摘要：數(shù)據(jù)庫關(guān)系模型中有一對一一對多關(guān)系首先建立如下表繼續(xù)用最經(jīng)典的學(xué)生管理系統(tǒng)建表模型圖如圖所示學(xué)生表為中心學(xué)生證表和其為一對一關(guān)系學(xué)生表和課程表為一對多一對一關(guān)系因?yàn)樯蠄D中學(xué)生和學(xué)生關(guān)系為一對一關(guān)系由于是數(shù)據(jù)庫的一對一關(guān)系那么對應(yīng)的中也應(yīng)該是

數(shù)據(jù)庫關(guān)系模型中有一對一,一對多,關(guān)系,
首先建立如下表 繼續(xù)用最經(jīng)典的學(xué)生管理系統(tǒng)

模型圖如圖所示

學(xué)生表為中心
學(xué)生證表和其為一對一關(guān)系
學(xué)生表和課程表為一對多

因?yàn)樯蠄D中,學(xué)生和學(xué)生關(guān)系為一對一關(guān)系.
由于是數(shù)據(jù)庫的一對一關(guān)系,那么對應(yīng)的bean中,也應(yīng)該是一對一關(guān)系
舉栗子的表為學(xué)生表和學(xué)生證表
其中學(xué)生證表的中的學(xué)生編號(hào)的外鍵為學(xué)生表的主鍵
那么在學(xué)生表的POJO對象中,應(yīng)該有學(xué)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(dāng)查詢到studentCard的時(shí)候,將會(huì)調(diào)用com.ming.MyBatis.RoleMapper.findStudentSelfCardByStudentId sql語句的執(zhí)行

對于數(shù)據(jù)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(shí)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(jié)束時(shí)間

%>

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

        <%
    }
%>

這個(gè)和上方同理,跳過

根據(jù)學(xué)生信息去關(guān)聯(lián)男性或者女性的健康指標(biāo)

兩個(gè)類只需要繼承同一個(gè)類,使用case語句即可.
跳過

在使用級(jí)聯(lián)的時(shí)候,會(huì)造成多條sql語句的執(zhí)行,此時(shí),使用延遲加載

一開始不使用sql語句,只有當(dāng)使用了sql才去發(fā)送數(shù)據(jù)

在setting這里設(shè)置,可以降低sql語句的執(zhí)行問題

一般情況下是層級(jí)加載,取消層級(jí)加載,使用aggressiveLazyLoading值設(shè)置為false即可

寫原生sql 這個(gè)很簡單,跳過