hibernate的多对多关联之级联查询与自关联查询

一、级联查询：

实体类：

1、TreeNode.class

package com.five.entity;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class TreeNode {
	/*create table t_hibernate_sys_tree_node
	(
	  tree_node_id int primary key auto_increment,                                                 -- ID
	  tree_node_name varchar(50) not null,                                                         -- 名字
	  tree_node_type int not null check(tree_node_type = 1 or tree_node_type = 2),                 -- 节点类型：1 枝节点 2 叶节点

	  position int,                                                                             -- 位置
	  parent_node_id int,                                                                         -- 父节点ID
	  url varchar(1024),                                                                           -- URL
	  foreign key(parent_node_id) references t_hibernate_sys_tree_node(tree_node_id)
	);*/
	
	private Integer treeNodeId;
	private String treeNodeName;
	private Integer treeNodeType;
	private Integer position;
	private String url;
	
	//当前节点与子节点的关联关系	一对多
//	private Set children = new HashSet<>();
	private List children = new ArrayList<>();
	//当前节点与父节点			多对一
	private TreeNode parent;
	private Integer initChildren = 0;
	
/*	public Set getChildren() {
		return children;
	}
	public void setChildren(Set children) {
		this.children = children;
	}*/
	public TreeNode getParent() {
		return parent;
	}
	public List getChildren() {
		return children;
	}
	public void setChildren(List children) {
		this.children = children;
	}
	public void setParent(TreeNode parent) {
		this.parent = parent;
	}
	public Integer getInitChildren() {
		return initChildren;
	}
	public void setInitChildren(Integer initChildren) {
		this.initChildren = initChildren;
	}
	public Integer getTreeNodeId() {
		return treeNodeId;
	}
	public void setTreeNodeId(Integer treeNodeId) {
		this.treeNodeId = treeNodeId;
	}
	public String getTreeNodeName() {
		return treeNodeName;
	}
	public void setTreeNodeName(String treeNodeName) {
		this.treeNodeName = treeNodeName;
	}
	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;
	}
	@Override
	public String toString() {
		return "TreeNode [treeNodeId=" + treeNodeId + ", treeNodeName=" + treeNodeName + ", treeNodeType="
				+ treeNodeType + ", position=" + position + ", url=" + url + ", children=" + children + "]";
	}
}

2、Book.class

package com.five.entity;
import java.util.HashSet;
import java.util.Set;

public class Book {
	/*create table t_hibernate_book
	(
	   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 Set getCategories() {
		return categories;
	}
	public void setCategories(Set categories) {
		this.categories = categories;
	}
	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;
	}
}

3、Category.class

package com.five.entity;

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

public class Category {
	/*create table t_hibernate_category
	(
	   category_id int primary key auto_increment,
	   category_name varchar(50) not null
	);*/
	
	private Integer categoryId;
	private String categoryName;
	private Set books = new HashSet<>();
	private Integer initBooks = 0;
	
	public Integer getInitBooks() {
		return initBooks;
	}
	public void setInitBooks(Integer initBooks) {
		this.initBooks = initBooks;
	}
	public Set getBooks() {
		return books;
	}
	public void setBooks(Set books) {
		this.books = books;
	}
	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;
	}
}

xml映射文件：

1、TreeNode.hbm.xml

2、Book.bhm.xml

3、Category.hbm.xml:

Dao类：

1、TreeNodeDao.class

package com.five.dao;

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

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

public class TreeNodeDao {
	public TreeNode get(TreeNode treeNode) {
		Session session = SessionFactoryUtil.getSession();
		Transaction transaction = session.beginTransaction();
		TreeNode tn = session.get(TreeNode.class, treeNode.getTreeNodeId());
		if(tn != null && new Integer(1).equals(treeNode.getInitChildren())) {
			Hibernate.initialize(tn.getChildren());
		}
		transaction.commit();
		session.close();
		return tn;
	}
}

2、BookDao.class

package com.five.dao;

import java.io.Serializable;

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

import com.five.entity.Book;
import com.two.util.SessionFactoryUtil;

public class BookDao {
	public Book get(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;
	}

3、CategoryDao.class

package com.five.dao;

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

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

public class CategoryDao {
	public Category get(Category category) {
		Session session = SessionFactoryUtil.getSession();
		Transaction transaction = session.beginTransaction();
		Category c = session.get(Category.class, category.getCategoryId());
		if(c != null && new Integer(1).equals(category.getInitBooks())) {
			Hibernate.initialize(c.getBooks());
		}
		transaction.commit();
		session.close();
		return c;
	}
}

JUnit测试类：

1、TreeNodeDaoTest.class

package com.five.dao;

import static org.junit.Assert.*;

import org.junit.Before;
import org.junit.Test;

import com.five.entity.TreeNode;

public class TreeNodeDaoTest {
	
	private TreeNodeDao treeNodeDao = new TreeNodeDao();

	@Test
	public void testGet() {
		/**
		*自关联查询
		*/
		TreeNode treeNode = new TreeNode();
		treeNode.setTreeNodeId(1);
		treeNode.setInitChildren(1);
		TreeNode tn = this.treeNodeDao.get(treeNode);
		System.out.println(tn.getTreeNodeId()+","+tn.getTreeNodeName());
		for (TreeNode tn2 : tn.getChildren()) {
			System.out.println(tn2.getTreeNodeId()+","+tn2.getTreeNodeName());
		}
	}
}

2、BookDaoTest.class

package com.five.dao;

import static org.junit.Assert.*;

import org.junit.Before;
import org.junit.Test;

import com.five.entity.Book;
import com.five.entity.Category;

public class BookDaoTest {
	
	private BookDao bookDao = new BookDao();
	private CategoryDao categoryDao = new CategoryDao();
	 
	/**
	 * 通过一本书能够查询到多个类别
	 * jdbc:三表联查
	 * hibernate:只需要查询单个对象即可，它会自动关联查询，交给映射文件即可
	 */
	
	@Test
	public void testGet1() {
		Book book = new Book();
		book.setBookId(5);
		book.setInitCategories(1);
		Book b = this.bookDao.get(book);
		System.out.println(b.getBookName());
		for (Category c : b.getCategories()) {
			System.out.println(c.getCategoryName());
		}
	}
	
	/**
	 * 通过一个类别查询多个书籍
	 */
	
	@Test
	public void testGet2() {
		Category category = new Category();
		category.setCategoryId(2);
		category.setInitBooks(1);
		Category c = this.categoryDao.get(category);
		System.out.println(c.getCategoryName());
		for (Book b : c.getBooks()) {
			System.out.println(b.getBookName());
		}
	}
}

级联查询总结：
当加载一级节点的时候没问题
加载二级的时候，由于设置了强韧加载，同样可以加载所有的二级节点。没问题
加载三级节点，这时session关闭了，并且默认查出来的节点，是默认采用的是懒加载权限菜单加载有两种方式
1、一次性将数据库表中的数据全部加载往浏览器返回（适用于菜单较少）
2、菜单表数据量较大，点出息浏览器卡顿的情况，第一种方式就不再使用了。
那么咱们就采用菜单逐级加载