Hibernate查询一对一关系

Question

I am new to hibernate I created the tables and mappings and I am listing all the rows in my table using the following code.

List places = session.createQuery("FROM Place").list();
for (Iterator iterator = places.iterator(); iterator.hasNext();) {
   Place place = (Place) iterator.next();
   System.out.println("-" + place.getName());
}

This code works fine however, the PLACE table has a one-to-one relationship with ADDRESS table, and this code returns null values for all the rows in the ADDRESS table and prints out:

-null
-null
-null
-343
-223
-122

I only want the rows from the PLACES table. How can I manage this?

Important Note: After Pierre-Henri Toussaint's answer I noticed the generated sql. Hibernate first generates a select query from address, then a select query from place.(When I change the constraint value to false it generates a query for each row for the address table)

Address.hbm.xml:

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.places.general.Address" table="ADDRESS" schema="dbo">
        <id name="placeId" type="java.lang.Integer">
            <column name="PLACE_ID" />
            <generator class="foreign">
                <param name="property">place</param>
            </generator>
        </id>
        <one-to-one name="place" class="com.places.general.Place"
                    constrained="true">
        </one-to-one>
        <property column="PLACE_ADDRESS" length="250" name="placeAddress" type="java.lang.String"/>
        <property column="PHONE" length="50" name="phone" type="java.lang.String"/>
    </class>
</hibernate-mapping>

Place.hbm.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.places.general.Place" table="PLACES" schema="dbo">
        <id column="ID" name="id" type="java.lang.Integer">
            <generator class="identity"/>
        </id>        
        <property column="NAME" length="100" name="name" not-null="true" type="java.lang.String"/>
        <property column="DETAILS" length="200" name="details" type="java.lang.String"/>
    </class>
</hibernate-mapping>

Place.java:

import java.io.Serializable;

public class Place implements Serializable{
    private Integer id;
    private String name;
    private String details;

    public Place() {
    }

    public Place(String name, String details) {
        this.name = name;
        this. details = details;
    }

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getDetails() {
        return details;
    }

    public void setDetails(String details) {
        this. details = details;
    }
}

Answer 1

Make constrained=false.

What this means: Constrained=true means the Place can not exist without Address. If you want to get a place by providing place_id, first Address object should exist. The way to do it would be,

    Address address = (Address) session.load(Address.class, address_id);
    Place place = address.getPlace();

If you make constrained=false, you can,

   Place place = (Place) session.load(Place.class, place_id);

Same applies to createQuery.

Note, if you were using hibernate3, constrained=true should have been working as well.. it doesn't work on hibernate4..

-Maddy

Answer 2

Looks like your mapping needs some changes

In address.hbm.xml

<one-to-one name="place" class="com.places.general.Place" lazy="false" cascade="all"/>

In your place.hbm.xml

<one-to-one name="address" class="com.places.general.Address" constrained="false"/>

Answer 3

Don't know about the constrained keyword, but it seems that a right outer join query is performed.

I would advice to investigate the query by enabling sql output with :

<property name="show_sql">true</property>

From this you can tackle the specific problem.

Answer 4

Your Place entity does not have Address entity.If you want to make one-to-one relationship correctly,please check this out.

Hibernate – One-To-One Example (XML Mapping)