MyBatis练习查询所有的一级分类,同时查询二级分类,以及查询二级分类下的所有图书
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一对多
* 查询所有的一级分类,同时查询二级分类,以及查询二级分类下的所有图书
CREATE TABLE category(
cid VARCHAR(32) PRIMARY KEY,
cname VARCHAR(50),
parent_id VARCHAR(32),
`desc` VARCHAR(100)
);
INSERT INTO category(cid,cname,parent_id,`desc`) VALUES('c100','童书','0','一级分类');
INSERT INTO category(cid,cname,parent_id,`desc`) VALUES('c200','电子书','0','一级分类');
INSERT INTO category(cid,cname,parent_id,`desc`) VALUES('c101','中国儿童文学','c100','二级分类');
INSERT INTO category(cid,cname,parent_id,`desc`) VALUES('c102','婴儿读物','c100','二级分类');
INSERT INTO category(cid,cname,parent_id,`desc`) VALUES('c201','武侠小说','c200','二级分类');
INSERT INTO category(cid,cname,parent_id,`desc`) VALUES('c202','侦探推理','c200','二级分类');
CREATE TABLE book(
bid VARCHAR(32) PRIMARY KEY,
title VARCHAR(50),
price DOUBLE(6,2),
author VARCHAR(50),
cid VARCHAR(32)
);
INSERT INTO book(bid,title,price,author,cid) VALUES('b001','学会管自己(歪歪兔独立成长童话)',64.00,'陈梦敏','c101');
INSERT INTO book(bid,title,price,author,cid) VALUES('b002','写给儿童的中国历史',177.50,'陈卫平','c101');
INSERT INTO book(bid,title,price,author,cid) VALUES('b003','小鸡球球触感玩具书',125.00,'[日]入山智','c102');
INSERT INTO book(bid,title,price,author,cid) VALUES('b004','天龙八部',12.00,'金庸','c201');
INSERT INTO book(bid,title,price,author,cid) VALUES('b005','朱贞木短篇小说集(全套装共8册)',103,'朱贞木','c201');
INSERT INTO book(bid,title,price,author,cid) VALUES('b006','笑傲江湖(新修版)一',1200,'金庸','c201');
INSERT INTO book(bid,title,price,author,cid) VALUES('b007','解忧杂货店',19.99,'(日)东野圭吾','c202');
INSERT INTO book(bid,title,price,author,cid) VALUES('b008','三口棺材',8.99,'(美)约翰·迪克森·卡尔','c202');
表结构
核心代码
/*
* 查询所有
* */
@Select("select * from category c ")
@Results(value = {
@Result(property = "cid", column = "cid",id = true),
@Result(property = "cname", column = "cname"),
@Result(property = "parent_id", column = "parent_id"),
@Result(property = "author", column = "author"),
@Result(property = "desc", column = "desc"),
@Result(property="categories" , many=@Many(select="com.czxy.mybatis_0929.mapper.CategoryMapper.selectAll2")
, column="cid"),
@Result(property="books" , many=@Many(select="com.czxy.mybatis_0929.mapper.BookMapper.selectAll")
, column="cid"),
})
public List<Category> selectAll();
/*
* 查询所有
* */
@Select("select * from category where cid =#{parent_id}")
public List<Category> selectAll2(@Param("parent_id")String parent_id);
/**
* 查询所有
* @return
*/
@Select("select * from book")
@Results(value = {
@Result(property = "bid", column = "bid"),
@Result(property = "title", column = "title"),
@Result(property = "price", column = "price"),
@Result(property = "author", column = "author"),
@Result(property = "cid", column = "cid", id = true),
})
public List<Book> selectAll();
运行结果
代码可从Gitee自行下载
https://gitee.com/the_efforts_paid_offf/java.git
参考答案
1.1.1 搭建环境
•项目:day07_mybatis_category_book
1.1.2 JavaBean
•分类Category
@Entity(name = "category")
public class Category {
@Id
private String cid;
@Column(name = "cname")
private String cname;
@Column(name="`desc`")
private String desc;
// 父分类id
@Column(name="parent_id")
private String parentId;
//多对一:多个二级分类 对应 一个一级分类
private Category category;
//一对多:一个一级分类 对应 多个二级分类
private List<Category> categoryList = new ArrayList<>();
•书籍Book
@Entity(name="book")
public class Book {
@Id
private String bid;
@Column(name="title")
private String title;
@Column(name="price")
private Double price;
@Column(name="author")
private String author;
@Column(name="cid")
private String cid;
//多对一:多本书 属于 一个分类
private Category category;
1.1.3 查询所有一级分类
1) 查询指定父分类的所有分类(单表)
•编写功能接口
package com.czxy.ssm.mapper;
import com.czxy.ssm.domain.Category;
import org.apache.ibatis.annotations.Param;
import java.util.List;
/**
* @author 桐叔
* @email liangtong@itcast.cn
*/
public interface CategoryMapper {
/**
* 查询指定父分类的所有分类
* @param parentId
* @return
*/
public List<Category> selectAll(@Param("parentId") String parentId);
}
•编写SQL语句
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.czxy.ssm.mapper.CategoryMapper">
<resultMap id="categoryResultMap" type="category">
<id property="cid" column="cid"></id>
<result property="cname" column="cname"></result>
<result property="desc" column="desc"></result>
<result property="parentId" column="parent_id"></result>
</resultMap>
<select id="selectAll" resultMap="categoryResultMap">
SELECT * FROM category WHERE parent_id = #{parentId}
</select>
</mapper>
•编程测试类
package com.czxy.ssm;
import com.czxy.ssm.domain.Category;
import com.czxy.ssm.mapper.CategoryMapper;
import com.czxy.ssm.utils.MyBatisUtils;
import java.util.List;
/**
* @author 桐叔
* @email liangtong@itcast.cn
*/
public class Test01_XML_SelectAll {
public static void main(String[] args) {
//1 获得mapper
CategoryMapper categoryMapper = MyBatisUtils.getMapper(CategoryMapper.class);
//2 查询所有的一级分类,同时查询二级分类,同时查询关联书籍
List<Category> oneList = categoryMapper.selectAll("0");
for (Category category : oneList) {
System.out.println(category);
}
//3 释放
MyBatisUtils.commitAndclose();
}
}
2) 查询指定父分类的所有分类,含二级分类(多表)
•修改JavaBean(已修改)
•修改XML,配置映射关系
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.czxy.ssm.mapper.CategoryMapper">
<resultMap id="categoryResultMap" type="category">
<id property="cid" column="cid"></id>
<result property="cname" column="cname"></result>
<result property="desc" column="desc"></result>
<result property="parentId" column="parent_id"></result>
<!--一对多:一个一级分类 对应 多个二级分类-->
<collection property="categoryList" column="cid" select="com.czxy.ssm.mapper.CategoryMapper.selectAll"></collection>
</resultMap>
<select id="selectAll" resultMap="categoryResultMap">
SELECT * FROM category WHERE parent_id = #{parentId}
</select>
</mapper>
•修改测试类,方便数据打印
package com.czxy.ssm;
import com.czxy.ssm.domain.Category;
import com.czxy.ssm.mapper.CategoryMapper;
import com.czxy.ssm.utils.MyBatisUtils;
import java.util.List;
/**
* @author 桐叔
* @email liangtong@itcast.cn
*/
public class Test01_XML_SelectAll {
public static void main(String[] args) {
//1 获得mapper
CategoryMapper categoryMapper = MyBatisUtils.getMapper(CategoryMapper.class);
//2 查询所有的一级分类,同时查询二级分类,同时查询关联书籍
List<Category> oneList = categoryMapper.selectAll("0");
// 2.1 打印一级分类
for (Category oneCategory : oneList) {
System.out.println("one: " + oneCategory);
// 2.2 打印二级分类
for (Category twoCategory : oneCategory.getCategoryList()) {
System.out.println("two: " + twoCategory);
}
}
//3 释放
MyBatisUtils.commitAndclose();
}
}
3)查询指定父分类的所有分类,含二级分类,含书籍信息
•编写BookMapper,功能方法selectAll(cid)
package com.czxy.ssm.mapper;
import com.czxy.ssm.domain.Book;
import org.apache.ibatis.annotations.Param;
import java.util.List;
/**
* @author 桐叔
* @email liangtong@itcast.cn
*/
public interface BookMapper {
/**
* 查询指定分类id的所有书籍
* @param categoryId
* @return
*/
public List<Book> selectAll(@Param("categoryId") String categoryId);
}
•编写BookMapper.xml ,实现SQL语句
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.czxy.ssm.mapper.BookMapper">
<select id="selectAll" resultType="book">
SELECT * FROM book WHERE cid = #{categoryId}
</select>
</mapper>
•修改Category,提供 List属性
//一对多:一个二级分类 对应 多个书籍
private List bookList = new ArrayList<>();
•修改CategoryMapper.xml ,关联书籍信息
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.czxy.ssm.mapper.CategoryMapper">
<resultMap id="categoryResultMap" type="category">
<id property="cid" column="cid"></id>
<result property="cname" column="cname"></result>
<result property="desc" column="desc"></result>
<result property="parentId" column="parent_id"></result>
<!--一对多:一个一级分类 对应 多个二级分类-->
<collection property="categoryList" column="cid" select="com.czxy.ssm.mapper.CategoryMapper.selectAll"></collection>
<!--一对多:一个二级分类 对应 多个书籍 -->
<collection property="bookList" column="cid" select="com.czxy.ssm.mapper.BookMapper.selectAll"></collection>
</resultMap>
<select id="selectAll" resultMap="categoryResultMap">
SELECT * FROM category WHERE parent_id = #{parentId}
</select>
</mapper>
•修改测试类,打印书籍信息
package com.czxy.ssm;
import com.czxy.ssm.domain.Book;
import com.czxy.ssm.domain.Category;
import com.czxy.ssm.mapper.CategoryMapper;
import com.czxy.ssm.utils.MyBatisUtils;
import java.util.List;
/**
* @author 桐叔
* @email liangtong@itcast.cn
*/
public class Test01_XML_SelectAll {
public static void main(String[] args) {
//1 获得mapper
CategoryMapper categoryMapper = MyBatisUtils.getMapper(CategoryMapper.class);
//2 查询所有的一级分类,同时查询二级分类,同时查询关联书籍
List<Category> oneList = categoryMapper.selectAll("0"Mybatis练习(一对多:查询所有的一级分类,同时查询二级分类,以及查询二级分类下的所有图书)