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 class="increment" />
        </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 class="com.crazy.Product"/>
    	</set>
    </class>
</hibernate-mapping>

   与Set映射有点儿像

   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 class="increment" />
        </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 class="increment" />
        </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 class="com.crazy.Product"/>
        </set>
    </class>
</hibernate-mapping>

 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 class="increment" />
        </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 class="com.crazy.Product"/>
 </set>

注意:通常来说，在多对一关联和多对多的关联关系中使用级联没有任何意义。级联通常应用在一对多喝一对一的关联中，应用级联可以少写几行代码；否则需要维护级联的操作，需要多写几行代码。同时，cascade属性的save-update是最为常用的。

• 一对多双向关联  
  

   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, 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 class="increment" />
        </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 class="com.crazy.Product" />
        </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 class="increment" />
        </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" class="com.crazy.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 class="com.crazy.Product" />
</set>