Mybatis配置文件resultMap映射啥时候可写可不写？

1、student实体类

public class Student {private Integer id;//编号private String name;//姓名private Double sal;//薪水public Student(){}public Student(Integer id, String name, Double sal) {this.id = id;this.name = name;this.sal = sal;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Double getSal() {return sal;}public void setSal(Double sal) {this.sal = sal;}
}

2、students表结构 1 字段名与实体类字段名相同

create table students(id  int(5) primary key,name varchar(10),sal double(8,2)
);

2.1、resultMap 映射代码

<mapper namespace="studentNamespace">	<resultMap type="mybatis.hello.Student" id="studentMap"><id property="id" column="id"/><result property="name" column="name"/><result property="sal" column="sal"/></resultMap></mapper>

3、students表结构 2 字段名与实体类字段名不同

create table students(students_id  int(5) primary key,students_name varchar(10),students_sal double(8,2)
);

3.1、resultMap 映射代码

<mapper namespace="studentNamespace">	<resultMap type="mybatis.hello.Student" id="studentMap"><id property="id" column="students_id"/><result property="name" column="students_name"/><result property="sal" column="students_sal"/></resultMap></mapper>

1、可不写

当实体属性与表字段名相同的时候，即上面的1和2的情况，2.1resultMap映射代码可不写。

select时，返回用 resultType

	<select id="findById" parameterType="int" resultType="mybatis.hello.Student">select id,name,sal from students where id = #{id}</select>

2、必须写

当实体属性与表字段名不同的时候，即上面的1和3的情况，3.1resultMap映射代码必须写。

select时，返回用 resultMap

<select id="findById" parameterType="int" resultMap="studentMap">select students_id,students_name,students_salfrom studentswhere students_id = #{xxxxxxxxxxxxxxxxxx}
</select>