hibernate之关联关系（多对多）
hibernate 自关联以及多对多：
自关联：用于左侧树的加载
提供项目大体图片：
开始撸代码
提供TreeNodeDao.java
package com.wangcong.four.dao;import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;import com.wangcong.four.entity.TreeNode;
import com.wangcong.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;}
}提供TreeNodeDaoTest.java
package com.wangcong.four.dao;import org.junit.Test;import com.wangcong.four.entity.TreeNode;public class TreeNodeDaoTest {private TreeNodeDao treeNodeDao = new TreeNodeDao();// @Before
// public void setUp() throws Exception {
// }
//
// @After
// public void tearDown() throws Exception {
// }/*** 注意：* 1.这个在vue的后台要用* 2.它只能加载出直系亲属（父子点和子节点）* 既爷爷和孙子加载不出来(最多只支持三级）*/ @Testpublic void testLoad() {TreeNode treeNode = new TreeNode();//权限管理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());}}提供TreeNode,java
package com.wangcong.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 children = new HashSet();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 getChildren() {return children;}public void setChildren(Set 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 + ", children=" + children + "]";
// }@Overridepublic String toString() {return "TreeNode [nodeId=" + nodeId + ", nodeName=" + nodeName + ", treeNodeType=" + treeNodeType+ ", position=" + position + ", url=" + url + "]";}} 提供TreeNode.hgm.xml
以及在hibernate.cfg,xml的配置：
测试结果：
多对多：
提供项目大体图片：
撸代码开始：
Book.java
package com.wangcong.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 nullprivate Integer bookId;private String bookName;private Float price;private Set categories = new HashSet();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 getCategories() {return categories;}public void setCategories(Set categories) {this.categories = categories;}@Overridepublic 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();}} book.hbm.xml
Category.java
package com.wangcong.four.entity;import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;public class Category implements Serializable{
// category_id int primary key auto_increment,
// category_name varchar(50) not nullprivate Integer categoryId;private String categoryName;private Set books = new HashSet();public Integer getCategoryId() {return categoryId;}public void setCategoryId(Integer categoryId) {this.categoryId = categoryId;}public String getCategoryName() {return categoryName;}public void setCategoryName(String categoryName) {this.categoryName = categoryName;}public Set getBooks() {return books;}public void setBooks(Set books) {this.books = books;}@Overridepublic String toString() {return "Category [categoryId=" + categoryId + ", categoryName=" + categoryName + "]";}} category.hbm.xml
BookDao.java
package com.wangcong.four.dao;import java.util.HashMap;
import java.util.List;
import java.util.Map;import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.query.Query;import com.wangcong.four.entity.Book;
import com.wangcong.four.entity.Category;
import com.wangcong.two.util.SessionFactoryUtils;import antlr.StringUtils;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.java
package com.wangcong.four.dao;import org.junit.Test;import com.wangcong.four.entity.Book;
import com.wangcong.four.entity.Category;public class BookDaoTest {private BookDao bookDao = new BookDao();@Testpublic 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());}/*** 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*/@Testpublic void test1() {Book book = new Book();book.setBookName("only老K自传");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);}/*** 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*/@Testpublic void test2() {Book book = new Book();book.setBookName("c");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);}}以及配置文件hibernate.cfg.xml中加入配置：
测试BookDaoTest中的testGetBook方法：
结果如下图：
测试test1
结果成功。
关于inverse问题：
场景一:
将category.hbm.xml配置中的 inverse=“true” 改成 inverse="false"
将book.hbm.xml配置中的 inverse=“false” 改成 inverse="true"
重新测试test1。
结果 t_hibernate_book插入数据成功，而 t_hibernate_category 插入数据失败
问题所在： 维护对象不对(只能false方维护中间表的数据）
更改代码之后Category来维护中间表的数据，但是在方法中是book在维护，导致维护失败
场景二：
将category.hbm.xml配置中的 inverse=“false” 改成 inverse="true"
测试test2。
中间表依旧没数据。
**问题所在：**中间表的数据没人进行维护。
hibernate中多对多的底层查询原理
存在问题：hibernate 做一次查询要用到三次查询，性能很低
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