MyBatis笔记----多表关联查询

Posted 2020-09-08 Stay Hungry, Stay Foolish

 

 

 

 

 

 

 

数据库

 

方式一：XML

按照下面类型建立article表

 

Article.java

 

package com.ij34.model;

public class Article {
  private int id;
  private User user;
  private String title;
  private String content;
  
public String getContent() {
    return content;
}
public void setContent(String content) {
    this.content = content;
}
public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public User getUser() {
    return user;
}
public void setUser(User user) {
    this.user = user;
}
public String getTitle() {
    return title;
}
public void setTitle(String title) {
    this.title = title;
}

  
}

 

UserMapper.xml

 颜色aid重点标出部分很重要，必须使用别名，不要最后结果获得article的id全是输入的id

<?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.ij34.mybatis.UserMapper">
  <select id="selectUser" parameterType="int" resultType="com.ij34.model.User">
    select * from users where id=#{id};
  </select>
    <update id="updateUser" keyProperty="id">
    update users set name=#{name},age=#{age} where id=#{id}
  </update>
  
  <insert id="insertUser" >
   insert into users(name,age)values(#{name},#{age})
  </insert>
  <delete id="deleteUser">
    delete from users where name=#{name}
  </delete>
<resultMap type="Article" id="resultAticleList">
  <id property="id" column="aid"/>
  <result property="title" column="title"/>
  <result property="content" column="content"/>
  <association property="user" javaType="User">
  <id property="id" column="id"/>
  <result property="name" column="name"/>
  <result property="age" column="age"/>
  </association>
  </resultMap>
  <select id="selectarticle" parameterType="int" resultMap="resultAticleList">
  select users.id,users.name,users.age,article.id aid,article.title,article.content from users,article
  where users.id=article.userid and users.id=#{id}
  </select>
  </mapper>

 

Test.java

 

package com.ij34.bean;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import com.ij34.model.*;
public class Test {
public static void main(String[] args) throws IOException {
    String resource ="com/ij34/mybatis/mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
   SqlSession session=sqlSessionFactory.openSession();
   try {

       List<Article> articles=session.selectList("com.ij34.mybatis.UserMapper.selectarticle",1);
       for(Article article:articles){
           System.out.println(article.getId()+":"+article.getTitle()+":"+article.getContent()+" "+article.getUser());
       }
} finally {
    // TODO: handle finally clause
   session.close();
}
}
}

 

结果

 

 

方式二：通过接口

 

结构 

 

xml

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<typeAliases>
<typeAlias type="com.ij34.model.User" alias="User"/>
<typeAlias type="com.ij34.model.Article" alias="Article"/>
</typeAliases>
  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true"/>
        <property name="username" value="root"/>
        <property name="password" value="123456"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
  <mapper resource="com/ij34/mybatis/UserMapper.xml"/>
 <!--   <mapper class="com.ij34.model.UserMapper"/> -->
  </mappers>
</configuration>

UserMapper.xml

  <mapper  namespace="com.ij34.model.UserMapper">

   对应于接口UserMapper

<?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.ij34.model.UserMapper">
  <select id="selectUser" parameterType="int" resultType="com.ij34.model.User">
    select * from users where id=#{id};
  </select>
    <update id="updateUser" keyProperty="id">
    update users set name=#{name},age=#{age} where id=#{id}
  </update>
  
  <insert id="insertUser" >
   insert into users(name,age)values(#{name},#{age})
  </insert>
  <delete id="deleteUser">
    delete from users where name=#{name}
  </delete>

  <resultMap type="Article" id="resultAticleList">
  <id property="id" column="aid"/>
  <result property="title" column="title"/>
  <result property="content" column="content"/>
  <association property="user" javaType="User">
  <id property="id" column="id"/>
  <result property="name" column="name"/>
  <result property="age" column="age"/>
  </association>
  </resultMap>
  <select id="selectarticle" parameterType="int" resultMap="resultAticleList">
  select users.id,users.name,users.age,article.id aid,article.title,article.content from users,article
  where users.id=article.userid and users.id=#{id}
  </select>
  </mapper>

 

model

User.java

package com.ij34.model;

public class User {
  private int id;
  private String name;
  private int age;


  public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}
public String toString() {
    return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
}


}

Article.java

package com.ij34.model;

public class Article {
  private int id;
  private User user;
  private String title;
  private String content;
  
public String getContent() {
    return content;
}
public void setContent(String content) {
    this.content = content;
}
public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public User getUser() {
    return user;
}
public void setUser(User user) {
    this.user = user;
}
public String getTitle() {
    return title;
}
public void setTitle(String title) {
    this.title = title;
}

  
}

UserMapper.java

package com.ij34.model;

import java.util.List;

public interface UserMapper {
/*//    @Select("select * from User where id=#{id}")
  public User selectUser(int id);
//    @Update("update User set name=#{name},age=#{age} where id=#{id}")
  public void updateUser(User user);
*/    
    public List<Article> selectarticle(int id);    
}

 

---

 

测试

package com.ij34.bean;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.ij34.model.Article;
import com.ij34.model.UserMapper;

public class Test {
public static void main(String[] args) throws IOException {
    String resource ="com/ij34/mybatis/mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
   SqlSession session=sqlSessionFactory.openSession();
   try {
       UserMapper mapper=session.getMapper(UserMapper.class); 
       List<Article> articles=mapper.selectarticle(1);
       for(Article article:articles){
           System.out.println(article.getId()+":"+article.getTitle()+":"+article.getContent()+" "+article.getUser());
      }
} finally {
    // TODO: handle finally clause
   session.close();
}
}
}

 

结果