Hibernate关联关系

Hibernate关联关系

目标：

一：理解一对多的关联

二：理解懒加载与强制加载

三：理解一对多的自关联

四：理解多对多的关联

一：一对多的关联与懒加载、强制加载

一对多的关联配置（环境：订单(1)与订单详情(多)）与懒加载、强制加载

需要用的实体类、dao层、xml文件、测试类

实体类（Order/OrderItem）

Order

package com.sg.two.entity;

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

public class Order {
//	create table t_hibernate_order
//	(
//	  order_id int primary key auto_increment,
//	  order_no varchar(50) not null
//	);
	private Integer orderId;
	private String orderNo;
	
	//注意：变量属性一定用接口进行接受
	private Set orderItems = new HashSet<>();
	
	private Integer initOrderItems = 0;//0代表懒加载，1代表强制加载
	
	
	public Integer getInitOrderItems() {
		return initOrderItems;
	}
	public void setInitOrderItems(Integer initOrderItems) {
		this.initOrderItems = initOrderItems;
	}
	public Set getOrderItems() {
		return orderItems;
	}
	public void setOrderItems(Set orderItems) {
		this.orderItems = orderItems;
	}
	public Integer getOrderId() {
		return orderId;
	}
	public void setOrderId(Integer orderId) {
		this.orderId = orderId;
	}
	public String getOrderNo() {
		return orderNo;
	}
	public void setOrderNo(String orderNo) {
		this.orderNo = orderNo;
	}
	
}

分析：

Order中必须有该有的表结构

 Order中可以有多个订单详情，所以用集合装起来

 设个属性0代表懒加载，1代表强制加载

OrderItem

package com.sg.two.entity;

public class OrderItem {
//	create table t_hibernate_order_item
//	(
//	  order_item_id int primary key auto_increment,
//	  product_id int not null,
//	  quantity int not null,
//	  oid int not null,
//	  foreign key(oid) references t_hibernate_order(order_id)
//	);
	private Integer orderItemId;
	private Integer productId;
	private Integer quantity;
	private Integer oid;
	
	private Order order;
	public Order getOrder() {
		return order;
	}
	public void setOrder(Order order) {
		this.order = order;
	}
	public Integer getOrderItemId() {
		return orderItemId;
	}
	public void setOrderItemId(Integer orderItemId) {
		this.orderItemId = orderItemId;
	}
	public Integer getProductId() {
		return productId;
	}
	public void setProductId(Integer productId) {
		this.productId = productId;
	}
	public Integer getQuantity() {
		return quantity;
	}
	public void setQuantity(Integer quantity) {
		this.quantity = quantity;
	}
	public Integer getOid() {
		return oid;
	}
	public void setOid(Integer oid) {
		this.oid = oid;
	}
	
}

分析：

表结构

订单详情只对应一个订单 

xml文件（Order.hbm.xml/OrderItem.hbm.xml）

Order.hbm.xml

分析：

该标签是一个对应多个

在这就是一个订单对应多个订单详情

OrderItem.hbm.xml

分析：

该标签是多对一

在这意思是多个订单详情对应一个订单

测试类（OrderDaoTest）与dao层（OrderDao/OrderItemDao）

OrderDaoTest

package com.sg.two.dao;

import java.util.List;
import org.junit.Test;
import com.sg.two.entity.Order;


public class OrderDaoTest {
	private OrderDao orderDao = new OrderDao();

	
	@Test
	public void testGet() {
		Order order = new Order();
		order.setOrderId(7);
//		order.setInitOrderItems(1);
		Order o = this.orderDao.get(order);
		System.out.println(o.getOrderNo());
//		System.out.println(o.getOrderItems());
	}
	
	@Test
	public void testList() {
		List list = this.orderDao.list();
		for (Order o : list) {
			System.out.println(o.getOrderNo());
//			System.out.println(o.getOrderItems().size());
		}
	}
	
	@Test
	public void testDelete() {
		Order order = new Order();
		order.setOrderId(6);
		this.orderDao.delete(order);
	}

}

OrderDao

package com.sg.two.dao;

import java.util.Iterator;
import java.util.List;

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

import com.sg.two.entity.Order;
import com.sg.two.entity.OrderItem;
import com.sg.two.util.SessionFactoryUtil;


public class OrderDao {
	public Order get(Order order) {
		Session session = SessionFactoryUtil.getSession();
		Transaction transaction = session.beginTransaction();
		Order o = session.get(Order.class, order.getOrderId());
//		并且想要查询出关联的订单项的数据是，采用强制加载
		if(o != null && new Integer(1).equals(order.getInitOrderItems())) {
			Hibernate.initialize(o.getOrderItems());
		}
		
		transaction.commit();
		session.close();
		return o;
	}
	
	public List list() {
		Session session = SessionFactoryUtil.getSession();
		Transaction transaction = session.beginTransaction();
		List list = session.createQuery("from Order").list();
		for (Order o: list) {
			Hibernate.initialize(o.getOrderItems());
		}
		transaction.commit();
		session.close();
		return list;
	}
	
	public void delete(Order order) {
		Session session = SessionFactoryUtil.getSession();
		Transaction transaction = session.beginTransaction();
		
		Order o = session.get(Order.class, order.getOrderId());
		for(OrderItem oi:o.getOrderItems()) {
			session.delete(oi);
		}
		session.delete(o);
		
		transaction.commit();
		session.close();
	}
}

OrderItemDao

package com.sg.two.dao;

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

import com.sg.two.entity.OrderItem;
import com.sg.two.util.SessionFactoryUtil;

public class OrderItemDao {
	public OrderItem get(OrderItem orderItem) {
		Session session = SessionFactoryUtil.getSession();
		Transaction transaction = session.beginTransaction();
		OrderItem oi = session.get(OrderItem.class, orderItem.getOrderItemId());
		transaction.commit();
		session.close();
		return oi;
	}
}

分析（按方法分析）：

执行后查询结果

当我放开输出查询订单详情时运行

 就会报下面这个错误

原因：懒加载，在执行完上面那个输出时就已经关闭session了，所以会报错

 这个时候把order.setInitOrderItems(1)放开 ，这里是把上面实体类那个属性设为1

当为1的时候会进那个if判断然后将懒加载就会变为强制加载

这个时候再来运行就不会报错了

 注：为什么会有懒加载，并且是默认使用懒加载？

我们来运行这个方法

 可以看到这个方法的for循环中应用的是强制加载

 我们执行可以看到Hibernate编译出了大量的select语句

 那么当我们的数据库数据非常多的时候这就会占用大量的资源，而且有时候我们只需要用到

订单表的数据，有时候需要订单表和订单详情表的数据，那么使用懒加载就会节约大量的代

码资源，这是性能的一个调优。

二：一对多的自关联

需要用的实体类、dao层、xml文件、测试类

分析（模拟环境：树形菜单）：

一对多的自关联是指自己可以有多个子节点，但父节点只有一个，并且是在自己本身的表里

实体类（TreeNode）

 TreeNode

package com.sg.two.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 + "]";
//	}

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

}

分析：

表结构

第一个为父节点（父节点只有一个）

第二个为子节点（子节点可能有多个所以用集合包起来）

第三个为懒加载（0为懒加载，1为强制加载）

xml文件（TreeNode.hbm.xml）

分析：

多对一：多个子节点对应一个父节点

标签里面放着一对多标签：一个父节点对应多个子节点

测试类（TreeNodeDaoTest ）以及dao层（）

测试类（TreeNodeDaoTest ）

package com.sg.two.dao;

import org.junit.Test;

import com.sg.two.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());
	}

}

dao层（TreeNodeDao ）

package com.sg.two.dao;

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

import com.sg.two.entity.TreeNode;
import com.sg.two.util.SessionFactoryUtil;

public class TreeNodeDao {
	public TreeNode load(TreeNode treeNode) {
		Session session = SessionFactoryUtil.getSession();
		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;
	}
}

分析：

测试类将控制懒加载的方式将其设置为强制加载 

 

结果展示：

三：多对多的关联

需要用的实体类、dao层、xml文件、测试类

分析（模拟环境：老师与其管理的班级）：

多对多可以当成是两个一对多来理解

就像上图一样，一个班级可以多个老师进行管理，老师又可以管理多个班级 

实体类（Book/Category）

Book

package com.sg.two.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 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;
	}

	@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();
	}
	
	
}

Category

package com.sg.two.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 null
	private 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;
	}
	@Override
	public String toString() {
		return "Category [categoryId=" + categoryId + ", categoryName=" + categoryName + "]";
	}
	
}

分析：

两个实体类表中除了表结构都有外，也都有set集合包住对方，说明都可以一对多

 

xml文件（category.hbm.xml/book.hbm.xml）

category.hbm.xml

book.hbm.xml

分析：

table:中间表
name:关联属性
inverse:反转（一边为false一边为true）具体下面分析解释
key:当前表的主键在中间表的外键
many-to-many:当前表的主键在中间表查出另一表的外键

dao方法以及测试类

dao方法（BookDao）

package com.sg.two.dao;

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

import com.sg.two.entity.Book;
import com.sg.two.entity.Category;
import com.sg.two.util.SessionFactoryUtil;


public class BookDao {
	public Integer addBook(Book book) {
		Session session = SessionFactoryUtil.getSession();
		Transaction transaction = session.beginTransaction();
		Integer bid = (Integer) session.save(book);
		transaction.commit();
		session.close();
		return bid;
	}
	
	public Integer addCategory(Category category) {
		Session session = SessionFactoryUtil.getSession();
		Transaction transaction = session.beginTransaction();
		Integer cid = (Integer) session.save(category);
		transaction.commit();
		session.close();
		return cid;
	}
	
	public Category getCategory(Category category) {
		Session session = SessionFactoryUtil.getSession();
		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 = SessionFactoryUtil.getSession();
		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 = SessionFactoryUtil.getSession();
		Transaction transaction = session.beginTransaction();
		session.delete(book);
		transaction.commit();
		session.close();
	}
	
	public void delCategory(Category category) {
		Session session = SessionFactoryUtil.getSession();
		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();
	}
	
	
	
	
//	public List list(Book book, PageBean pageBean) {
//		Session session = SessionFactoryUtil.getSession();
//		Transaction transaction = session.beginTransaction();
//		String hql = "from Book where 1 = 1";
//
//		if (StringUtils.isNotBlank(book.getBookName())) {
//			hql += " and bookName like :bookName";
//		}
//
//		Query query = session.createQuery(hql);
//		
//		if (StringUtils.isNotBlank(book.getBookName())) {
//			query.setParameter("bookName", book.getBookName());
//		}
//
//		if (pageBean != null && pageBean.isPagination()) {
//			query.setFirstResult(pageBean.getStartIndex());
//			query.setMaxResults(pageBean.getRows());
//		}
//		List list = query.list();
//		transaction.commit();
//		session.close();
//		return list;
//
//	}
	
	
//	public List list2(Book book, PageBean pageBean) {
//		Session session = SessionFactoryUtil.getSession();
//		Transaction transaction = session.beginTransaction();
//		String hql = "from Book where 1 = 1";
//		Map map = new HashMap();
//
//		if (StringUtils.isNotBlank(book.getBookName())) {
//			hql += " and bookName like :bookName";
//			map.put("bookName", book.getBookName());
//		}
//		List list = super.executeQuery(session, hql, map, pageBean);
//		transaction.commit();
//		session.close();
//		return list;
//	}
	
	
//	public List list3(Book book, PageBean pageBean) {
		String sql = "select b.*,o.* from t_hibernate_book b,t_hibernate_Order o";
//		String sql = "select * from t_hibernate_book";
//		Session session = SessionFactoryUtil.getSession();
//		Transaction transaction = session.beginTransaction();
//		List list = session.createSQLQuery(sql).list();
//		transaction.commit();
//		session.close();
//		return list;
//	}
}

测试类（BookDaoTest）

package com.sg.two.dao;

import org.junit.Test;

import com.sg.two.entity.Book;
import com.sg.two.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());
	}
	
	
	@Test
	public void test1() {
		Book book = new Book();
		book.setBookName("bbbb");
		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);
	}

	
	@Test
	public void test2() {
		Book book = new Book();
		book.setBookName("dddd");
		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);
	}
	
	
}

分析：

解释为什么要一边为false一边为true

一边为false一边为true时

添加”呜呜呜“ 

数据库：

这边中间表维护了

 

 当都为true时

结果：

 

书籍表肯定会添加一条数据

 

但中间表没有维护 

拜拜了各位！！！