關聯查詢：

一對一：

兩種方式實現:

1.通過業務擴展的方式進行一對一查詢，新建一個實體類，繼承其中屬性多的一個，然后寫上另一個類中的屬性：

實體類:

?

?映射文件:

1 <!-- 業務擴展的方式進行一對一查詢，創建一個新的實體類繼承屬性多的一方然后重寫屬性少的一方 --> 2 <select id="queryStudentWithOO" parameterType="int" resultType="StudentBusiness"> 3 select * from student s inner join studentcard c on s.sid = c.cid and sid = #{sid} 4 </select>

測試類:

1 //一對一查尋 2 public static void queryStudentWithOO() throws IOException { 3 //讀取配置文件 4 Reader reader = Resources.getResourceAsReader("conf.xml"); 5 //創建sqlSessionFactory 6 SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader); 7 //獲取session 8 SqlSession session = sessionFactory.openSession(); 9 //定位映射文件 10 studentMapper studentMapper = session.getMapper(studentMapper.class); 11 //定位sql語句并執行 12 StudentBusiness studentBusiness = studentMapper.queryStudentWithOO(3); 13 //提交事務 14 session.commit(); 15 System.out.println(studentBusiness); 16 //關閉連接 17 session.close(); 18 }

2.通過ResultMap的方式實現一對一

然后在映射文件中使用association進行對象屬性的映射:

實體類:

配置文件:

1 <select id="queryStudentWithMap" parameterType="int" resultMap="StudentBusiness1"> 2 select * from student s inner join studentcard c on s.sid = c.cid and sid = #{sid} 3 </select> 4 <resultMap type="StudentBusiness" id="StudentBusiness1"> 5 <id property="sid" column="sid"/> 6 <result property="sname" column="sname"/> 7 <result property="age" column="age"/> 8 <result property="sex" column="sex"/> 9 <result property="cid" column="cid"/> 10 <result property="stuInfo" column="stuInfo"/> 11 <association property="address" javaType="Address"> 12 <result property="homeAddress" column="homeaddress"/> 13 <result property="schoolAddress" column="schooladdress"/> 14 </association> 15 </resultMap>

測試類:

1 //一對一查尋，使用ResultMap的方式 2 public static void queryStudentWithMap() throws IOException { 3 //讀取配置文件 4 Reader reader = Resources.getResourceAsReader("conf.xml"); 5 //創建sqlSessionFactory 6 SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader); 7 //獲取session 8 SqlSession session = sessionFactory.openSession(); 9 //定位映射文件 10 studentMapper studentMapper = session.getMapper(studentMapper.class); 11 //定位sql語句并執行 12 StudentBusiness studentBusiness = studentMapper.queryStudentWithMap(3); 13 //提交事務 14 session.commit(); 15 System.out.println(studentBusiness); 16 //關閉連接 17 session.close(); 18 }

2.一對多:

一個班級對應多個學生，應在班級的實體類中定義一個學生的屬性,然后在映射文件中使用collection進行對象屬性集合進行映射:

實體類:

?

配置文件：

1 <!-- 一對多查詢 --> 2 <select id="queryStudentWithOM" parameterType="int" resultMap="Studentclass1"> 3 select * from student s inner join studentclass c on s.cno = c.cno and c.cno = #{cno} 4 </select> 5 6 <resultMap type="StudentClass" id="Studentclass1"> 7 <id property="cno" column="cno"/> 8 <result property="cname" column="cname"/> 9 <!-- 循環集合用collection，屬性值寫集合屬性名，類型寫集合中的元素的類型并且使用的是ofType --> 10 <collection property="students" ofType="student"> 11 <result property="sname" column="sname"/> 12 <result property="age" column="age"/> 13 <result property="sex" column="sex"/> 14 </collection> 15 </resultMap>

測試類:

1 //一對多查尋 2 public static void queryStudentWithOM() throws IOException { 3 //讀取配置文件 4 Reader reader = Resources.getResourceAsReader("conf.xml"); 5 //創建sqlSessionFactory 6 SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader); 7 //獲取session 8 SqlSession session = sessionFactory.openSession(); 9 //定位映射文件 10 studentMapper studentMapper = session.getMapper(studentMapper.class); 11 //定位sql語句并執行 12 StudentClass studentClass = studentMapper.queryStudentWithOM(2); 13 System.out.println(studentClass); 14 //提交事務 15 session.commit(); 16 List<Student> students = studentClass.getStudents(); 17 for (Student student : students) { 18 System.out.print(studentClass.getCno() + "," + studentClass.getCname() + ","); 19 System.out.println(student.getSname()+"," +student.getAge()+"," +student.getSex()); 20 } 21 //關閉連接 22 session.close(); 23 }

?

轉載于:https://www.cnblogs.com/man-tou/p/11345703.html

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