第八章Hibernate映射多对一关联关系
第八章Hibernate映射多对一关联关系
?多对一单向关联????? 1.表与表之间的关联可以分成一对一，一对多，多对一和多对多
????? 2.网络商城中，一个大的商品分类下，又多个小的商品分类，一个小的商品分类下，又多个商品
?Product类：
public class Product implements java.io.Serializable {private Integer id;private String name;private Double price;private String decription;public Product() {}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 Double getPrice() {return this.price;}public void setPrice(Double price) {this.price = price;}public String getDecription() {return this.decription;}public void setDecription(String decription) {this.decription = decription;}}?Category类：
public class Category implements java.io.Serializable {private Integer id;private String name;private String description;private Set<Product> products = new HashSet<Product>();public Category() {}public Category(String name, String description) {this.name = name;this.description = description;}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 getDescription() {return this.description;}public void setDescription(String description) {this.description = description;}public Set<Product> getProducts() {return products;}public void setProducts(Set<Product> products) {this.products = products;}}? ? Category映射配置：
<?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"><!-- Mapping file autogenerated by MyEclipse Persistence Tools--><hibernate-mapping> <class name="com.crazy.Category" table="CATEGORY" schema="SCOTT"> <id name="id" type="java.lang.Integer"> <column name="ID" precision="8" scale="0" /> <generator /> </id> <property name="name" type="java.lang.String"> <column name="NAME" length="200" /> </property> <property name="description" type="java.lang.String"> <column name="DESCRIPTION" length="4000" /> </property> <set name="products"><key column="category_id"></key><one-to-many name="code"><?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"><!-- Mapping file autogenerated by MyEclipse Persistence Tools--><hibernate-mapping> <class name="com.crazy.Product" table="PRODUCT" schema="SCOTT"> <id name="id" type="java.lang.Integer"> <column name="ID" precision="8" scale="0" /> <generator /> </id> <property name="name" type="java.lang.String"> <column name="NAME" length="200" /> </property> <property name="price" type="java.lang.Double"> <column name="PRICE" precision="6" /> </property> <property name="decription" type="java.lang.String"> <column name="DECRIPTION" length="2000" /> </property> </class></hibernate-mapping>?一对多单向关联
????? Product与Category是多对一的关系，Product对象维护着Category对象的参考，如果由Category对象维护着多个Product对象的管理，就是一对多单向关联。
Product类：
public class Product implements java.io.Serializable {private static final long serialVersionUID = 1L;private Integer id;private String name;private Double price;private String decription;private Category category;public Product() {}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 Double getPrice() {return this.price;}public void setPrice(Double price) {this.price = price;}public String getDecription() {return this.decription;}public void setDecription(String decription) {this.decription = decription;}public Category getCategory() {return category;}public void setCategory(Category category) {this.category = category;}}? Category类：
public class Category implements java.io.Serializable {private static final long serialVersionUID = 1L;private Integer id;private String name;private String description;private Set<Product> products = new HashSet<Product>();public Set<Product> getProducts() {return products;}public void setProducts(Set<Product> products) {this.products = products;}public Category() {}public Category(String name, String description) {this.name = name;this.description = description;}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 getDescription() {return this.description;}public void setDescription(String description) {this.description = description;}}??Category映射配置：
<?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"><!-- Mapping file autogenerated by MyEclipse Persistence Tools--><hibernate-mapping> <class name="com.crazy.Category" table="CATEGORY" schema="SCOTT"> <id name="id" type="java.lang.Integer"> <column name="ID" precision="8" scale="0" /> <generator /> </id> <property name="name" type="java.lang.String"> <column name="NAME" length="200" /> </property> <property name="description" type="java.lang.String"> <column name="DESCRIPTION" length="4000" /> </property> <set name="products"> <key column="category_id"></key><one-to-many name="code"><?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"><!-- Mapping file autogenerated by MyEclipse Persistence Tools--><hibernate-mapping> <class name="com.crazy.Product" table="PRODUCT" schema="SCOTT"> <id name="id" type="java.lang.Integer"> <column name="ID" precision="8" scale="0" /> <generator /> </id> <property name="name" type="java.lang.String"> <column name="NAME" length="200" /> </property> <property name="price" type="java.lang.Double"> <column name="PRICE" precision="6" /> </property> <property name="decription" type="java.lang.String"> <column name="DECRIPTION" length="2000" /> </property> </class></hibernate-mapping>??级联（cascade）
?????? 主动方对执行操作时，被关联对象（被动方）是否同步执行同一操作。
<set name="products" cascade="save-update"> <key column="category_id"></key><one-to-many name="code">public class Category implements java.io.Serializable {private Integer id;private String name;private String description;private Set<Product> products = new HashSet<Product>();public Category() {}public Category(String name, String description, Set<Product> products) {this.name = name;this.description = description;this.products = products;}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 getDescription() {return this.description;}public void setDescription(String description) {this.description = description;}public Set<Product> getProducts() {return this.products;}public void setProducts(Set<Product> products) {this.products = products;}}? Category映射配置：
?
<?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"><!-- Mapping file autogenerated by MyEclipse Persistence Tools--><hibernate-mapping> <class name="com.crazy.Category" table="CATEGORY" schema="SCOTT"> <id name="id" type="java.lang.Integer"> <column name="ID" precision="8" scale="0" /> <generator /> </id> <property name="name" type="java.lang.String"> <column name="NAME" length="200" /> </property> <property name="description" type="java.lang.String"> <column name="DESCRIPTION" length="4000" /> </property> <set name="products" inverse="true" cascade="save-update"> <key> <column name="CATEGORY_ID" precision="8" scale="0" /> </key> <one-to-many /> </set> </class></hibernate-mapping>
? Product类：
public class Product implements java.io.Serializable {private Integer id;private Category category;private String name;private Double price;private String decription;public Product() {}public Integer getId() {return this.id;}public void setId(Integer id) {this.id = id;}public Category getCategory() {return this.category;}public void setCategory(Category category) {this.category = category;}public String getName() {return this.name;}public void setName(String name) {this.name = name;}public Double getPrice() {return this.price;}public void setPrice(Double price) {this.price = price;}public String getDecription() {return this.decription;}public void setDecription(String decription) {this.decription = decription;}}??? Product映射配置：
?
<?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"><!-- Mapping file autogenerated by MyEclipse Persistence Tools--><hibernate-mapping> <class name="com.crazy.Product" table="PRODUCT" schema="SCOTT"> <id name="id" type="java.lang.Integer"> <column name="ID" precision="8" scale="0" /> <generator /> </id> <property name="name" type="java.lang.String"> <column name="NAME" length="200" /> </property> <property name="price" type="java.lang.Double"> <column name="PRICE" precision="6" /> </property> <property name="decription" type="java.lang.String"> <column name="DECRIPTION" length="2000" /> </property> <many-to-one name="category" outer-join="true"> <column name="CATEGORY_ID" precision="8" scale="0" /> </many-to-one> </class></hibernate-mapping>
? 在类的表现上是，我中有你，你中有我。
控制反转（Inverse）????? 在Hibernate中的一对多的单向或者多向关联的情况下，我们可以将"一"方控制权交给"多"方，称为控制反转。
<set name="products" inverse="true"> <key> <column name="CATEGORY_ID" precision="8" scale="0" /> </key> <one-to-many /></set>?
?