Hibernate關係映射

原創 xiaomu709421487 2020-02-24 17:54

1.單向多對一：顧客和訂單例子，一個顧客可以有多個訂單，而一個訂單隻能屬於一個顧客

Customer.java

package com.hibernate.entities.ntoone;

public class Customer {

	private Integer customerId;
	private String customerName;

	public Integer getCustomerId() {
		return customerId;
	}

	public void setCustomerId(Integer customerId) {
		this.customerId = customerId;
	}

	public String getCustomerName() {
		return customerName;
	}

	public void setCustomerName(String customerName) {
		this.customerName = customerName;
	}

}
Order.java 

package com.hibernate.entities.ntoone;

public class Order {
	
	private Integer orderId;
	private String orderName;
	
	private Customer customer;

	public Integer getOrderId() {
		return orderId;
	}

	public void setOrderId(Integer orderId) {
		this.orderId = orderId;
	}

	public String getOrderName() {
		return orderName;
	}

	public void setOrderName(String orderName) {
		this.orderName = orderName;
	}

	public Customer getCustomer() {
		return customer;
	}

	public void setCustomer(Customer customer) {
		this.customer = customer;
	}
	
	
	
}
Customer.hbm.xml 

<?xml version="1.0"?>
<!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.hibernate.entities.ntoone.Customer" table="CUSTOMERS">
    
        <id name="customerId" type="java.lang.Integer">
            <column name="CUSTOMER_ID" />
            <generator class="native" />
        </id>
    
        <property name="customerName" type="java.lang.String">
            <column name="CUSTOMER_NAME" />
        </property>
        
    </class>
    
</hibernate-mapping>
Order.hbm.xml 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hibernate.entities.ntoone">

    <class name="Order" table="ORDERS">

        <id name="orderId" type="java.lang.Integer">
            <column name="ORDER_ID" />
            <generator class="native" />
        </id>
        
        <property name="orderName" type="java.lang.String">
            <column name="ORDER_NAME" />
        </property>
        
		<!-- 
			映射多對一的關聯關係。 使用 many-to-one 來映射多對一的關聯關係 
			name: 多這一端關聯的一那一端的屬性的名字
			class: 一那一端的屬性對應的類名
			column: 一那一端在多的一端對應的數據表中的外鍵的名字
		-->
		<many-to-one name="customer" class="Customer" column="CUSTOMER_ID"></many-to-one>

    </class>
</hibernate-mapping>
還需要把兩個映射文件加入Hibernate的配置文件中。

2.雙向一對多和雙向多對一：是完全相同的兩種情形

雙向一對多需要在一的一端可以訪問多的一端，反之亦然。

Customer.java

package com.hibernate.entities.ntoone.both;

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

public class Customer {

	private Integer customerId;
	private String customerName;
	
	/*
	 * 1. 聲明集合類型時, 需使用接口類型, 因爲 hibernate 在獲取
	 * 集合類型時, 返回的是 Hibernate 內置的集合類型, 而不是 JavaSE 一個標準的
	 * 集合實現. 
	 * 2. 需要把集合進行初始化, 可以防止發生空指針異常
	 */
	private Set<Order> orders = new HashSet<>();

	public Integer getCustomerId() {
		return customerId;
	}

	public void setCustomerId(Integer customerId) {
		this.customerId = customerId;
	}

	public String getCustomerName() {
		return customerName;
	}

	public void setCustomerName(String customerName) {
		this.customerName = customerName;
	}

	public Set<Order> getOrders() {
		return orders;
	}

	public void setOrders(Set<Order> orders) {
		this.orders = orders;
	}
	
	

}
Order.java 

package com.hibernate.entities.ntoone.both;

public class Order {
	
	private Integer orderId;
	private String orderName;
	
	private Customer customer;

	public Integer getOrderId() {
		return orderId;
	}

	public void setOrderId(Integer orderId) {
		this.orderId = orderId;
	}

	public String getOrderName() {
		return orderName;
	}

	public void setOrderName(String orderName) {
		this.orderName = orderName;
	}

	public Customer getCustomer() {
		return customer;
	}

	public void setCustomer(Customer customer) {
		this.customer = customer;
	}
	
	
	
}
Order.hbm.xml 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.atguigu.hibernate.entities.n21.both">

    <class name="Order" table="ORDERS">

        <id name="orderId" type="java.lang.Integer">
            <column name="ORDER_ID" />
            <generator class="native" />
        </id>
        
        <property name="orderName" type="java.lang.String">
            <column name="ORDER_NAME" />
        </property>
        
		<!-- 
			映射多對一的關聯關係。 使用 many-to-one 來映射多對一的關聯關係 
			name: 多這一端關聯的一那一端的屬性的名字
			class: 一那一端的屬性對應的類名
			column: 一那一端在多的一端對應的數據表中的外鍵的名字
		-->
		<many-to-one name="customer" class="Customer" column="CUSTOMER_ID"></many-to-one>

    </class>
</hibernate-mapping>
Customer.hbm.xml 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.atguigu.hibernate.entities.n21.both">
    
    <class name="Customer" table="CUSTOMERS">
    
        <id name="customerId" type="java.lang.Integer">
            <column name="CUSTOMER_ID" />
            <generator class="native" />
        </id>
    
        <property name="customerName" type="java.lang.String">
            <column name="CUSTOMER_NAME" />
        </property>
        
        <!-- 映射 1 對多的那個集合屬性 -->
        <!-- set: 映射 set 類型的屬性, table: set 中的元素對應的記錄放在哪一個數據表中. 該值需要和多對一的多的那個表的名字一致 -->
        <!-- inverse: 指定由哪一方來維護關聯關係. 通常設置爲 true, 以指定由多的一端來維護關聯關係 -->
        <!-- cascade 設定級聯操作. 開發時不建議設定該屬性. 建議使用手工的方式來處理 -->
        <!-- order-by 在查詢時對集合中的元素進行排序, order-by 中使用的是表的字段名, 而不是持久化類的屬性名  -->
        <set name="orders" table="ORDERS" inverse="true" order-by="ORDER_NAME DESC">
        	<!-- 指定多的表中的外鍵列的名字 -->
        	<key column="CUSTOMER_ID"></key>
        	<!-- 指定映射類型 -->
        	<one-to-many class="Order"/>
        </set>
        
    </class>
    
</hibernate-mapping>
還需要將兩個映射文件加入到Hibernate的配置文件中。


3.雙向一對一(單向一對一取一半)

雙向一對一有兩種映射方式：①按照外鍵映射②按照主鍵映射

第一種：按照外鍵映射

Department.java

package com.hibernate.onetoone.foreign;

public class Department {

	private Integer deptId;
	private String deptName;
	
	private Manager mgr;

	public Integer getDeptId() {
		return deptId;
	}

	public void setDeptId(Integer deptId) {
		this.deptId = deptId;
	}

	public String getDeptName() {
		return deptName;
	}

	public void setDeptName(String deptName) {
		this.deptName = deptName;
	}

	public Manager getMgr() {
		return mgr;
	}

	public void setMgr(Manager mgr) {
		this.mgr = mgr;
	}
	
	
	
}

Manager.java 

package com.hibernate.onetoone.foreign;

public class Manager {

	private Integer mgrId;
	private String mgrName;
	
	private Department dept;

	public Integer getMgrId() {
		return mgrId;
	}

	public void setMgrId(Integer mgrId) {
		this.mgrId = mgrId;
	}

	public String getMgrName() {
		return mgrName;
	}

	public void setMgrName(String mgrName) {
		this.mgrName = mgrName;
	}

	public Department getDept() {
		return dept;
	}

	public void setDept(Department dept) {
		this.dept = dept;
	}
	
	
	
}
Department.hbm.xml 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hibernate.onetoone.foreign">

    <class name="Department" table="DEPARTMENTS">

        <id name="deptId" type="java.lang.Integer">
            <column name="DEPT_ID" />
            <generator class="native" />
        </id>
        
        <property name="deptName" type="java.lang.String">
            <column name="DEPT_NAME" />
        </property>
		
		<!-- 使用 many-to-one 的方式來映射 1-1 關聯關係 -->
		<many-to-one name="mgr" class="Manager" 
			column="MGR_ID" unique="true"></many-to-one>	        
			        
    </class>
</hibernate-mapping>

Manager.hbm.xml 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hibernate.onetoone.foreign">

    <class name="Manager" table="MANAGERS">
        
        <id name="mgrId" type="java.lang.Integer">
            <column name="MGR_ID" />
            <generator class="native" />
        </id>
        
        <property name="mgrName" type="java.lang.String">
            <column name="MGR_NAME" />
        </property>
        
        <!-- 映射 1-1 的關聯關係: 在對應的數據表中已經有外鍵了, 當前持久化類使用 one-to-one 進行映射 -->
        <!-- 
        	沒有外鍵的一端需要使用one-to-one元素，該元素使用 property-ref 屬性指定使用被關聯實體主鍵以外的字段作爲關聯字段
         -->
        <one-to-one name="dept" class="Department" property-ref="mgr"></one-to-one>
        
    </class>
    
</hibernate-mapping>
第二種：按照主鍵映射

Department.java

package com.hibernate.onetoone.primary;

public class Department {

	private Integer deptId;
	private String deptName;
	
	private Manager mgr;

	public Integer getDeptId() {
		return deptId;
	}

	public void setDeptId(Integer deptId) {
		this.deptId = deptId;
	}

	public String getDeptName() {
		return deptName;
	}

	public void setDeptName(String deptName) {
		this.deptName = deptName;
	}

	public Manager getMgr() {
		return mgr;
	}

	public void setMgr(Manager mgr) {
		this.mgr = mgr;
	}
	
	
	
}
Manager.java 

package com.hibernate.onetoone.primary;

public class Manager {

	private Integer mgrId;
	private String mgrName;
	
	private Department dept;

	public Integer getMgrId() {
		return mgrId;
	}

	public void setMgrId(Integer mgrId) {
		this.mgrId = mgrId;
	}

	public String getMgrName() {
		return mgrName;
	}

	public void setMgrName(String mgrName) {
		this.mgrName = mgrName;
	}

	public Department getDept() {
		return dept;
	}

	public void setDept(Department dept) {
		this.dept = dept;
	}
	
	
	
}

Department.hbm.xml 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hibernate.onetoone.primary">

    <class name="Department" table="DEPARTMENTS">

        <id name="deptId" type="java.lang.Integer">
            <column name="DEPT_ID" />
            <!-- 使用外鍵的方式來生成當前的主鍵 -->
            <generator class="foreign">
            	<!-- property 屬性指定使用當前持久化類的哪一個屬性的主鍵作爲外鍵 -->
            	<param name="property">mgr</param>
            </generator>
        </id>
        
        <property name="deptName" type="java.lang.String">
            <column name="DEPT_NAME" />
        </property>
		
		<!--  
		採用 foreign 主鍵生成器策略的一端增加 one-to-one 元素映射關聯屬性,
		其 one-to-one 節點還應增加 constrained=true 屬性, 以使當前的主鍵上添加外鍵約束
		-->
		<one-to-one name="mgr" class="Manager" constrained="true"></one-to-one>
					        
    </class>
</hibernate-mapping>
Manager.hbm.xml 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hibernate.onetoone.primary">

    <class name="Manager" table="MANAGERS">
        
        <id name="mgrId" type="java.lang.Integer">
            <column name="MGR_ID" />
            <generator class="native" />
        </id>
        
        <property name="mgrName" type="java.lang.String">
            <column name="MGR_NAME" />
        </property>
        
        <one-to-one name="dept" 
        	class="Department"></one-to-one>
        
    </class>
    
</hibernate-mapping>
4.多對多

①單向多對多

Category.java

package com.hibernate.nton;

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

public class Category {

	private Integer id;
	private String name;
	
	private Set<Item> items = new HashSet<>();

	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 Set<Item> getItems() {
		return items;
	}

	public void setItems(Set<Item> items) {
		this.items = items;
	}
	
	
	
}
Item.java 

package com.hibernate.nton;

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

public class Item {

	private Integer id;
	private String name;
	
	//private Set<Category> categories = new HashSet<>();
	
	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 Set<Category> getCategories() {
		return categories;
	}
	public void setCategories(Set<Category> categories) {
		this.categories = categories;
	}*/
	
	
	
}
Category.hbm.xml 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hibernate.nton">

    <class name="Category" table="CATEGORIES">
    
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
    
        <property name="name" type="java.lang.String">
            <column name="NAME" />
        </property>
        
        <!-- table: 指定中間表 -->
        <set name="items" table="CATEGORIES_ITEMS">
            <key>
                <column name="C_ID" />
            </key>
            <!-- 使用 many-to-many 指定多對多的關聯關係. column 執行 Set 集合中的持久化類在中間表的外鍵列的名稱  -->
            <many-to-many class="Item" column="I_ID"></many-to-many>
        </set>
        
    </class>
</hibernate-mapping>

Item.hbm.xml 

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hibernate.nton">

    <class name="Item" table="ITEMS">
        
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        
        <property name="name" type="java.lang.String">
            <column name="NAME" />
        </property>
        
        <!-- <set name="categories" table="CATEGORIES_ITEMS" inverse="true">
        	<key column="I_ID"></key>
        	<many-to-many class="Category" column="C_ID"></many-to-many>
        </set> -->
        
    </class>
</hibernate-mapping>
②雙向多對多：將上面代碼中的註釋去掉即可。


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