mybatis 一對一、一對多和多對多查詢實例代碼

關鍵字：association 一對一映射（一個班級只有一個班主任）

 <select id="getClass" parameterType="int" resultMap="ClassesResultMap"> select * from class c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id} </select> <resultMap type="com.lcb.user.Classes" id="ClassesResultMap"> <id property="id" column="c_id"/> <result property="name" column="c_name"/> <association property="teacher" javaType="com.lcb.user.Teacher"> <id property="id" column="t_id"/> <result property="name" column="t_name"/> </association> </resultMap>

關鍵字：collection 一對多映射（一個老師有多個學生）

 <resultMap type="Teacher" id="teacherMaps"> <id column="id" property="id"/> <result column="name" property="name"/> <result column="class_name" property="className"/> <collection property="students" ofType="Student" select="getStudents" column="id"> </collection> </resultMap> <!-- 查詢所有的老師級各自的所有學生--> <select id="getAllTeacher" parameterType="Teacher" resultMap="teacherMaps"> SELECT t.id, t.NAME, t.class_name FROM teacher t </select> <select id="getStudents" parameterType="int" resultType="Student"> select s.id, s. NAME, s.class_name as className from student s where teacher_id = #{id} </select>

關鍵字：association 多對一映射（多個人屬於一個國家）

多對一相當於一對多，也可以使用collection

 <select id="selectCountry" resultType="Country"> select cid,cname from country where cid=#{ooo} </select> <resultMap type="People" id="peopleMapper2"> <id column="pid" property="pid"/> <result column="pname" property="pname"/> <association property="country" javaType="Country" select="selectCountry" column="countryId" /> </resultMap> <select id="selectById2" resultMap="peopleMapper2"> select pid,pname,countryId from people where pid = #{xxx} </select>

總結

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