问CRUD手术未能正确显示师生及其科目
EN

Stack Overflow用户

提问于 2022-04-10 05:51:16

回答 1查看 90关注 0票数 0

当我做时，GET请求显示与学生以及学生所拥有的科目有关的教师数据，学生数据丢失，主题数据被添加到一个学生中，而不是将学生和他们的科目分开。

这里是邮递员的样子：

这里的是我希望GET请求输出看起来像：

{
    "id": 1,
    "university_id": 1,
    "name": "FSHMN",
    "Enrolled Students:": [
        {
            "id": "5",
            "username": "Johnny",
            "password": "d123",
            "fullname": "Depp",
            "email": "Johnny@gmail.com",
            "subjects": [
                {
                    "id": 1,
                    "name": "Programim 1"
                },
                {
                    "id": 2,
                    "name": "Programim 2"
                },
                
                 {
                    "id": 3,
                    "name": "Calculus"
                },
                
                {
                    "id": 4,
                    "name": "Discrete mathematics"
                },
             ]
                
            "id": "4",
            "username": "Student2",
            "password": "d123",
            "fullname": "studentfull",
            "email": "student@gmail.com", 
            "subjects": [
          
                {
                    "id": 1,
                    "name": "Programim 1"
                },
                {
                    "id": 2,
                    "name": "Programim 2"
                },
                {
                    "id": 3,
                    "name": "Calculus"
                },
                {
                    "id": 4,
                    "name": "Discrete mathematics"
                }
            ]
        }
    ]
}

我希望被录取的学生和他们的科目分开，所以在这里我需要知道哪些概念才能使这个工作正常进行。

这里是我的代码：

GET请求正在调用的方法：

 public Faculty  getFacultyStudent(int id) throws Exception {
        Connection connection = null;

        Faculty faculty = new Faculty();
        Student student = new Student();
        student.setSubjectList(new ArrayList<>());
        faculty.setStudentList(new ArrayList<>());

        try {
            connection = new MysqlDbConnectionService().getConnection();


            String select = "SELECT f.fid,\n" +
                    "      f.fname,\n" +
                    "      f.university_id,\n" +
                    "       s.user_id,\n" +
                    "       s.username,\n" +
                    "       s.password,\n" +
                    "       s.fullname,\n" +
                    "       s.email,\n" +
                    "       subj.id,\n" +
                    "       subj.name\n" +
                    "FROM faculty f\n" +
                    "         INNER JOIN student_faculty sf ON sf.faculty_id=f.fid \n" +
                    "         INNER JOIN student s ON sf.student_id=s.user_id\n" +
                    "         INNER JOIN faculty_subject fs ON f.fid = fs.faculty_id\n" +
                    "         INNER JOIN subject subj ON fs.subject_id = subj.id\n" +
                    "WHERE fid = ?";



            PreparedStatement ps = connection.prepareStatement(select);

            ps.setInt(1, id);

            ResultSet rs = ps.executeQuery();


            while (rs.next()) {
                if(faculty.getFid()==0) {
                   faculty.setFid(rs.getInt("fid"));
                    faculty.setUniversityid(rs.getInt("university_id"));
                   faculty.setFname(rs.getString("fname"));


                }

                student.setId(rs.getString("user_id"));
                student.setUsername(rs.getString("username"));
                student.setPassword(rs.getString("password"));
                student.setFullName(rs.getString("fullname"));
                student.setEmail(rs.getString("email"));

                Subject subject=new Subject();
                subject.setId(rs.getInt("id"));
                subject.setName(rs.getString("name"));
                student.getSubjectList().add(subject);


            }

        } catch (Exception e) {
            System.out.println(e + " Retrieve not successful");

        }

        faculty.getStudentList().add(student);

        return faculty;


    }

学院班级：

package com.common.db.domain;
import com.google.gson.annotations.SerializedName;

import java.util.Collections;
import java.util.List;


public class Faculty {


    @SerializedName("id")
    private int fid;

    @SerializedName("university_id")
    private int university_id;

    @SerializedName("name")
    private String fname;

    @SerializedName("Enrolled Students:")
    private List<Object> studentList;


    public Faculty() {
        this.fid = fid;
        this.university_id=university_id;
    }

    public  void setFid(int fid)
    {

        this.fid = fid;
    }

    public int getFid()
    {

        return fid;
    }

    public  void setUniversityid(int university_id)
    {

        this.university_id=university_id;
    }

    public int getUniversityid()
    {

        return university_id;
    }

    public void setFname(String fname)
    {
        this.fname = fname;
    }

    public String getFname()
    {
        return fname;
    }

    public void setStudentList(List<Object> studentList) {
        this.studentList = studentList;
    }

    public List<Object> getStudentList()
    {
        return studentList;
    }

}

学生班：

package com.common.db.domain;


import com.google.gson.annotations.SerializedName;

import java.util.List;

public class Student {


    @SerializedName("id")
    private String id;

    @SerializedName("username")
    private String username;

    @SerializedName("password")
    private String password;

    @SerializedName("fullname")
    private String fullName;

    @SerializedName("email")
    private String email;

    @SerializedName("subjects")
    private List<Subject> subjectList;


    public Student() {

    }


    public Student(String id, String username, String password, String fullName, String email) {
        super();
        this.id = id;
        this.username = username;
        this.password = password;
        this.fullName = fullName;
        this.email = email;
    }


    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getFullName() {
        return fullName;
    }

    public void setFullName(String fullName) {
        this.fullName = fullName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public List<Subject> getSubjectList() {
        return subjectList;
    }

    public void setSubjectList(List<Subject> subjectList) {
        this.subjectList = subjectList;
    }
}

主题类：

package com.common.db.domain;
import com.google.gson.annotations.SerializedName;
public class Subject {




    @SerializedName("id")
    private int id;

    @SerializedName("name")
    private String name;


    public Subject() {
        this.id = id;
        this.name=name;
    }

    public  void setId(int id)
    {
      this.id=id;
    }

    public int getId()
    {
        return id;
    }

    public void setName(String name)
    {
        this.name=name;
    }

    public String getName()
    {
        return name;
    }



}

ER图：

我需要在我的方法中做什么改变或补充，才能把学生和他们的相应科目分开。

java

mysql

回答 1

Stack Overflow用户

回答已采纳

发布于 2022-04-12 14:53:08

        Map<String, Student> studentMap = new HashMap<>();
        while (rs.next()) {
            if(faculty.getFid()==0) {
               faculty.setFid(rs.getInt("fid"));
                faculty.setUniversityid(rs.getInt("university_id"));
               faculty.setFname(rs.getString("fname"));


            }
            String userID = rs.getString("user_id");

            if(!studentMap.containsKey(userID)){
                student = new Student();
                student.setId(rs.getString("user_id"));
                student.setUsername(rs.getString("username"));
                student.setPassword(rs.getString("password"));
                student.setFullName(rs.getString("fullname"));
                student.setEmail(rs.getString("email"));
                student.setSubjectList(new ArrayList<>());
                studentMap.put(userID, student);
            }else{
                student = studentMap.get(userID);

            }
            

            Subject subject=new Subject();
            subject.setId(rs.getInt("id"));
            subject.setName(rs.getString("name"));
            student.getSubjectList().add(subject);


        }
        faculty.getStudentList().addAll(studentMap.values());