十六、ResultMap初体验

当我们的数据库字段和实体类字段没有保持一直时，会发生查询到某些字段为空的情况。

这时，就要用到ResultMap了。

Demo：

1. User表

2. User.java

package org.zx.pojo;

public class User {

  private long id;
  private String name;
  private String password;


  public User() {
  }

  public User(long id, String name, String password) {
    this.id = id;
    this.name = name;
    this.password = password;
  }


  public long getId() {
    return id;
  }

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


  public String getName() {
    return name;
  }

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


  public String getPassword() {
    return password;
  }

  public void setPassword(String password) {
    this.password = password;
  }


  @Override
  public String toString() {
    return "User{" +
            "id=" + id +
            ", name='" + name + '\'' +
            ", password='" + password + '\'' +
            '}';
  }
}

3. UserMapper.java

public interface UserMapper {


    public User getById(Integer id);

}

4. 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="org.zx.mapper.UserMapper">

    <!--id与select中的resultMap属性保持一致-->
    <!--type是指将结果集映射的类型-->
    <resultMap id="userMap" type="User">
        <!--column指代数据库的列，property指代pojo中的属性-->
        <result column="id" property="id" ></result>
        <result column="name" property="name" ></result>
        <result column="pwd" property="password" ></result>
    </resultMap>

    <select id="getById" parameterType="int" resultMap="User">
        select * from `user` where id = #{id};
    </select>


</mapper>

5. 测试类：UserTest.java

public class UserTest {

    @Test
    public void getById(){
        SqlSession sqlSession = MyBaitsUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        User user = userMapper.getById(1);
        System.out.println(user);
        sqlSession.close();
    }
}