hibernate关联关系(多对多)

1. 数据库的多对多
1.1 数据库中不能直接映射多对多
处理：创建一个桥接表(中间表)，将一个多对多关系转换成两个一对多

注1：数据库多表联接查询
永远就是二个表的联接查询

A B C D
t1 C
t2 D
t3

注2：交叉连接
注3：外连接：left(左)/right(右)/full(左右)
主从表：连接条件不成立时，主表记录永远保留，与null匹配

A B AB
select * from A,B,AB WHERE A.aID=AB.aID and b.bid = AB.bid
where
在hibernate中，你只管查询当前表对象即可，
hibernate会自动关联桥表以及关联表查询出关联对象

Book Category Book_category
select * from Book b,Book_category bc,category where b.bid = bc.bid and bc.cid = c.cid
and bid = 2

2. hibernate的多对多
2.1 hibernate可以直接映射多对多关联关系(看作两个一对多)

3. 多对多关系注意事项
3.1 一定要定义一个主控方
3.2 多对多删除
3.2.1 主控方直接删除
3.2.2 被控方先通过主控方解除多对多关系，再删除被控方
3.2.3 禁用级联删除
3.3 关联关系编辑，不需要直接操作桥接表，hibernate的主控方会自动维护

一对多关联关系案例：

实体类

package com.huang.four.entity;

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

public class TreeNode {
    private Integer nodeId;
    private String nodeName;
    private Integer treeNodeType;
    private Integer position;
    private String url;
    private TreeNode parent;
    private Set<TreeNode> children = new HashSet<TreeNode>();
    private Integer initChildren = 0;

    public Integer getNodeId() {
        return nodeId;
    }

    public void setNodeId(Integer nodeId) {
        this.nodeId = nodeId;
    }

    public String getNodeName() {
        return nodeName;
    }

    public void setNodeName(String nodeName) {
        this.nodeName = nodeName;
    }

    public Integer getTreeNodeType() {
        return treeNodeType;
    }

    public void setTreeNodeType(Integer treeNodeType) {
        this.treeNodeType = treeNodeType;
    }

    public Integer getPosition() {
        return position;
    }

    public void setPosition(Integer position) {
        this.position = position;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public TreeNode getParent() {
        return parent;
    }

    public void setParent(TreeNode parent) {
        this.parent = parent;
    }

    public Set<TreeNode> getChildren() {
        return children;
    }

    public void setChildren(Set<TreeNode> children) {
        this.children = children;
    }

    public Integer getInitChildren() {
        return initChildren;
    }

    public void setInitChildren(Integer initChildren) {
        this.initChildren = initChildren;
    }

    @Override
    public String toString() {
        return "TreeNode [nodeId=" + nodeId + ", nodeName=" + nodeName + ", treeNodeType=" + treeNodeType
                + ", position=" + position + ", url=" + url + ", initChildren=" + initChildren + "]";
    }

}

配置实体映射文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.huang.four.entity.TreeNode" table="t_hibernate_sys_tree_node">
        <id name="nodeId" type="java.lang.Integer" column="tree_node_id">
            <generator class="increment" />
        </id>
        <property name="nodeName" type="java.lang.String"
            column="tree_node_name">
        </property>
        <property name="treeNodeType" type="java.lang.Integer"
            column="tree_node_type">
        </property>
        <property name="position" type="java.lang.Integer"
            column="position">
        </property>
        <property name="url" type="java.lang.String"
            column="url">
        </property>

        <many-to-one name="parent" class="com.huang.four.entity.TreeNode" column="parent_node_id"/>

        <set name="children" cascade="save-update" inverse="true">
            <key column="parent_node_id"></key>
            <one-to-many class="com.huang.four.entity.TreeNode"/>
        </set>
    </class>
</hibernate-mapping>

然后用junit测试

TreeNodeDao

package com.huang.four.dao;

import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;

import com.huang.four.entity.TreeNode;
import com.huang.two.util.SessionFactoryUtils;

public class TreeNodeDao {
    public TreeNode load(TreeNode treeNode) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        TreeNode t = session.load(TreeNode.class, treeNode.getNodeId());
        if(t != null && new Integer(1).equals(treeNode.getInitChildren())) {
            Hibernate.initialize(t.getChildren());
            Hibernate.initialize(t.getParent());
        }
        transaction.commit();
        session.close();
        return t;
    }
}

TreeNodeDaoTest

package com.huang.four.dao;

import org.junit.Test;

import com.huang.four.entity.TreeNode;

public class TreeNodeDaoTest {
    private TreeNodeDao treeNodeDao = new TreeNodeDao();

//    @Before
//    public void setUp() throws Exception {
//    }
//
//    @After
//    public void tearDown() throws Exception {
//    }

    @Test
    public void testLoad() {
        TreeNode treeNode = new TreeNode();
        treeNode.setNodeId(6);
        treeNode.setInitChildren(1);

        TreeNode t = this.treeNodeDao.load(treeNode);
        System.out.println(t);
        System.out.println(t.getParent());
        System.out.println(t.getChildren());
    }

}

运行结果：

Hibernate:
    select
        treenode0_.tree_node_id as tree_nod1_6_0_,
        treenode0_.tree_node_name as tree_nod2_6_0_,
        treenode0_.tree_node_type as tree_nod3_6_0_,
        treenode0_.position as position4_6_0_,
        treenode0_.url as url5_6_0_,
        treenode0_.parent_node_id as parent_n6_6_0_
    from
        t_hibernate_sys_tree_node treenode0_
    where
        treenode0_.tree_node_id=?
Hibernate:
    select
        children0_.parent_node_id as parent_n6_6_0_,
        children0_.tree_node_id as tree_nod1_6_0_,
        children0_.tree_node_id as tree_nod1_6_1_,
        children0_.tree_node_name as tree_nod2_6_1_,
        children0_.tree_node_type as tree_nod3_6_1_,
        children0_.position as position4_6_1_,
        children0_.url as url5_6_1_,
        children0_.parent_node_id as parent_n6_6_1_
    from
        t_hibernate_sys_tree_node children0_
    where
        children0_.parent_node_id=?
Hibernate:
    select
        treenode0_.tree_node_id as tree_nod1_6_0_,
        treenode0_.tree_node_name as tree_nod2_6_0_,
        treenode0_.tree_node_type as tree_nod3_6_0_,
        treenode0_.position as position4_6_0_,
        treenode0_.url as url5_6_0_,
        treenode0_.parent_node_id as parent_n6_6_0_
    from
        t_hibernate_sys_tree_node treenode0_
    where
        treenode0_.tree_node_id=?
TreeNode [nodeId=6, nodeName=权限管理, treeNodeType=1, position=6, url=null, initChildren=0]
TreeNode [nodeId=1, nodeName=系统管理, treeNodeType=1, position=1, url=null, initChildren=0]
[TreeNode [nodeId=10, nodeName=用户分配角色, treeNodeType=2, position=10, url=null, initChildren=0], TreeNode [nodeId=11, nodeName=角色授予用户, treeNodeType=2, position=11, url=null, initChildren=0]]

下面是多对多关联

实体类　　

Book

package com.huang.four.entity;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

public class Book implements Serializable{
//    book_id int primary key auto_increment,
//       book_name varchar(50) not null,
//       price float not null
    private Integer bookId;
    private String bookName;
    private Float price;

    private Set<Category> categories = new HashSet<Category>();
    private Integer initCategories = 0;

    public Integer getInitCategories() {
        return initCategories;
    }

    public void setInitCategories(Integer initCategories) {
        this.initCategories = initCategories;
    }

    public Integer getBookId() {
        return bookId;
    }

    public void setBookId(Integer bookId) {
        this.bookId = bookId;
    }

    public String getBookName() {
        return bookName;
    }

    public void setBookName(String bookName) {
        this.bookName = bookName;
    }

    public Float getPrice() {
        return price;
    }

    public void setPrice(Float price) {
        this.price = price;
    }

    public Set<Category> getCategories() {
        return categories;
    }

    public void setCategories(Set<Category> categories) {
        this.categories = categories;
    }

    @Override
    public String toString() {
        return "Book [bookId=" + bookId + ", bookName=" + bookName + ", price=" + price + "]";
    }

    public Book(Integer bookId, String bookName) {
        super();
        this.bookId = bookId;
        this.bookName = bookName;
    }

    public Book() {
        super();
    }

}

实体映射文件　　

Book.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.huang.four.entity.Book" table="t_hibernate_book">
        <cache usage="read-only" region="com.zking.five.entity.Book"/>
        <id name="bookId" type="java.lang.Integer" column="book_id">
            <generator class="increment" />
        </id>
        <property name="bookName" type="java.lang.String"
            column="book_name">
        </property>
        <property name="price" type="java.lang.Float"
            column="price">
        </property>

        <!--
            set标签：
                table:对应的是中间表        没有实体类，意味着靠两张主表对应的映射文件联合管理数据
                name:当前映射文件对应的实体类对应的属性
                cascade:级联新增修改，说白了就是当前实体类对应的表删除能否影响到关联表的数据
                inverse:中间表的数据维护的权利交给对方
            key标签
                column:当前表t_hibernate_book的主键在中间表的列段bid
            many-to-many:
                column:代表中间表对应的除去当前表t_hibernate_book的非主键的中间表列段
                class:cid对应的类

         -->
        <set table="t_hibernate_book_category" name="categories" cascade="save-update" inverse="true">
            <!-- one -->
            <key column="bid"></key>
            <!-- many -->
            <many-to-many column="cid" class="com.huang.four.entity.Category"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

注意一定要在hibernate.hbm.xml中加入以下代码：

<!-- 多对多关联 -->
        <mapping resource="com/huang/four/entity/Book.hbm.xml" />

测试：

BookDao

package com.huang.four.dao;

import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;

import com.huang.four.entity.Book;
import com.huang.four.entity.Category;
import com.huang.two.util.SessionFactoryUtils;

public class BookDao{
    public Integer addBook(Book book) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        Integer bid = (Integer) session.save(book);
        transaction.commit();
        session.close();
        return bid;
    }

    public Integer addCategory(Category category) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        Integer cid = (Integer) session.save(category);
        transaction.commit();
        session.close();
        return cid;
    }

    public Category getCategory(Category category) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        Category c = session.get(Category.class, category.getCategoryId());
        transaction.commit();
        session.close();
        return c;
    }

    public Book getBook(Book book) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        Book b = session.get(Book.class, book.getBookId());
        if (b != null && new Integer(1).equals(book.getInitCategories())) {
            Hibernate.initialize(b.getCategories());
        }
        transaction.commit();
        session.close();
        return b;
    }

    public void delBook(Book book) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        session.delete(book);
        transaction.commit();
        session.close();
    }

    public void delCategory(Category category) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        Category c = session.get(Category.class, category.getCategoryId());
        if(c!=null) {
            for (Book b : c.getBooks()) {
//                通过在被控方通过主控方来解除关联关系，最后被控方再做删除
                b.getCategories().remove(c);
            }
        }
        session.delete(c);
        transaction.commit();
        session.close();
    }
}

BookDaoTest

package com.huang.four.dao;

import org.junit.Test;

import com.huang.four.entity.Book;
import com.huang.four.entity.Category;

public class BookDaoTest {
    private BookDao bookDao = new BookDao();

    @Test
    public void testGetBook() {
        Book book = new Book();
        book.setBookId(8);
        book.setInitCategories(1);
        Book b = this.bookDao.getBook(book );
        System.out.println(b.getBookName());
        System.out.println(b.getCategories());
    }
}

结果：

Hibernate:
    select
        book0_.book_id as book_id1_0_0_,
        book0_.book_name as book_nam2_0_0_,
        book0_.price as price3_0_0_
    from
        t_hibernate_book book0_
    where
        book0_.book_id=?
Hibernate:
    select
        categories0_.bid as bid1_1_0_,
        categories0_.cid as cid2_1_0_,
        category1_.category_id as category1_2_1_,
        category1_.category_name as category2_2_1_
    from
        t_hibernate_book_category categories0_
    inner join
        t_hibernate_category category1_
            on categories0_.cid=category1_.category_id
    where
        categories0_.bid=?
圣墟
[Category [categoryId=8, categoryName=言情], Category [categoryId=9, categoryName=言情2]]

book.hbm.xml inverse=fasle
 category.hbm.xml inverse=true
 数据添加正常
 书籍表、桥接表各新增一条数据



package com.huang.four.dao;




import org.junit.Test;




import com.huang.four.entity.Book;
import com.huang.four.entity.Category;




public class BookDaoTest {
	private BookDao bookDao = new BookDao();


@Test
    public void test1() {
        Book book = new Book();
        book.setBookName("T226");
        book.setPrice(10f);
        Category category = new Category();
        category.setCategoryId(5);
//        直接将category对象加入到新建的book中是错误的，因为此时的category是临时态的，hibernate是不会管理的
//        book.getCategories().add(category);
        Category c = this.bookDao.getCategory(category);

//        c.getBooks().add(book);
        book.getCategories().add(c);
        this.bookDao.addBook(book);
    }


运行结果：


Hibernate:
    select
        category0_.category_id as category1_2_0_,
        category0_.category_name as category2_2_0_
    from
        t_hibernate_category category0_
    where
        category0_.category_id=?
Hibernate:
    select
        max(book_id)
    from
        t_hibernate_book
Hibernate:
    insert
    into
        t_hibernate_book
        (book_name, price, book_id)
    values
        (?, ?, ?)
Hibernate:
    update
        t_hibernate_category
    set
        category_name=?
    where
        category_id=?




book.hbm.xml inverse=true
 category.hbm.xml inverse=true
 只增加书籍表数据
 桥接表不加数据
 原因：双方都没有去维护关系


package com.huang.four.dao;

import org.junit.Test;

import com.huang.four.entity.Book;
import com.huang.four.entity.Category;

public class BookDaoTest {
    private BookDao bookDao = new BookDao();
@Test
    public void test2() {
        Book book = new Book();
        book.setBookName("T226hyc");
        book.setPrice(10f);
        Category category = new Category();
        category.setCategoryId(5);
        Category c = this.bookDao.getCategory(category);

        book.getCategories().add(c);
        this.bookDao.addBook(book);
//        c.getBooks().add(book);
    }

}


结果：


Hibernate:
    select
        category0_.category_id as category1_2_0_,
        category0_.category_name as category2_2_0_
    from
        t_hibernate_category category0_
    where
        category0_.category_id=?
Hibernate:
    select
        max(book_id)
    from
        t_hibernate_book
Hibernate:
    insert
    into
        t_hibernate_book
        (book_name, price, book_id)
    values
        (?, ?, ?)
Hibernate:
    update
        t_hibernate_category
    set
        category_name=?
    where
        category_id=?





原文地址：https://www.cnblogs.com/bf6rc9qu/p/11318014.html
				


				
时间： 2024-08-30 10:42:37 

		


		


	

	
	

		


		
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