Lazy fetching single column (class attribute) with Hibernate

Question

I have an old table that I\'m working with, which looks like this:

+------------------+--------------+------+-----+---------+-------+
| Field            | Ty         


        

Answer 1

I am aware of the date of this inquiry, however, I would have also attempted to use a projection value class that maps as subset of the columns, and use that projection with a specified named query which instantiates that projection value object, instead of the base object being referenced here.

I am working on a solution which uses this method so I do not currently have a full example. However, the basic idea is that you will create a JPA query which uses the "select NEW Projection_Object_Target" syntax, where the fields are directly referenced within the constructor of "Projection_Object_Target".

I.E. Use a constructor expression as follows:

SELECT NEW fully.qualified.package.name.ProjectionObject(baseObject.column_target_0,baseObject.column_target_1,...,baseObject.column_target_n) FROM BaseObjectMappedInDBTable AS baseObject

Generic example use-case:

String queryStr =
  "SELECT NEW fully.qualified.package.name.ProjectionObject(baseObject.column_target_0) " +
  "FROM BaseObjectMappedInTable AS baseObject";
TypedQuery<ProjectionObject> query =
  em.createQuery(queryStr, ProjectionObject.class);
List<ProjectionObject> results = query.getResultList();

Answer 2

For maven project it's needed to add following plugin dependency into pom.xml:

<plugin>
    <groupId>org.hibernate.orm.tooling</groupId>
    <artifactId>hibernate-enhance-maven-plugin</artifactId>
    <version>${hibernate.version}</version>
    <executions>
        <execution>
            <configuration>
                <failOnError>true</failOnError>
                <enableLazyInitialization>true</enableLazyInitialization>
            </configuration>
            <goals>
                <goal>enhance</goal>
            </goals>
        </execution>
    </executions>
</plugin>

I have checked it in my project and it works, example of entity:

@Entity(name = "processing_record")
public class ProcessingRecord {

/**
 * Why uuid: https://www.clever-cloud.com/blog/engineering/2015/05/20/why-auto-increment-is-a-terrible-idea/
 */
@Id
@Column(name = "record_id")
@org.hibernate.annotations.Type(type = "pg-uuid")
private UUID id;

...

/**
 * Processing result.
 */
@Column(name = "result")
@Basic(fetch = FetchType.LAZY)
private String result;
...

For more details take a look on following article: LINK

Answer 3

From Hibernate, Chapter 19. Improving performance:

Lazy attribute fetching: an attribute or single valued association is fetched when the instance variable is accessed. This approach requires buildtime bytecode instrumentation and is rarely necessary.