摘要：數據庫關系模型中有一對一一對多關系首先建立如下表繼續用最經典的學生管理系統建表模型圖如圖所示學生表為中心學生證表和其為一對一關系學生表和課程表為一對多一對一關系因為上圖中學生和學生關系為一對一關系由于是數據庫的一對一關系那么對應的中也應該是

數據庫關系模型中有一對一,一對多,關系,
首先建立如下表 繼續用最經典的學生管理系統

模型圖如圖所示

學生表為中心
學生證表和其為一對一關系
學生表和課程表為一對多

因為上圖中,學生和學生關系為一對一關系.
由于是數據庫的一對一關系,那么對應的bean中,也應該是一對一關系
舉栗子的表為學生表和學生證表
其中學生證表的中的學生編號的外鍵為學生表的主鍵
那么在學生表的POJO對象中,應該有學生證表的POJO的映射.即

package com.ming.MyBatis.POJO;

/**
 * @author ming
 */
public class Student {
    private int uid;
    private String studentName;
    private String gender;
    private String studentIdNumber;
    private String remarks;
    private StudentCard studentCard;

    public void setStudentCard(StudentCard studentCard) {
        this.studentCard = studentCard;
    }

    public StudentCard getStudentCard() {
        return studentCard;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public void setStudentIdNumber(String studentIdNumber) {
        this.studentIdNumber = studentIdNumber;
    }

    public void setRemarks(String remarks) {
        this.remarks = remarks;
    }

    public int getUid() {
        return uid;
    }

    public String getStudentName() {
        return studentName;
    }

    public String getGender() {
        return gender;
    }

    public String getStudentIdNumber() {
        return studentIdNumber;
    }

    public String getRemarks() {
        return remarks;
    }
}

對于card的POJO如下所示

package com.ming.MyBatis.POJO;


import java.util.Date;

/**
 * @author ming
 */
public class StudentCard {
    private int uid;
    private String studentNumber;
    private String birthplace;
    private Date dateOfIssue;
    private Date endDate;
    private String remarks;

    public void setUid(int uid) {
        this.uid = uid;
    }

    public void setStudentNumber(String studentNumber) {
        this.studentNumber = studentNumber;
    }

    public void setBirthplace(String birthplace) {
        this.birthplace = birthplace;
    }

    public void setDateOfIssue(Date dateOfIssue) {
        this.dateOfIssue = dateOfIssue;
    }

    public void setEndDate(Date endDate) {
        this.endDate = endDate;
    }

    public void setRemarks(String remarks) {
        this.remarks = remarks;
    }

    public int getUid() {
        return uid;
    }

    public String getStudentNumber() {
        return studentNumber;
    }

    public String getBirthplace() {
        return birthplace;
    }

    public Date getDateOfIssue() {
        return dateOfIssue;
    }

    public Date getEndDate() {
        return endDate;
    }

    public String getRemarks() {
        return remarks;
    }
}

先增加StudentCard的配置

        
        
        
        
        
        
    

    
        SELECT student_card.uid, student_card.student_number, student_card.remarks,
        student_card.end_date, student_card.date_of_issue, student_card.birthplace
        FROM student_card WHERE student_card.uid = #{studentId};
    

再增加Student的映射

    
        
        
        
        
        
        
        
    
    
    
        SELECT student.uid, student.gender, student.remarks, student.student_id_number,
        student.student_name
        FROM student
        WHERE student.uid = 1;
    

可以看到當查詢到studentCard的時候,將會調用com.ming.MyBatis.RoleMapper.findStudentSelfCardByStudentId sql語句的執行

對于數據展示層來說

<%@ page import="org.apache.ibatis.session.SqlSession" %>
<%@ page import="com.ming.Util.SqlSessionFactoryUtil" %>
<%@ page import="com.ming.MyBatis.RoleMapper" %>
<%@ page import="java.util.List" %>
<%@ page import="java.util.Iterator" %>
<%@ page import="com.ming.MyBatis.POJO.Student" %>


Hello World!

<%
    long startTime = System.currentTimeMillis(); //獲取開始時間
    SqlSession sqlSession = null;
    List students = null;
    for(int i = 0; i < 10; i++) {
        try {
            sqlSession = SqlSessionFactoryUtil.openSqlSesion();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            students = roleMapper.getStudent(1);
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }
    long endTime = System.currentTimeMillis(); //獲取結束時間

%>

<%
    Iterator iterator = students.iterator();
    while(iterator.hasNext()){
        %>
            <%=((Student)iterator.next()).getStudentCard().getEndDate()%>

        <%
    }
%>

這個和上方同理,跳過

根據學生信息去關聯男性或者女性的健康指標

兩個類只需要繼承同一個類,使用case語句即可.
跳過

在使用級聯的時候,會造成多條sql語句的執行,此時,使用延遲加載

一開始不使用sql語句,只有當使用了sql才去發送數據

在setting這里設置,可以降低sql語句的執行問題

一般情況下是層級加載,取消層級加載,使用aggressiveLazyLoading值設置為false即可

寫原生sql 這個很簡單,跳過