mapper.xml文件详解

1：namespace：不能重复的命名空间
2：select:sql语句映射
3：select>id sql语句的独有id
4：select>parmeterType sql语句传入的参数类型
5：select>resultType sql语句返回的参数类型
6：select>resultMap sql语句中的列名与bean中名称不一致时 可以使用resultMap进行定义或者在列名前定义别名

  • select>resultMap=resultMap的id
  • resultMap type的值等于数据库中表对于的bean类
  • resultMap>id定义主键 id>property=你封装的bean中的列名 id>columu是你数据库中表的列名
  • resultMap>result定义非主键
  • resultMap>association(关联) 用于1对1 需要关联的表 property=对应的javabean中的属性 column对应的数据库表中的列名 javaType=关联的javabean返回类型 select 等于嵌套的select语句id
  • resultMap>collection(集合) 用于1对多 property=对应的javabean中的属性 column对应的数据库表中的列名 javaType=关联的javabean返回类型
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<resultMap type="orders" id="orderResultMap">
		<!-- id属性定义主键 -->
		<id property="id" column="order_id" />
		<!-- result属性定义非主键 -->
		<result property="orderNo" column="order_no" />
		<result property="price" column="order_price" />
	</resultMap>
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<?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.mybatis.mapping.class2Mapper">
	<!-- 方式一: 嵌套结果: 使用嵌套结果映射来处理重复的联合结果的子集
	SELECT * FROM class c, teacher t,student s WHERE c.teacher_id=t.t_id AND c.C_id=s.class_id AND c.c_id=1 -->
	<select id="getClassId" parameterType="int"
		resultMap="ClassIdResultMap">
		select * from class,teacher,student where
		class.c_id=student.class_id and
		class.teacher_id=teacher.t_id and
		c_id=#{id};
	</select>
	<resultMap type="Classes" id="ClassIdResultMap">
		<id property="id" column="c_id" />
		<result property="name" column="c_name" />
		<association property="teacher" javaType="Teacher"
			column="teacher_id">
			<id property="id" column="t_id" />
			<result property="name" column="t_name" />
		</association>
		<collection property="students" ofType="Student">
			<id property="id" column="s_id" />
			<result property="name" column="s_name" />
		</collection>
	</resultMap>
	<!-- 方式二：嵌套查询：通过执行另外一个SQL映射语句来返回预期的复杂类型 SELECT * FROM class WHERE c_id=1; 
		SELECT * FROM teacher WHERE t_id=1 //1 是上一个查询得到的teacher_id的值 SELECT * FROM 
		student WHERE class_id=1 //1是第一个查询得到的c_id字段的值 -->
	<select id="getClassById2" parameterType="int"
		resultMap="getClassById2ResultsetMap">
		select * from class where c_id=#{id}
	</select>
	<resultMap type="Classes" id="getClassById2ResultsetMap">
		<id property="id" column="c_id" />
		<result property="name" column="c_name" />
		<association property="teacher" column="teacher_id"
			javaType="Teacher" select="getTeacher2"></association>
		<collection property="students" ofType="Student"
			column="c_id" select="getStudents"></collection>

	</resultMap>
	<select id="getTeacher2" parameterType="int"
		resultType="Teacher">
		select t_id id,t_name name from teacher where t_id=#{id}
	</select>
	<select id="getStudents" parameterType="int"
		resultType="Student">
		select s_id id,s_name name from student where class_id=#{id}
	</select>
</mapper>