• resultMap结果集映射


    resultMap结果集是用来定义sql查询的结果与java对象的映射关系。它主要解决2大问题:

    1)可以解决POJO属性名和表结构的字段名不一致问题(甚至是 不是标准的驼峰命名法)

    2)可以完成高级查询,例如:一对一,一对多,多对多

    其中还有一个比较重要的属性:autoMapping自动映射  默认为true。

    注意:1.如果true,并且列名称和字段名称一致,是可以完成映射。

              2.如果为true,名称不一致,但是符合驼峰命名,但必须开启驼峰命名匹配。

    下面简单介绍一个案列:

    接口:UserMapper.java

    package com.inter;
    
    import java.util.List;
    
    import org.apache.ibatis.annotations.Param;
    
    import com.pojo.User;
    
    public interface UserMapper {
        
    //    查询数据
        public List<User> selectAll();
        
    }

    Mybatis配置文件: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>
          <!-- 加载外部配置文件 -->
          <properties resource="jdbc.properties"></properties>
          
    /* <settings> <!--开启驼峰命名法--> <setting name="mapUnderscoreToCamelCase" value="true"/> </settings> */
    <!-- 起别名 --> <typeAliases> <typeAlias alias="User" type="com.pojo.User"/> </typeAliases> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="${jdbc.driver}"/> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </dataSource> </environment> </environments> <!-- 指定mapper的配置文件 --> <mappers> <mapper resource="UserMapper.xml"/> </mappers> </configuration>

    映射文件:UserMapper.xml

    <?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.inter.UserMapper">
     
        
       <resultMap type="User" id="userResult" autoMapping="true">
               <id property="id" column="id"/>
       </resultMap>
       
       <!-- 查询所有的数据 -->
       <select id="selectAll" resultMap="userResult">
               select * from tb_user
       </select>
       
     </mapper>

    实体类:User.java

    package com.pojo;
    
    public class User {
        private int id;
        private String name;
        private String age;
        private String sex;
        
        
        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 String getAge() {
            return age;
        }
        public void setAge(String age) {
            this.age = age;
        }
        public String getSex() {
            return sex;
        }
        public void setSex(String sex) {
            this.sex = sex;
        }
        @Override
        public String toString() {
            return "User [id=" + id + ", name=" + name + ", age=" + age + ", sex=" + sex + "]";
        }
        
    }

    测试类:

    package com.test;
    
    import static org.junit.Assert.*;
    
    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 org.junit.Before;
    import org.junit.Test;
    
    import com.inter.UserMapper;
    import com.pojo.User;
    
    public class TestMybatisoneTest {
    
         private UserMapper userMapper;
        
         InputStream inputStream;
         SqlSessionFactory sqlSessionFactory;
         SqlSession sqlSession;
        
        
        @Before
        public void setUp() throws Exception {
            
                String resource = "mybatis-config.xml";     
                 
                inputStream = Resources.getResourceAsStream(resource);
                 
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
                 
                sqlSession = sqlSessionFactory.openSession();
                
    //            动态代理实现
                userMapper = sqlSession.getMapper(UserMapper.class);
        }
    
        @Test
        public void test4(){
           
            List<User> list = userMapper.selectAll();
            for (User user : list) {
                System.out.println(user+"   ");
            }
        }
    }
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  • 原文地址:https://www.cnblogs.com/lichangyun/p/9600076.html
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