hibernate入门三：一对多关联关系映射 -

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hibernate入门三：一对多关联关系映射

博客分类：

hibernate

hibernate

实体之间的一对多关系是很常见的一种关联关系，例如：一个人有多套房子，那就有多个地址，一个人在淘宝分不同时段买了多个东西，那就有多个订单；对于在数据库来说，那就是外键的约束关系，多的一方有个字段是外键，指向一的一方。在hibernate中，一对多关联关系映射分为2种，需分情况使用。一种是单向关联关系映射，一种是双向关系映射，下面以2张表说明，表中外键约束通过hibernate维护。下面是表间关系

其去掉foreign key 的SQL为：
CREATE TABLE `ADDRESS` (
`ID` int(4) NOT NULL auto_increment,
`CITY` varchar(40) default NULL,
`STREET` varchar(100) default NULL,
`PERSON_ID` int(4) NOT NULL default '0',
PRIMARY KEY (`ID`)

) ENGINE=MyISAM DEFAULT CHARSET=gb2312;
CREATE TABLE `PERSON` (
`ID` int(4) NOT NULL auto_increment,
`NAME` char(20) default NULL,
`PHONE` char(20) default NULL,
PRIMARY KEY (`ID`)
) ENGINE=MyISAM DEFAULT CHARSET=gb2312;

一对多单向关联关系和一对多双向关联关系数据库表相同，不同的只是映射的JAVA类及映射文件的配置。DAO代码和测试代码省略。
一对多单向关联关系：
实体类：

package com.onetomanysingle.model;

/**
 * Address entity
 */

public class Address implements java.io.Serializable {

	// Fields

	private Integer id;
	private String city;
	private String street;
	private Person person;

	// Constructors

	/** default constructor */
	public Address() {
	}

	/** minimal constructor */
	public Address(Person person) {
		this.person = person;
	}

	/** full constructor */
	public Address(String city, String street, Person person) {
		this.city = city;
		this.street = street;
		this.person = person;
	}

	// Property accessors

	public Integer getId() {
		return this.id;
	}

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

	public String getCity() {
		return this.city;
	}

	public void setCity(String city) {
		this.city = city;
	}

	public String getStreet() {
		return this.street;
	}

	public void setStreet(String street) {
		this.street = street;
	}

	public Person getPerson() {
		return this.person;
	}

	public void setPerson(Person person) {
		this.person = person;
	}

}

package com.onetomanysingle.model;

/**
 * Person entity
 */

public class Person implements java.io.Serializable {

	// Fields

	private Integer id;
	private String name;
	private String phone;

	// Constructors

	/** default constructor */
	public Person() {
	}

	/** full constructor */
	public Person(String name, String phone) {
		this.name = name;
		this.phone = phone;
	}

	// Property accessors

	public Integer getId() {
		return this.id;
	}

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

	public String getName() {
		return this.name;
	}

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

	public String getPhone() {
		return this.phone;
	}

	public void setPhone(String phone) {
		this.phone = phone;
	}

}

映射文件：
Address.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.onetomanysingle.model.Address" table="address" catalog="test">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="city" type="java.lang.String">
            <column name="CITY" length="40" />
        </property>
        <property name="street" type="java.lang.String">
            <column name="STREET" length="100" />
        </property>
        <!-- 映射person到address的一对多单向关联即address到person的多对一单向关联
        具体意义是：通过查询地址可以查询到此地址所住的人（一个）。 -->
        <many-to-one name="person"
                     column="PERSON_ID"
                     class="com.onetomanysingle.model.Person"
                     lazy="false"
                     not-null="true"/>
                     <!-- 以上分别说明映射字段在类中的属性，表中的字段，对应的类，立即加载，非空 -->
    </class>
</hibernate-mapping>

Person.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.onetomanysingle.model.Person" table="person" catalog="test">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" length="20" />
        </property>
        <property name="phone" type="java.lang.String">
            <column name="PHONE" length="20" />
        </property>
    </class>
</hibernate-mapping>

一对多单向关联关系，可以从多的一方查询到一的一方，但从一的一方查询不到多的一方。

一对多双向关联关系映射：
实体类：

package com.onetomanydouble.model;

/**
 * Address entity
 */

public class Address implements java.io.Serializable {

	// Fields

	private Integer id;
	private String city;
	private String street;
	private Person person;

	// Constructors
	public Address() {
		super();
	}

	public Address(Integer id, String city, String street, Person person) {
		super();
		this.id = id;
		this.city = city;
		this.street = street;
		this.person = person;
	}

	// Property accessors

	public Integer getId() {
		return this.id;
	}

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

	public String getCity() {
		return this.city;
	}

	public void setCity(String city) {
		this.city = city;
	}

	public String getStreet() {
		return this.street;
	}

	public void setStreet(String street) {
		this.street = street;
	}

	public Person getPerson() {
		return person;
	}

	public void setPerson(Person person) {
		this.person = person;
	}

}

package com.onetomanydouble.model;

import java.util.HashSet;
import java.util.Set;

/**
 * Person entity
 */

public class Person implements java.io.Serializable {

	// Fields

	private Integer id;
	private String name;
	private String phone;
	private Set address = new HashSet();

	// Constructors

	/** default constructor */
	public Person() {
	}

	public Person(Integer id, String name, String phone, Set address) {
		super();
		this.id = id;
		this.name = name;
		this.phone = phone;
		this.address = address;
	}

	// Property accessors

	public Integer getId() {
		return this.id;
	}

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

	public String getName() {
		return this.name;
	}

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

	public String getPhone() {
		return this.phone;
	}

	public void setPhone(String phone) {
		this.phone = phone;
	}

	public Set getAddress() {
		return address;
	}

	public void setAddress(Set address) {
		this.address = address;
	}

}

映射文件：
Address.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.onetomanydouble.model.Address" table="address" catalog="test">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="city" type="java.lang.String">
            <column name="CITY" length="40" />
        </property>
        <property name="street" type="java.lang.String">
            <column name="STREET" length="100" />
        </property>
       <!-- 多对一映射 -->
       <many-to-one name="person" column="PERSON_ID"
       class="com.onetomanydouble.model.Person"
       lazy="false"
       not-null="true"/>
    </class>
</hibernate-mapping>

Person.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.onetomanydouble.model.Person" table="person" catalog="test">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" length="20" />
        </property>
        <property name="phone" type="java.lang.String">
            <column name="PHONE" length="20" />
        </property>
        <!-- 一对多映射 inverse说明这是主控方，true由被控方(多的一方)维护外键关系，一般来说，都应该由多的一方来维护 -->
        <set name="address" 
        cascade="all"
        inverse="true"
        lazy="false">
        <key column="person_id"/>
        <one-to-many class="com.onetomanydouble.model.Address"/>
        </set>
    </class>
</hibernate-mapping>

一对多双向关联关系，双方均可查询到对方。

从上面可以看出，一对多的单向和双向，只不过是在类中是否有对方作为属性，一的一方有个多的一方的set集合，多的一方有个一的一方做为属性。在配置文件中，单双向多的一方的配置均相同，只有一的一方不同。