReader and JpaPagingItemReader as well. Query hints should be set on the query just like query parameters. Respective builders should be updated as well.

I will plan this for v5.2 (the upcoming v5.1 is in feature freeze at this point). Contributions are welcome!

[baezzys]

Hi @fmbenhassine, I want to contribute to this issue. I'll create PR soon.