前言：今天要分享的知识是hibernate框架的关联关系
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开发工具:eclipse
目录
1、定义：懒加载可以这样理解，只加载某一项东西，其他的东西不会加载
2、操作：在我们进行项目的操作时候，就会想到，当自己把订单的id查出来之后，改订单id下面的对应的订单项会不会也同样出来
1、定义：一对多的自关联就好比做树形菜单的时候，就会出现一个最大的节点，下面会有很多的子节点。
一对多的配置就是一个对应多个，例如：在订单表和订单项表中，一个订单有多个订单项，但是一个订单项只对应一个订单
配置（user.hbm.xml）
实体类：在order中包含了orderitems这个属性，就是实现一对多的路径
package com.zking.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<OrderItem> 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<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;
}
}orderItems
package com.zking.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;
}
}运行结果
OrderItemsDao
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.正常查询
* 2.懒加载异常错误
* 3.性能调优
*/
@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());
}会出现的懒加载错误
代码
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.正常查询
* 2.懒加载异常错误
* 3.性能调优
*/
@Test
public void testGet() {
Order order = new Order();
order.setOrderId(7);
//order.setInitOrderItems(1);强行加载的代码注释
Order o = this.orderDao.get(order);
System.out.println(o.getOrderNo());
System.out.println(o.getOrderItems());
}错误图示
解决办法就是强行加载，或者将下面要执行代码注释掉
实体类
package com.zking.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 + "]";
}
}xml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.zking.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.zking.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.zking.two.entity.TreeNode"/>
</set>
</class>
</hibernate-mapping>Dao方法
package com.zking.two.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.zking.two.entity.TreeNode;
import com.zking.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;
}
}运行结果
例如在老师与班级的关系中，一个老师可能对应着多个班级，而班级会对应这不同的多个任课老师，而一般老师与班级只会建立两张表储存数据，而还会再建立一张中间表，以描述关系，这就构成了多对多的关联关系。
而多对多，以任何一方做参照看来，都是一对一，所以可以将一个多对多关系理解为两个一对多关系，而在hibernate中，也就是双方都有一对多的关联关系。而这里的一对多关系，是和中间表的关系。（中间表不建立实体类）
entity
package com.zking.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();
}
}package com.zking.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 + "]";
}
}dao
package com.zking.two.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.zking.two.entity.Book;
import com.zking.two.entity.Category;
import com.zking.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()) {
// 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();
}
/*
* hql讲解用到（需要继承BaseDao）
*/
/**
* 没有使用BaseDao之前的代码
* @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;
//
// }
/**
* 使用BaseDao之后的代码
* @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;
// }
/**
* 使用原生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;
// }
}配置
运行结果
到这里就结束了，欢迎大佬指点