关联：指的是类之间的引用关系。
（如果类A与类B关联，那么被引用的类B将被定义为类A的属性。）
数据库：主表从表，通过外键关联
类：
class A{
B b；
}
class B{
}
例：order 和 orderItem
第一步：创建实体类
订单Order
package com.pjl.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;
}
}
订单项OrderItem
package com.pjl.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;
}
}
第二步：配置映射文件
Order.hbm.xml
OrderItem.hbm.xml
2.懒加载 第一步：orderDao
package com.pjl.two.dao;
import java.util.Iterator;
import java.util.List;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.pjl.two.entity.Order;
import com.pjl.two.entity.OrderItem;
import com.pjl.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())) {
//强制加载订单o关联的订单项数据
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();
}
}
第二步：orderDaoTest （调用查询方法）
public void testGet() {
Order order = new Order();
order.setOrderId(7);
Order o = this.orderDao.get(order);
System.out.println(o.getOrderNo());
}
注：结果与数据库一致
public void testGet() {
Order order = new Order();
order.setOrderId(7);
Order o = this.orderDao.get(order);
System.out.println(o.getOrderNo());
System.out.println(o.getOrderItems());
}
注：拿到该订单的订单项
3.一对多的自关联 第一步：实体类TreeNode报错：
failed to lazily initialize a collection of role: com.pjl.two.entity.Order.orderItems, could not initialize proxy - no Session
注：lazily懒加载异常错误。订单项在初始化的时候，session已经关闭了
思路：需要强制加载与该订单关联的订单项数据
如：@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());
}解决：
默认为懒加载的原因：
只需要订单表的数据时，也会将订单项表的数据查出来，此时用到的sql语句量是庞大的
所以默认为懒加载，需要订单项时将order实体类的initOrderItems字段改为1即可
package com.pjl.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 + "]";
}
}
第二步：对应映射关系 （TreeNode.hbm.xml）
第三步：TreeNodeDao
package com.pjl.two.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.pjl.two.entity.TreeNode;
import com.pjl.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;
}
}
第四步：TreeNodeDaoTest调用方法
package com.pjl.two.dao;
import org.junit.Test;
import com.pjl.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());
}
}
展示效果：
4.多对多的关联 第一步：book实体类package com.pjl.two.entity;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
public class Book implements Serializable{
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();
}
}
第二步： Category
package com.pjl.two.entity;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
public class Category implements Serializable{
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 + "]";
}
}
第三步：BookDao
package com.pjl.two.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.lxy.two.entity.Book;
import com.lxy.two.entity.Category;
import com.lxy.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;
// }
}
展示效果：
Hibernate:
select
order0_.order_id as order_id1_0_0_,
order0_.order_no as order_no2_0_0_
from
t_hibernate_order order0_
where
order0_.order_id=?
Hibernate:
select
orderitems0_.oid as oid4_1_0_,
orderitems0_.order_item_id as order_it1_1_0_,
orderitems0_.order_item_id as order_it1_1_1_,
orderitems0_.product_id as product_2_1_1_,
orderitems0_.quantity as quantity3_1_1_,
orderitems0_.oid as oid4_1_1_
from
t_hibernate_order_item orderitems0_
where
orderitems0_.oid=?
P7
