Hello everyone,

I was trying to lazy fetch a unidectional one to one mapped object but it failed. Basically I have following two tables:


CREAT TABLE `A` (
`NAME` varchar(128) NOT NULL default '',
`AGE` int(11) default NULL,
PRIMARY KEY (`NAME`),
)

CREATE TABLE B (
`ID` int(11) NOT NULL auto_increment,
`NAME` varchar(128) NOT NULL default '',
`AGE` int(11) default NULL,
PRIMARY KEY (`ID`),
CONSTRAINT BName UNIQUE (`NAME`),
FOREIGN KEY (`NAME`) REFERENCES A(`NAME`) ON DELETE CASCADE
)


The corresponding objects are:



import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

import org.apache.log4j.Logger;
import org.hibernate.Session;
import org.hibernate.Transaction;

import com.fhp.ems.common.data.dao.HibernateInitializer;

@Entity
@Table(name = "A")
public class A {

private String name;
private Integer age;
private B b;


@Id
@Column(name = "NAME", length = 128)
public String getName() {
return this.name;
}


public void setName(String name) {
this.name = name;
}


@Column(name = "AGE")
public Integer getAge() {
return this.age;
}


public void setAge(Integer age) {
this.age = age;
}


@OneToOne(cascade=CascadeType.ALL, fetch = FetchType.LAZY, optional = false)
@JoinColumn(name = "name", referencedColumnName="NAME")
public B getB() {
return b;
}


public void setB(B b) {
this.b = b;
}

}



import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

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

private Integer id;
private String name;



@Id
@Column(name = "ID", unique = true, nullable = false)
public Integer getId() {
return this.id;
}


public void setId(Integer id) {
this.id = id;
}


@Column(name = "NAME", length = 128)
public String getName() {
return this.name;
}


public void setName(String name) {
this.name = name;
}


}



I am expecting that it does a lazy loading. But it actually fetch B using a SELECT query even if I don't call getB() method at all:

Hibernate:
select
a0_.NAME as NAME69_0_,
a0_.AGE as AGE69_0_,
a0_.name as name69_0_
from
A a0_
where
a0_.NAME=?
Hibernate:
select
b0_.ID as ID70_0_,
b0_.NAME as NAME70_0_
from
B b0_
where
b0_.NAME=?

If I change it to FetchType.EAGER, then it does what it is expected - join on B table.


Does anyone know how can I make the lazy loading works? I don't want B is fected until it is used.


Thanks for help.

Hi.,

Try many to one with unique constraint.

I think it should do

Thanks for the quick response. I don't really want to change the one to one relationship if possible, is this the only way to solve this issue?

In that case you have to add the Table B's ID to table A