Hibernate generates multiple SQL queries even when I use Left join fetch

Question

I have an interesting problem with hibernate, the model looks like the following:

@NamedQueries({
    @NamedQuery(name = "A.test", query = "SELECT DISTINCT a FROM A a LEFT JOIN FETCH a.pk.b WHERE a.pk.b.pk.c.id = :cId AND a.pk.b.pk.d.id = :dId")
})
@Entity
@Table(name = "AT")
public class A implements Serializable {

    @EmbeddedId
    private APK pk;
}

@Embeddable
public class APK implements Serializable {

    @ManyToOne
    @JoinColumns({@JoinColumn(name = "***", referencedColumnName = "***"),
                  @JoinColumn(name = "***", referencedColumnName = "***")
    })
    private B b;
}

@Entity
@Table(name = "BT")
public class B implements Serializable {

    @EmbeddedId
    private BPK pk;
}


@Embeddable
public class APK implements Serializable {

    @ManyToOne
    @JoinColumn(name = "***", referencedColumnName = "***")
    private C c;

    @ManyToOne
    @JoinColumn(name = "***", referencedColumnName = "***")
    private D d;
}

The problem is that the named query makes additional SQL queries... What is the problem? Thanks!

Steve Lancashire · Accepted Answer · 2012-04-01 13:04:34Z

1

Hibernate eagerly fetches many to one references by default. When selecting for "A" in your named query there are a number of many to one references that will get resolved and these will correspond to the SQL queries you are seeing. This default behaviour of hibernate can be overridden by judicious placement of lazy loading on your many to one annotations, i.e.:

@ManyToOne(fetch=FetchType.LAZY)

answered Apr 1, 2012 at 13:04

Steve Lancashire

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1 Comment

nerd Over a year ago

Thank You! It is working now. But I have read that setting of fetchtype in @ManyToOne association don't has any effect on queries. I think I missed something, so I go back to the manuals. :S

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