Mybatis第二章——多表同时插入和级联查询

知识点一：多表同时插入，其中要插入的Blog的数据中的author_id依赖于另一个要插入的author对象的id

此时需要在mapper.xml文件中配置 useGeneratedKeys="true" keyProperty="id"，只需要在被依赖的对象中配置。

insert into tb_author(username,password,email,address,phone) values(#{username},#{password},#{email},#{address},#{phone});

insert into tb_blog(title,content,type,author_id) values(#{title},#{content},#{type},#{author.id});

注意：如果不写useGeneratedKeys=”true” keyProperty=”id”，那么返回给author对象的id将为默认值’0’，

而数据库的author转换成的该条记录可以自增;

useGeneratedKeys的主键自动增长，不是数据库中的数据primary key自动增长，而是让数据库主键匹配到的对象的主键自动增长。

@org.junit.Test

public void test1(){

SqlSessionFactory sqlSessionFactory = MyBatisUtils.getSqlSessionFactory();

SqlSession sqlSession = sqlSessionFactory.openSession();

TestMapper testMapper = sqlSession.getMapper(TestMapper.class);

Author author = new Author("吴健红", "123456", "wjh@163.com", "甘肃", "18888888888");

Blog blog = new Blog("旅游", "去上海旅游", "游玩", author);

testMapper.addAuthor(author);//需要主键生成s

//testMapper.addBlog(blog); 在不使用主键自动增长的情况下，只插入author对象，这样不会报错，从而来测试author对象的id

sqlSession.commit();

System.out.println(author);

sqlSession.close();

//运行结果：Author [id=0, username=吴健红, password=123456, email=wjh@163.com, address=甘肃, phone=18888888888]

知识点二:Mybatis 实现多表查询方式

1.1 业务装配.对两个表编写单表查询语句,在业务(Service)把查询

的两个结果进行关联.

1.2 使用 Auto Mapping 特性,在实现两表联合查询时通过别名完成

映射.

1.3 使用 MyBatis 的标签进行实现.

知识点三：级联一对一的查询(N+1)

N+1 查询方式,先查询出某个表的全部信息,根据这个表的信息

查询另一个表的信息.需要使用到标签

pojo类——Author

package com.xtkj.pojo;

public class Author {

private int id;

private String username;

private String password;

private String email;

private String address;

private String phone;

public Author() {

super();

// TODO Auto-generated constructor stub

}

public Author(String username, String password, String email,

String address, String phone) {

super();

this.username = username;

this.password = password;

this.email - Domain Name For Sale | DAN.COM = email;

this.address = address;

this.phone = phone;

}

@Override

public String toString() {

return "Author [id=" + id + ", username=" + username + ", password="

+ password + ", email=" + email + ", address=" + address

+ ", phone=" + phone + "]";

}

get...

set...

}

pojo类——blog

package com.xtkj.pojo;

import java.util.ArrayList;

import java.util.List;

public class Blog {

private int id;

private String title;

private String content;

private String type;

private Author author;//author_id select * from tb_author where id = author_id;-->author

private List comments = new ArrayList();//id select * from tb_comment where blog_id=id;-->N comment

public Blog() {

super();

// TODO Auto-generated constructor stub

}

public Blog(String title, String content, String type, Author author) {

super();

this.title = title;

this.content = content;

this.type = type;

this.author = author;

}

@Override

public String toString() {

return "Blog [id=" + id + ", title=" + title + ", content=" + content

+ ", type=" + type + ", author=" + author + "]";

}

get...

set...

}

mapper.xml

select * from tb_blog where id=#{id}

select * from tb_author where id=#{id}

大前提使用 N+1 方式.时如果列名和属性名相同可

以不配置,使用 Auto mapping 特性.但是 mybatis 默认只会给列

专配一次

测试

@org.junit.Test

public void test2(){

SqlSessionFactory sqlSessionFactory = MyBatisUtils.getSqlSessionFactory();

SqlSession sqlSession = sqlSessionFactory.openSession();

TestMapper testMapper = sqlSession.getMapper(TestMapper.class);

Blog blog = testMapper.findBlogById(15);

System.out.println(blog);

//sqlSession.commit();

sqlSession.close();

//结果：Blog [id=15, title=旅游, content=去上海旅游, type=游玩, author=Author [id=17, username=吴健红, password=123456, email=wjh@163.com, address=甘肃, phone=18888888888]]

}

知识点四：级联一对多的查询(N+1方式)

mapper.xml

select * from tb_blog where id=#{id}

select * from tb_comment where blog_id=#{blog_id}

测试

@org.junit.Test

public void test3(){

SqlSessionFactory sqlSessionFactory = MyBatisUtils.getSqlSessionFactory();

SqlSession sqlSession = sqlSessionFactory.openSession();

TestMapper testMapper = sqlSession.getMapper(TestMapper.class);

Blog blog = testMapper.findBlogById(15);

System.out.println(blog);

List comments = blog.getComments();

for(int i=0;i

System.out.println("content:"+comments.get(i).getContent());

}

//sqlSession.commit();

sqlSession.close();

}

/*

结果：

Blog [id=15, title=旅游, content=去上海旅游, type=游玩, author=Author [id=17, username=吴健红, password=123456, email=wjh@163.com, address=甘肃, phone=18888888888]]

content:niho

content:lala

*/

知识点五：使用resultMap实现加载集合数据(联合查询方式)

select b.id bid,b.title btitle,b.content bcontent,b.type btype,b.author_id aid,

c.id cid,c.content ccontent from tb_blog b left join tb_comment c on b.id = c.blog_id

where b.id=#{0}

测试

@org.junit.Test

public void test4(){

SqlSessionFactory sqlSessionFactory = MyBatisUtils.getSqlSessionFactory();

SqlSession sqlSession = sqlSessionFactory.openSession();

TestMapper testMapper = sqlSession.getMapper(TestMapper.class);

Blog blog = testMapper.findBlogAndComments(15);

System.out.println(blog);

List comments = blog.getComments();

for(int i=0;i

System.out.println("content:"+comments.get(i).getContent());

}

//sqlSession.commit();

sqlSession.close();

}

/*

结果：

Blog [id=15, title=旅游, content=去上海旅游, type=游玩, author=Author [id=17, username=吴健红, password=123456, email=wjh@163.com, address=甘肃, phone=18888888888]]

content:niho

content:lala

*/