one to one - association ; //單對一,使用association one to many -
collection ; //單對多,使用collectionNested results - column is not necessary ,javaType is necessary !
//使用嵌套結果,column 不是必需的,可是JavaType是必需的;javanested queries - column is necessary ,javaType is not necessary !
//使用嵌套查詢,column是必需的,JavaType不是必須的,子查詢自定義resultType便可!!web
t_student 表擁有屬性 class_id 對應 t_class表 t_idsession
public class Classes { private int id; private String name; private Teacher teacher; private List<Student> list; ... }
<select id="getClass4" parameterType="int" resultMap="getClass4Map"> select * from t_class c,t_student s ,t_teacher where c.c_id = s.class_id and c.t_id = t_teacher.t_id and c.c_id = #{id} </select> <resultMap type="Classes" id="getClass4Map"> <result property="id" column="c_id" javaType="int" jdbcType="INTEGER"/> <result property="name" column="c_name" javaType="string" jdbcType="VARCHAR"/> <!-- here column is not necessary !!!--> <association property="teacher" column="t_id" javaType="Teacher" > <id property="id" column="t_id" javaType="int" jdbcType="INTEGER"/> <result property="name" column="t_name" javaType="string" jdbcType="VARCHAR"/> </association> <!-- here, no column !!! --> <collection property="list" ofType="Student" > <result property="id" column="s_id" javaType="int" jdbcType="INTEGER"/> <result property="name" column="s_name" javaType="string" jdbcType="VARCHAR"/> </collection> </resultMap>
<select id="getClass5" parameterType="int" resultMap="getClass5Map"> select * from t_class c where c.c_id = #{id} </select> <select id="getTeacher" parameterType="int" resultType="Teacher"> select t_id id,t_name name from t_teacher where t_id = #{id} </select> <select id="getStudent" parameterType="int" resultType="Student"> select s_id id,s_name name from t_student t where t.class_id = #{id} </select> <resultMap type="Classes" id="getClass5Map"> <result property="id" column="c_id" javaType="int" jdbcType="INTEGER"/> <result property="name" column="c_name" javaType="string" jdbcType="VARCHAR"/> <!-- here,column is necessary !!! 有屬性select = getTeacher--> <association property="teacher" column="t_id" javaType="Teacher" select="getTeacher"> </association> <!-- here,column is necessary !!! 有屬性select = getStudent --> <collection property="list" ofType="Student" select="getStudent" column="c_id"> </collection> <!-- pay attention to the Query condition of SQL statement t.class_id = #{id} not t.s_id = #{id} !!--> </resultMap>
public static SqlSessionFactory getFactory(){ /* flow the src dir*/ String resource = "mybatis.xml"; /*MybatisUtils.class.getResourceAsStream(resource)----- it's wrong !!!! * please distinguish the two up and down * */ InputStream inputStream = MybatisUtils.class.getClassLoader().getResourceAsStream(resource); SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream); return factory; }
測試方法mybatis
@Test public void testSelect4(){ /*set auto commit ,which equals to the above*/ SqlSession session = MybatisUtils.getFactory().openSession(true); String statement = "com.web.mapper.classMapper.getClass4"; /*return the effect rows*/ Classes classes = session.selectOne(statement, 1); Teacher teacher = classes.getTeacher(); List<Student> list = classes.getList(); System.out.println("result.."+classes+','+classes.getClass()); System.out.println(teacher); System.out.println(list); }
> result..Classes [id=1, list=[Student [id=1, name=stu1], Student [id=2, > name=stu2], Student [id=3, name=stu3]], name=計算機, teacher=Teacher > [id=1, name=李明]],class com.web.model.Classes Teacher [id=1, name=李明] > [Student [id=1, name=stu1], Student [id=2, name=stu2], Student [id=3, > name=stu3]]