Mybatis里面的一对多,一对一查询

围绕以下两个表中的数据展开的查询,两个表里面的学号将这个表里面的信息连接起来了

一个学生选了还几门课,这叫一对多,但每个学号只代表的是一个学生,这叫一对一

model

public class Student {   //一个学生每门课程有一个成绩,所以是一对多
	 private Integer id;
	 private String name;
	 private List<Cour> courlist;
	 private String  sex;
	 private Date  birthday;
	 private String major;
	 private String note;
	public Student() {
		super();
	}
	
	public Student(Integer id, String name, List<Cour> courlist, String sex, Date birthday, String major, String note) {
		super();
		this.id = id;
		this.name = name;
		this.courlist = courlist;
		this.sex = sex;
		this.birthday = birthday;
		this.major = major;
		this.note = note;
	}

	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	public List<Cour> getCourlist() {
		return courlist;
	}

	public void setCourlist(List<Cour> courlist) {
		this.courlist = courlist;
	}

	public String getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public Date getBirthday() {
		return birthday;
	}
	public void setBirthday(Date birthday) {
		this.birthday = birthday;
	}
	public String getMajor() {
		return major;
	}
	public void setMajor(String major) {
		this.major = major;
	}
	public String getNote() {
		return note;
	}
	public void setNote(String note) {
		this.note = note;
	}

	@Override
	public String toString() {
		return "Student [id=" + id + ", name=" + name + ", courlist=" + courlist + ", sex=" + sex + ", birthday="
				+ birthday + ", major=" + major + ", note=" + note + "]";
	}
	
	 
	 
}

public class Cour {   //由于每个学生有好几门课程,每门课程都会有一个成绩,每个成绩对应一个学生,一对一
	 private Integer id;
	 private String stu_code;
	 private String cour_code;
	 private Integer degree;
	 private Student student;
	public Cour() {
		super();
	}
	
	public Cour(Integer id, String stu_code, String cour_code, Integer degree, Student student) {
		super();
		this.id = id;
		this.stu_code = stu_code;
		this.cour_code = cour_code;
		this.degree = degree;
		this.student = student;
	}

	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getStu_code() {
		return stu_code;
	}
	public void setStu_code(String stu_code) {
		this.stu_code = stu_code;
	}
	public String getCour_code() {
		return cour_code;
	}
	public void setCour_code(String cour_code) {
		this.cour_code = cour_code;
	}
	public Integer getDegree() {
		return degree;
	}
	public void setDegree(Integer degree) {
		this.degree = degree;
	}

	public Student getStudent() {
		return student;
	}

	public void setStudent(Student student) {
		this.student = student;
	}

	@Override
	public String toString() {
		return "Cour [id=" + id + ", stu_code=" + stu_code + ", cour_code=" + cour_code + ", degree=" + degree
				+ ", student=" + student + "]";
	}
	
	 
	 
}

 映射文件

首先进行的是一对一的查询,根据stu_cour表里面的学号查询student表里面的内容

CourMapper.xml

<mapper namespace="com.mapper.CourMapper">

        <!-- 对象级联 --><!-- 以下都是一对一的关系,通过stu_cour里面的学号,查找student里面的信息 -->
	

		<!-- 第三种 --><!-- 把查询出来的课程表结果放进courlist这个变量里面 --><resultMap type="Cour" id="CourResult2">
			<!-- 有时获取不到主键的时候,写一个<id/> -->
			<id property="id" column="ID"/>
			<association property="student" column="STU_CODE" select="com.mapper.StudentMapper.selectStuByCode"></association>
		</resultMap> <!--  先把学生表里面的那个学号列查出,column里面写查出的student学号那一列CODE,
		property为student表里面的变量名,然后作为参数传进selectCourByCode -->
  <select id="selectCour" resultMap="CourResult2">
 
<!--  第三种方式: --><!-- 直接通过查询学生表,从而查出课程表的内容 --> select * from stu_cour
    
  </select>
	
   	

</mapper>

还有一种方式

<mapper namespace="com.mapper.StudentMapper">

        <resultMap type="Cour" id="courResult"> <!-- type写的是实体类,id是自己定义的名字 -->
    	 <id property="id" column="ID"/> <!--  查出来的表里面的主键,
    	 property里面写的是stu_cour里面的实体类的变量名,column里面写的是数据库表里面的列名 -->
    	 <result property="stu_code" column="STU_CODE"/><!-- 表里面的其他列名 -->
    	<result property="cour_code" column="COUR_CODE"/>
    	<result property="degree" column="DEGREE"/>


                <result property="student.id" column="ID"/> <!--  student实体类变量直接就是.取出来的变量名 -->
    	<result property="student.name" column="NAME"/>  
    	 <result property="student.sex" column="SEX"/>
    	 <result property="student.birthday" column="BIRTHDAY"/>
    	 <result property="student.major" column="MAJOR"/>
    	 <result property="student.note" column="NOTE"/>
    </resultMap>


         <select id="selectCour" resultMap="courResult">

                select * from student s,stu_cour st where s.code = st.stu_code

        </select>

    </mapper>

 另一种

<mapper namespace="com.mapper.StudentMapper">

        <resultMap type="Student" id="stuResult">
		<id property="id" column="ID"/>
		<result property="name" column="NAME"/>  
    	 <result property="sex" column="SEX"/>
    	 <result property="birthday" column="BIRTHDAY"/>
    	 <result property="major" column="MAJOR"/>
    	 <result property="note" column="NOTE"/>
	</resultMap>



                <resultMap type="Cour" id="courResult"> <!-- type写的是实体类,id是自己定义的名字 -->
    	 <id property="id" column="ID"/> <!--  查出来的表里面的主键,
    	 property里面写的是stu_cour里面的实体类的变量名,column里面写的是数据库表里面的列名 -->
    	 <result property="stu_code" column="STU_CODE"/><!-- 表里面的其他列名 -->
    	<result property="cour_code" column="COUR_CODE"/>
    	<result property="degree" column="DEGREE"/>
    	
    	 
    	<association property="student" resultMap="stuResult" />


    <select id="selectCour" resultMap="courResult">

        select * from student s,stu_cour st where s.code = st.stu_code
    </select>

</mapper>

 CourMapper.java

public interface CourMapper {
		List<Cour> selectCour(); /*一对一*/

}

 StudentMapper.java

public interface StudentMapper {
		
		Student selectStuByCode(String code); //根据学号查询信息
		
}

 StudentMapper.xml

<mapper namespace="com.mapper.StudentMapper">

		<select id="selectStuByCode" resultType="Student">  <!-- 一对一 -->
				select * from student s where s.code = #{code}
		</select>

</mapper>

一对多的查询方式,通过student表里面的学号查询各科目的成绩

studentMapper.xml

<mapper namespace="com.mapper.StudentMapper">

        	<!-- 一对多,通过student表里面的学号,查出所有的学生信息 -->
			<resultMap type="Student" id="StuResult">
				<collection property="courlist" column="CODE" select="com.mapper.CourMapper.selectCourByCode"></collection>
			</resultMap>
		<select id="selectStuByCode" resultMap="StuResult">
				select * from student s where s.code = #{code}
		</select>

</mapper>

 studentMapper.java

public interface StudentMapper {
		
		Student selectStuByCode(String code); //根据学号查询信息
		
}

 CourMapper.java

public interface CourMapper {
		
		List<Cour> selectCourByCode(String stu_code); //一对多的情况使用
}

 CourMapper.xml

<mapper namespace="com.mapper.CourMapper">

        	 <select id="selectCourByCode" resultType="Cour">
   	      select * from stu_cour sc where sc.stu_code = #{stu_code}
   	 
   	 </select>

</mapper>

Junitl 测试

class Junit {  //测试

	private SqlSession sqlSession;
	private  StudentMapper stuMapper;
	private CourMapper courMapper;
	@Test
	void test() {
		/*List<Cour> list = courMapper.selectCour(); 一对一条件下查询用的
		for (Cour cour : list) {
			System.out.println(cour);
		}*/
		Student s = stuMapper.selectStuByCode("stu-1011");  //一对多查询用的
		System.out.println(s);
	}
	@BeforeEach
	void setUp() throws Exception {
		sqlSession = MyBatisUtil.getSqlSession();
		stuMapper = sqlSession.getMapper(StudentMapper.class);
		courMapper = sqlSession.getMapper(CourMapper.class);
	}

	@AfterEach
	void tearDown() throws Exception {
		sqlSession.commit();
		sqlSession.close();
	}

	

}