网格产生太多的休眠查询-FetchMode.JOIN不起作用

Question

I'm developing a webapp using Spring MVC and Hibernate. Thing is, that I need to show all my customer's clients, and each client has another entity associated ("Cobrador", I don't know the english translation here, sorry), I'm using JQgrid for such goal. When I execute the grid, I see in the log:

Hibernate: select cliente0_.id as id1_0_, cliente0_.activo as activo2_0_, cliente0_.apellido as apellido3_0_, cliente0_.cobrador as cobrador8_0_, cliente0_.dni as dni4_0_, cliente0_.email as email5_0_, cliente0_.nombre as nombre6_0_, cliente0_.telefono as telefono7_0_ from clientes cliente0_ where cliente0_.activo=1
Hibernate: select cobrador0_.id as id1_1_0_, cobrador0_.activo as activo2_1_0_, cobrador0_.apellido as apellido3_1_0_, cobrador0_.dni as dni4_1_0_, cobrador0_.email as email5_1_0_, cobrador0_.nombre as nombre6_1_0_, cobrador0_.telefono as telefono7_1_0_ from cobradores cobrador0_ where cobrador0_.id=?
Hibernate: select cobrador0_.id as id1_1_0_, cobrador0_.activo as activo2_1_0_, cobrador0_.apellido as apellido3_1_0_, cobrador0_.dni as dni4_1_0_, cobrador0_.email as email5_1_0_, cobrador0_.nombre as nombre6_1_0_, cobrador0_.telefono as telefono7_1_0_ from cobradores cobrador0_ where cobrador0_.id=?
Hibernate: select cobrador0_.id as id1_1_0_, cobrador0_.activo as activo2_1_0_, cobrador0_.apellido as apellido3_1_0_, cobrador0_.dni as dni4_1_0_, cobrador0_.email as email5_1_0_, cobrador0_.nombre as nombre6_1_0_, cobrador0_.telefono as telefono7_1_0_ from cobradores cobrador0_ where cobrador0_.id=?

Basically getting the clients, and then, for each client go gets the associated "cobrador". My Client entity is configured as follow:

@Entity
@Table(name="clientes")
public class Cliente {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;    
private String apellido;
private String nombre;
private int dni;
private String telefono;
private String email;
private boolean activo;
@ManyToOne
@JoinColumn(name="cobrador")
@Fetch(FetchMode.JOIN)
private Cobrador cobrador;

//Contructors, getters and setters
}

BTW: The final hibernate execution is:

@Override
@Transactional
public List<T> getAllFiltering(String filter) { 
    Query q = sessionFactory.getCurrentSession().createQuery("from " + type.getSimpleName() + " " + filter);
    return q.list();
}

Where is and filter is " where activo=true".

Is there anyway to configure this relationship in order to execute only 1 query when loading the grid?

Thanks in advance!

Answer 1

I know it is not very convenient but Hibernate will not use the fetch strategy if you are using an HQL query (IE using the createQuery method). If you want to make it work, you must use the Criteria API or specify the join in the HQL query.

In your case the query might be something like this :

from Cliente c left join fetch c.cobrador

From the Hibernate documentation :

The fetch strategy defined in the mapping document affects:

• retrieval via get() or load()
• retrieval that happens implicitly when an association is navigated
• Criteria queries
• HQL queries if subselect fetching is used

As you can see, the fetch strategy defined doesn't affect HQL queries if JOIN is the fetchMode.