Association：处理单一的关联对象 处理单一属性的关联关系
property：注入给员工中哪个属性
select：发送哪一条sql语句
javaType：把sql语句查询出的结果集，封装给哪个类的对象（可以省略）
column：查询员工的结果集中，用哪个列的值作为条件去查询关联的对象
参考一下mapper文件
<?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.ssm.gbq.mapper.CourseMapper">
<resultMap id="BaseResultMap" type="com.ssm.gbq.model.Course">
<id column="id" jdbcType="INTEGER" property="id" />
<result column="className" jdbcType="VARCHAR" property="className" />
<result column="cname" jdbcType="VARCHAR" property="cname" />
<result column="studentId" jdbcType="INTEGER" property="studentId" />
<result column="remark" jdbcType="VARCHAR" property="remark" />
<result column="teacherId" jdbcType="INTEGER" property="teacherId" />
<association column="id" property="teachers" select="selectArrTeacherById" />
</resultMap>
<sql id="Example_Where_Clause">
<where>
<foreach collection="oredCriteria" item="criteria" separator="or">
<if test="criteria.valid">
<trim prefix="(" prefixOverrides="and" suffix=")">
<foreach collection="criteria.criteria" item="criterion">
<choose>
<when test="criterion.noValue">
and ${criterion.condition}
</when>
<when test="criterion.singleValue">
and ${criterion.condition} #{criterion.value}
</when>
<when test="criterion.betweenValue">
and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
</when>
<when test="criterion.listValue">
and ${criterion.condition}
<foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
#{listItem}
</foreach>
</when>
</choose>
</foreach>
</trim>
</if>
</foreach>
</where>
</sql>
<sql id="Update_By_Example_Where_Clause">
<where>
<foreach collection="example.oredCriteria" item="criteria" separator="or">
<if test="criteria.valid">
<trim prefix="(" prefixOverrides="and" suffix=")">
<foreach collection="criteria.criteria" item="criterion">
<choose>
<when test="criterion.noValue">
and ${criterion.condition}
</when>
<when test="criterion.singleValue">
and ${criterion.condition} #{criterion.value}
</when>
<when test="criterion.betweenValue">
and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
</when>
<when test="criterion.listValue">
and ${criterion.condition}
<foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
#{listItem}
</foreach>
</when>
</choose>
</foreach>
</trim>
</if>
</foreach>
</where>
</sql>
<sql id="Base_Column_List">
id, className, cname, studentId, remark, teacherId
</sql>
<select id="selectByExample" parameterType="com.ssm.gbq.model.CourseExample" resultMap="BaseResultMap">
select
<if test="distinct">
distinct
</if>
<include refid="Base_Column_List" />
from t_course
<if test="_parameter != null">
<include refid="Example_Where_Clause" />
</if>
<if test="orderByClause != null">
order by ${orderByClause}
</if>
</select>
<select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultMap="BaseResultMap">
select
<include refid="Base_Column_List" />
from t_course
where id = #{id,jdbcType=INTEGER}
</select>
<delete id="deleteByPrimaryKey" parameterType="java.lang.Integer">
delete from t_course
where id in
<foreach collection="list" item="item" open="(" close=")" separator=",">#{item}</foreach>
</delete>
<delete id="deleteByExample" parameterType="com.ssm.gbq.model.CourseExample">
delete from t_course
<if test="_parameter != null">
<include refid="Example_Where_Clause" />
</if>
</delete>
<insert id="insert" parameterType="com.ssm.gbq.model.Course">
<selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
SELECT LAST_INSERT_ID()
</selectKey>
insert into t_course (className, cname, studentId,
remark, teacherId)
values (#{className,jdbcType=VARCHAR}, #{cname,jdbcType=VARCHAR}, #{studentId,jdbcType=INTEGER},
#{remark,jdbcType=VARCHAR}, #{teacherId,jdbcType=INTEGER})
</insert>
<insert id="insertSelective" parameterType="com.ssm.gbq.model.Course">
<selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
SELECT LAST_INSERT_ID()
</selectKey>
insert into t_course
<trim prefix="(" suffix=")" suffixOverrides=",">
<if test="className != null">
className,
</if>
<if test="cname != null">
cname,
</if>
<if test="studentId != null">
studentId,
</if>
<if test="remark != null">
remark,
</if>
<if test="teacherId != null">
teacherId,
</if>
</trim>
<trim prefix="values (" suffix=")" suffixOverrides=",">
<if test="className != null">
#{className,jdbcType=VARCHAR},
</if>
<if test="cname != null">
#{cname,jdbcType=VARCHAR},
</if>
<if test="studentId != null">
#{studentId,jdbcType=INTEGER},
</if>
<if test="remark != null">
#{remark,jdbcType=VARCHAR},
</if>
<if test="teacherId != null">
#{teacherId,jdbcType=INTEGER},
</if>
</trim>
</insert>
<select id="countByExample" resultType="int">
select count(*) from t_course
<if test="_parameter != null">
<include refid="Query_By_Example_Where_Clause" />
</if>
</select>
<update id="updateByExampleSelective" parameterType="map">
update t_course
<set>
<if test="record.id != null">
id = #{record.id,jdbcType=INTEGER},
</if>
<if test="record.className != null">
className = #{record.className,jdbcType=VARCHAR},
</if>
<if test="record.cname != null">
cname = #{record.cname,jdbcType=VARCHAR},
</if>
<if test="record.studentId != null">
studentId = #{record.studentId,jdbcType=INTEGER},
</if>
<if test="record.remark != null">
remark = #{record.remark,jdbcType=VARCHAR},
</if>
<if test="record.teacherId != null">
teacherId = #{record.teacherId,jdbcType=INTEGER},
</if>
</set>
<if test="_parameter != null">
<include refid="Update_By_Example_Where_Clause" />
</if>
</update>
<update id="updateByExample" parameterType="map">
update t_course
set id = #{record.id,jdbcType=INTEGER},
className = #{record.className,jdbcType=VARCHAR},
cname = #{record.cname,jdbcType=VARCHAR},
studentId = #{record.studentId,jdbcType=INTEGER},
remark = #{record.remark,jdbcType=VARCHAR},
teacherId = #{record.teacherId,jdbcType=INTEGER}
<if test="_parameter != null">
<include refid="Update_By_Example_Where_Clause" />
</if>
</update>
<update id="updateByPrimaryKeySelective" parameterType="com.ssm.gbq.model.Course">
update t_course
<set>
<if test="className != null">
className = #{className,jdbcType=VARCHAR},
</if>
<if test="cname != null">
cname = #{cname,jdbcType=VARCHAR},
</if>
<if test="studentId != null">
studentId = #{studentId,jdbcType=INTEGER},
</if>
<if test="remark != null">
remark = #{remark,jdbcType=VARCHAR},
</if>
<if test="teacherId != null">
teacherId = #{teacherId,jdbcType=INTEGER},
</if>
</set>
where id = #{id,jdbcType=INTEGER}
</update>
<update id="updateByPrimaryKey" parameterType="com.ssm.gbq.model.Course">
update t_course
set className = #{className,jdbcType=VARCHAR},
cname = #{cname,jdbcType=VARCHAR},
studentId = #{studentId,jdbcType=INTEGER},
remark = #{remark,jdbcType=VARCHAR},
teacherId = #{teacherId,jdbcType=INTEGER}
where id = #{id,jdbcType=INTEGER}
</update>
<select id="selectCourseByTeacherId" parameterType="java.lang.Integer" resultType="com.ssm.gbq.model.Course">
select
<include refid="Base_Column_List" />
from t_course where id in (select courseId from t_teacher_course where teacherId = #{teacherId})
</select>
<select id="selectByLimitPage" resultMap="BaseResultMap">
select <include refid="Base_Column_List" />,
(select name from t_teacher where id = t_course.teacherId) as teacherName,
(select name from t_student where id = t_course.studentId) as studentName
from t_course
<if test="_parameter != null">
<include refid="Query_By_Example_Where_Clause" />
</if>
<if test="example.orderByClause != null and example.orderByClause != ''">
order by ${example.orderByClause}
</if>
limit #{offset},#{limit}
</select>
<sql id="Query_By_Example_Where_Clause" >
<trim prefix="WHERE" prefixOverrides="AND|OR" >
<if test="example.name != null and example.name != ''">
or (name like CONCAT('%',CONCAT('${example.name}','%'))
</if>
<if test="example.name != null and example.name != ''">
or cname like CONCAT('%',CONCAT('${example.name}','%')))
</if>
</trim>
</sql>
<select id="selectArrTeacherById" parameterType="java.lang.Integer" resultType="com.ssm.gbq.model.Teacher">
select * from t_teacher where id in (select teacherId from t_teacher_course where courseId = #{id})
</select>
<select id="countToTeacher" resultType="int">
select count(*) from t_teacher_course where courseId = #{courseId}
</select>
<select id="selectToTeacherPage" resultType="com.ssm.gbq.model.Teacher">
select * from t_teacher where id in (select teacherId from t_teacher_course where courseId = #{courseId})
</select>
<select id="countStudent" resultType="int">
select count(*) from t_student where courseId = #{courseId}
</select>
<select id="selectToStudentPage" resultType="com.ssm.gbq.model.Student">
select *,
(SELECT sum(t_student_custom.customNum)/count(t_student_custom.id) from t_student_custom where t_student_custom.studentId = t_student.id) as customNumPj
from t_student where courseId =#{courseId} order by customNumPj desc
</select>
<insert id="courseToTeacher">
insert into t_teacher_course(courseId,teacherId)
values
<foreach collection="teacherIds" index="index" item="item" separator=",">
(#{courseId},#{item})
</foreach>
</insert>
<delete id="delCourseToTeacher" parameterType="java.lang.Integer">
delete from t_teacher_course
where courseId in
<foreach collection="list" item="item" open="(" close=")" separator=",">#{item}</foreach>
</delete>
</mapper>