Using lazy for properties in Hibernate

Question

The lazy attribute for property tag in hibernate allows to lazily load the property as per the link: http://docs.jboss.org/hibernate/orm/3.3/reference/en-US/html/mapping.htm

Answer 1

With Hibernate 5, this can be done easily using bytecode enhancement.

First, you need to add the following Maven plugin:

    org.hibernate.orm.tooling
    hibernate-enhance-maven-plugin
    ${hibernate.version}
    
        
            
                true
            
            
                enhance
            
        
    

Then, you can simply annotate your entity properties with @Basic(fetch = FetchType.LAZY):

@Entity(name = "Event")
@Table(name = "event")
public class Event extends BaseEntity {

    @Type(type = "jsonb")
    @Column(columnDefinition = "jsonb")
    @Basic(fetch = FetchType.LAZY)
    private Location location;

    public Location getLocation() {
        return location;
    }

    public void setLocation(Location location) {
        this.location = location;
    }
}

When you fetch the entity:

Event event = entityManager.find(Event.class, 
    eventHolder.get().getId());

LOGGER.debug("Fetched event");
assertEquals("Cluj-Napoca", event.getLocation().getCity());

Hibernate is going to load the lazy property using a secondary select:

SELECT e.id AS id1_0_0_
FROM   event e
WHERE  e.id = 1

-- Fetched event

SELECT e.location AS location2_0_
FROM   event e
WHERE  e.id = 1