Objectives:
1: Understanding one to many relationships

2: Understand lazy loading and forced loading

3: Understanding one to many autocorrelation

4: Understanding many to many relationships

1, One to many association, lazy loading and forced loading

One to many association configuration (environment: order (1) and order details (many)), lazy loading and forced loading

Entity class, dao layer, xml file and test class to be used

Entity class Order:

package com.dzl.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;
	
	//Note: variable attributes must be accepted by the interface
	private Set<OrderItem> orderItems = new HashSet<>();
	
	private Integer initOrderItems = 0;//0 represents lazy loading and 1 represents forced loading
	
	
	public Integer getInitOrderItems() {
		return initOrderItems;
	}
	public void setInitOrderItems(Integer initOrderItems) {
		this.initOrderItems = initOrderItems;
	}
	public Set<OrderItem> getOrderItems() {
		return orderItems;
	}
	public void setOrderItems(Set<OrderItem> 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;
	}
	
}

Entity class OrderItem:

package com.dzl.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;
	}
	
}

XML file Order.hbm.xml          OrderItem.hbm.xml

Order.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.dzl.two.entity.Order" table="t_hibernate_order">
	<id name="orderId" type="java.lang.Integer" column="order_id">
		<generator class="increment"></generator>
	</id>
	
	<property name="orderNo" type="java.lang.String" column="order_no"/>
	
	<!-- 
		cascade:Cascade attribute configuration
		inverse: Is the relationship maintained by the other party?
	 -->
	<set name="orderItems" cascade="save-update" inverse="true">
		<key column="oid"></key>
		<one-to-many class="com.sg.two.entity.OrderItem"/>
	</set>
</class>
</hibernate-mapping>

OrderItem.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.dzl.two.entity.OrderItem" table="t_hibernate_order_item">
	<id name="orderItemId" type="java.lang.Integer" column="order_item_id">
		<generator class="increment"></generator>
	</id>
	
	<property name="productId" type="java.lang.Integer" column="product_id"/>
	<property name="quantity" type="java.lang.Integer" column="quantity"/>
	<property name="oid" type="java.lang.Integer" column="oid"/>
	
	<!-- Repeated column in mapping for entity: com.zking.four.entity.OrderItem column: oid (should be mapped with insert="false" update="false") -->
	<many-to-one name="order" class="com.sg.two.entity.Order" insert="false" update="false" column="oid"></many-to-one>
	
</class>
</hibernate-mapping>

Test class: OrderDaoTest and dao layer: OrderDao/OrderItemDao

OrderDaoTest:

package com.dzl.two.dao;
 
import java.util.List;
import org.junit.Test;
import com.sg.two.entity.Order;
 
 
public class OrderDaoTest {
	private OrderDao orderDao = new OrderDao();
 
	/**
	 * org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.zking.two.entity.Order.orderItems, could not initialize proxy - no Session
	 * 1.Normal query
	 * 2.Lazy load exception error
	 * 3.performance tuning 
	 */
	@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<Order> 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.dzl.two.dao;
 
import java.util.Iterator;
import java.util.List;
 
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
 
import com.dzl.two.entity.Order;
import com.dzl.two.entity.OrderItem;
import com.dzl.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());
//		In addition, if you want to query the data of associated order items, you can use forced loading
		if(o != null && new Integer(1).equals(order.getInitOrderItems())) {
			Hibernate.initialize(o.getOrderItems());
		}
		
		transaction.commit();
		session.close();
		return o;
	}
	
	public List<Order> list() {
		Session session = SessionFactoryUtil.getSession();
		Transaction transaction = session.beginTransaction();
		List<Order> 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.dzl.two.dao;
 
import org.hibernate.Session;
import org.hibernate.Transaction;
 
import com.dzl.two.entity.OrderItem;
import com.dzl.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;
	}
}

 

 

When our database data is very large, it will occupy a lot of resources, and sometimes we only need to use it

Sometimes the data of the order table and the order details table are needed, so lazy loading will save a lot of time

Code resources, which is a tuning of performance.

2, One to many autocorrelation

Entity class, dao layer, xml file and test class to be used

(simulation environment: tree menu):

One to many self association means that you can have multiple child nodes, but the parent node has only one and is in your own table

Entity class TreeNode:

package com.dzl.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<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 + ", children=" + children + "]";
//	}
 
	@Override
	public String toString() {
		return "TreeNode [nodeId=" + nodeId + ", nodeName=" + nodeName + ", treeNodeType=" + treeNodeType
				+ ", position=" + position + ", url=" + url + "]";
	}
	
 
}

The first is the parent node (there is only one parent node)

The second is a child node (there may be multiple child nodes, so it is wrapped in a collection)

The third is lazy loading (0 is lazy loading and 1 is forced loading)

 TreeNode.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.sg.two.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.sg.two.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.sg.two.entity.TreeNode"/>
		</set>
	</class>
</hibernate-mapping>

< many to one > many to one: multiple child nodes correspond to a parent node

One to many tags are placed in the < set > tag: a parent node corresponds to multiple child nodes

Test class TreeNodeDaoTest:

package com.dzl.two.dao;
 
import org.junit.Test;
 
import com.dzl.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 layer TreeNodeDao:

package com.dzl.two.dao;
 
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
 
import com.dzl.two.entity.TreeNode;
import com.dzl.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;
	}
}

3, Many to many Association

Entity class, dao layer, xml file and test class to be used

Analysis (simulation environment: teachers and their classes):

Many to many can be understood as two one to many:

Just like the above figure, a class can be managed by multiple teachers, and teachers can manage multiple classes

Entity class Book:

package com.dzl.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<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();
	}
	
	
}

Entity Category:

package com.dzl.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<Book> books = new HashSet<Book>();
	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<Book> getBooks() {
		return books;
	}
	public void setBooks(Set<Book> books) {
		this.books = books;
	}
	@Override
	public String toString() {
		return "Category [categoryId=" + categoryId + ", categoryName=" + categoryName + "]";
	}
	
}

In addition to the table structure, the two entity class tables also have set sets to enclose each other, indicating that they can be one to many

XML files: category.hbm.xml, book.hbm.xml

category.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.dzl.two.entity.Category" table="t_hibernate_category">
		<id name="categoryId" type="java.lang.Integer" column="category_id">
			<generator class="increment" />
		</id>
		<property name="categoryName" type="java.lang.String"
			column="category_name">
		</property>
		
		<set table="t_hibernate_book_category" name="books" cascade="save-update" inverse="true">
			<key column="cid"></key>
			<many-to-many column="bid" class="com.sg.two.entity.Book"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

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.sg.two.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>
		
		<!-- 
			table:Intermediate table
			name:Association properties
			inverse:reversal
			key:The primary key of the current table is the foreign key of the intermediate table
			many-to-many:The primary key of the current table finds the foreign key of another table in the intermediate table
		 -->
		
		<set table="t_hibernate_book_category" name="categories" cascade="save-update" inverse="false">
			<!-- one -->
			<key column="bid"></key>
			<!-- many -->
			<many-to-many column="cid" class="com.dzl.two.entity.Category"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

ABCD method book dao:

package com.dzl.two.dao;
 
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
 
import com.dzl.two.entity.Book;
import com.dzl.two.entity.Category;
import com.dzl.two.util.SessionFactoryUtil;
 
 
public class BookDao /*extends BaseDao*/{
	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()) {
//				The accused party cancels the association relationship through the main control party, and finally the accused party deletes it
				b.getCategories().remove(c);
			}
		}
		session.delete(c);
		transaction.commit();
		session.close();
	}
	
	
	/*
	 * hql Explain (need to inherit BaseDao)
	 */
	/**
	 * No code before BaseDao is used
	 * @param book
	 * @param pageBean
	 * @return
	 */
//	public List<Book> 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<Book> list = query.list();
//		transaction.commit();
//		session.close();
//		return list;
//
//	}
	
	/**
	 * Code after using BaseDao
	 * @param book
	 * @param pageBean
	 * @return
	 */
//	public List<Book> list2(Book book, PageBean pageBean) {
//		Session session = SessionFactoryUtil.getSession();
//		Transaction transaction = session.beginTransaction();
//		String hql = "from Book where 1 = 1";
//		Map<String, Object> map = new HashMap<String, Object>();
//
//		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;
//	}
	
	/**
	 * Use native SQL
	 * @param book
	 * @param pageBean
	 * @return
	 */
//	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;
//	}
}

Test class: BookDaoTest:

package com.dzl.two.dao;
 
import org.junit.Test;
 
import com.dzl.two.entity.Book;
import com.dzl.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());
	}
	
	/**
	 * book.hbm.xml	inverse=fasle
	 * category.hbm.xml inverse=true
	 * Data addition is normal
	 * Add a new piece of data to the book table and bridge table respectively
	 */
	@Test
	public void test1() {
		Book book = new Book();
		book.setBookName("bbbb");
		book.setPrice(10f);
		Category category = new Category();
		category.setCategoryId(5);
//		It is wrong to directly add the category object to the new book, because the category is temporary and hibernate will not manage it
//		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
	 * Only add book table data
	 * Bridge table without data
	 * Reason: neither side has maintained the relationship
	 */
	@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);
	}
	
	
}