Adding Criteria to SQL Queries in Hibernate: Methods Explained

How can we add criteria to a SQL query in Hibernate?

In Hibernate, you can add criteria to a SQL query using the Criteria API or the Query Language (HQL). Below are examples of how to use both methods to add criteria to your queries.

Using Criteria API

The Criteria API allows you to build queries programmatically. Here’s how you can use it:

1. Create a CriteriaBuilder: This is used to construct criteria queries, compound selections, expressions, predicates, etc.
2. Create a CriteriaQuery: This represents a query object.
3. Create a Root: This represents the entity you are querying.
4. Add Criteria: Use predicates to add conditions to your query.
5. Execute the Query: Use the EntityManager to execute the query.

Here’s an example:

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;
import java.util.List;

public class CriteriaExample {
    public static void main(String[] args) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("your-persistence-unit");
        EntityManager em = emf.createEntityManager();

        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<YourEntity> cq = cb.createQuery(YourEntity.class);
        Root<YourEntity> root = cq.from(YourEntity.class);

        // Adding criteria
        Predicate condition1 = cb.equal(root.get("fieldName"), "value");
        Predicate condition2 = cb.greaterThan(root.get("anotherField"), 10);
        cq.select(root).where(cb.and(condition1, condition2));

        List<YourEntity> results = em.createQuery(cq).getResultList();

        // Process results
        results.forEach(System.out::println);

        em.close();
        emf.close();
    }
}

Using HQL (Hibernate Query Language)

HQL is similar to SQL but operates on the entity objects rather than the database tables. You can add criteria using WHERE clauses.

Here’s an example:

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.query.Query;

import java.util.List;

public class HQLExample {
    public static void main(String[] args) {
        SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
        Session session = sessionFactory.openSession();
        Transaction transaction = session.beginTransaction();

        // HQL query with criteria
        String hql = "FROM YourEntity e WHERE e.fieldName = :value AND e.anotherField > :threshold";
        Query<YourEntity> query = session.createQuery(hql, YourEntity.class);
        query.setParameter("value", "someValue");
        query.setParameter("threshold", 10);

        List<YourEntity> results = query.getResultList();

        // Process results
        results.forEach(System.out::println);

        transaction.commit();
        session.close();
        sessionFactory.close();
    }
}

Summary

• Criteria API: Use it for a programmatic way to build queries with dynamic conditions.
• HQL: Use it for a more SQL-like syntax that operates on entity objects.

Both methods allow you to add criteria to your queries effectively, and you can choose based on your preference or specific use case.