I have tow Entities Joined (University and Student) To post new student I send a json file to spring like this :
{"cne":132,
"universitymap":{existing university }}
my problem : I don't want to post existing university with the student
i need to post new student with new university in the seem time!!
#Entity
public class University {
#Id
#GeneratedValue( strategy= GenerationType.AUTO )
#Column(name = "id_university")
private int id_university;
#Column(name = "nom")
private String nom;
#OneToMany(mappedBy = "univeersitymap",cascade=CascadeType.ALL)
private List<Student> student;
#getters & setters
-------------------------------
#Entity
public class Student {
#Id
#GeneratedValue( strategy= GenerationType.AUTO )
#Column(name = "id_student")
private int id_student;
#Column(name = "cne")
private Date cne;
#ManyToOne(fetch=FetchType.LAZY)
#JoinColumn(name="university_id")
private University universitymap;
#getters & setters
Related
I need to fetch names of all students who have enrolled for the courses.
Url:-/students/{course1}/{course2}
Eg /students/java/oracle
How to write controller, service and repository in rest api.
Entity:-
Student
Integer Id,String name and list coursenames
What about?
#Controller
#RequestMapping("/students")
public class StudentController {
#Autowired
private StudentService studentService;
// /students/java,oracle
#GetMapping(value="/{courses}")
#ResponseBody
public String getStudents(#PathVariable String[] courses) {
return studentService.getStudents(courses);
}
}
Student
#Entity
#Table(name = "student")
public class StudentDao {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#Column(name = "name")
private String name;
#OneToMany(fetch = FetchType.EAGER)
#Fetch(value = FetchMode.SUBSELECT)
#JoinColumn(name = "id", referencedColumnName = "id")
private List<CourseDao> course;
}
Course
#Entity
#Table(name = "course")
public class CourseDao {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#Column(name = "name")
private String name;
}
In my opinion it is bad rest design. I'll create POST endpoint with body, which contains array with course Id's and find students by course id's.
If the parameters are optional or an array you shouldn't use a path variable but use a request parameter.
I have two simple classes Student and Course. I am trying to set up many to many relationship between these classes. I want to use additional table whose PRIMARY KEY is the combination of the primary keys of student and course tables (student_id and course_id).
The student class:
#Entity
#Table(name = "student")
#Getter
#Setter
#AllArgsConstructor
#NoArgsConstructor
public class Student {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
#Column(name = "name")
private String name;
#Column(name = "surname")
private String surname;
#OneToMany(mappedBy = "student")
private Set<CourseStudent> courses;
}
The course class:
#Entity
#Table(name = "course")
public class Course {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String courseName;
#OneToMany(mappedBy = "course")
Set<CourseStudent> students;
}
The entity that stores the relationship between course and the student:
#Entity
#NoArgsConstructor
#Data
public class CourseStudent {
#EmbeddedId
CourseStudentKey id;
#ManyToOne
#MapsId("studentId")
#JoinColumn(name = "student_id")
Student student;
#ManyToOne
#MapsId("courseId")
#JoinColumn(name = "course_id")
Course course;
public CourseStudent(Student student, Course course) {
this.student = student;
this.course = course;
this.rating = 0;
}
int rating;
}
Attention: Since I want to have additional features in this entity (for example, storing the rating of the students for courses), I don't want to use #JoinTable idea that we implement in the Student class.
Since I have multiple attributes in the primary key of CourseStudent entity, I used the following class
#Embeddable
#Data
public class CourseStudentKey implements Serializable {
#Column(name = "student_id")
Long studentId;
#Column(name = "course_id")
Long courseId;
}
I have the following POST request to insert the student into a course:
#PostMapping("/insert/students/{studentId}/courses/{courseId}")
public CourseStudent insertStudentIntoCourse(#PathVariable(value = "studentId") Long studentId,
#PathVariable(value = "courseId") Long courseId) {
if (!studentRepository.existsById(studentId)) {
throw new ResourceNotFoundException("Student id " + studentId + " not found");
}
if (!courseRepository.existsById(courseId)) {
throw new ResourceNotFoundException("Course id " + courseId + " not found");
}
CourseStudent courseStudent = new CourseStudent(
studentRepository.findById(studentId).get(),
courseRepository.findById(courseId).get()
);
return courseStudentRepository.save(courseStudent);
}
I have manually added Student and the Course into my local database and send this request by using Postman.
http://localhost:8080/insert/students/1/courses/1
However, I get the following error:
{
"timestamp": "2022-08-04T12:33:18.547+00:00",
"status": 500,
"error": "Internal Server Error",
"path": "/insert/students/1/courses/1"
}
In the console, I get NullPointerException. What is the thing I am doing wrong here?
I have some trouble with joining tables using Spring Boot JPA
I need to do this kind of joining:
**book2user — book to user
id INT NOT NULL AUTO_INCREMENT
time DATETIME NOT NULL
type_id INT NOT NULL
book_id INT NOT NULL
user_id INT NOT NULL**
Here are my Entity classes:
#Entity
#Table(name = "user")
public class User {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
private String hash;
private Date reg_time;
private Integer balance = 0;
private String name;
// getters and setters
public class Book {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#ManyToOne
#JoinColumn(name = "author_id", referencedColumnName = "id")
private Author author;
#ManyToOne
#JoinColumn(name = "genre_id", referencedColumnName = "id")
private Genre genre;
private String title;
private String slug;
private String description;
private String priceOld;
private String price;
private String image;
private boolean is_bestseller;
private Date pub_date;
// getters and setters
In order to do this kind of joining I should create another entity class ??
Something like this should work:
#Entity
#Table("book2user")
public class Book2User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
private LocalDateTime time;
private Integer typeId;
#OneToOne
private Book book;
#OneToOne
#JoinColumn(name = "user_id") //optional, if the name of the table and field matches.
private User user;
}
I have created two Entities namely Teacher and Detail, the code snippet is shown below
Teacher.java
#Entity
#Table(name = "teacher")
public class Teacher implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private long id;
#Column(name = "name")
private String name;
#Column(name = "age")
private int age;
#OneToOne(mappedBy = "teacher", cascade = CascadeType.ALL)
private Detail detail;
public Teacher() {
}
public Teacher(String name, int age) {
this.name = name;
this.age = age;
}
//getter and setter
}
Detail.java
#Entity
#Table(name = "detail")
public class Detail implements Serializable {
#Id
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "id")
private Teacher teacher;
#Column(name = "subjects")
private String subjects;
public Detail() {
}
public Detail(String subjects) {
this.subjects = subjects;
}
//getter and setter
}
I am trying to achieve one to one mapping with the shared primary key concept
but when i execute the controller, only Teacher table is updating with the value
try {
Teacher teacher=new Teacher("xyz",23);
Detail detail=new Detail("Java,c,c++");
teacher.setDetail(detail);
session.beginTransaction();
session.save(teacher);
session.getTransaction().commit();
model.addAttribute("added", "data inserted");
session.close();
}
After executing only Teacher table is updated with the specified values.Detail table is still showing empty
It does not work exactly like that. You still need the id field in your Detail, so add:
#Id
private long id;
to your Deatail class.
And - as comment suggests - replace the #Id annotation in field Teacher to #MapsId. This way the id of Teacher is mapped to the id of Detail BUT ONLY if you also set the teacher to the detail - you always need to set both sides of relationship - like:
teacher.setDetail(detail);
detail.setTeacher(teacher);
I have 'Course' and 'Student' entities. They have many-to-many relation. So, i have COURSE_STUDENT(contains 'student_id' and 'course_id' columns) table. I want to register students to courses with a button.(For example; a student lists courses and click Register button to register a specific course).
When i want to create new courses, i use courseRepository and courseMapper which comes from JHipster by default.
But i don't have repository and mapper files for COURSE_STUDENT. Because it is not actually a main entity. It is created for many-to-many relation.
How can i register students to courses?
Git repo:https://github.com/canberkizgi/monolithic-mucs
My course entity:
#Entity
#Table(name = "course")
#Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public class Course implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#NotNull
#Column(name = "title", nullable = false)
private String title;
#Column(name = "description")
private String description;
#ManyToOne
private Instructor instructor;
#ManyToMany(fetch = FetchType.EAGER)
#Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
#JoinTable(name = "course_student",
joinColumns = #JoinColumn(name="courses_id", referencedColumnName="id"),
inverseJoinColumns = #JoinColumn(name="students_id", referencedColumnName="id"))
private Set<Student> students = new HashSet<>();
Student entity:
#Entity
#Table(name = "student")
#Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public class Student implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#OneToOne
#JoinColumn(unique = true)
private User user;
#ManyToMany(fetch = FetchType.EAGER,mappedBy = "students")
#JsonIgnore
#Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
private Set<Course> courses = new HashSet<>();
For example; Createcourse function with Mapper and Repository
#PostMapping("/courses")
#Timed
public ResponseEntity<CourseDTO> createCourse(#Valid #RequestBody CourseDTO courseDTO) throws URISyntaxException {
log.debug("REST request to save Course : {}", courseDTO);
if (courseDTO.getId() != null) {
return ResponseEntity.badRequest().headers(HeaderUtil.createFailureAlert(ENTITY_NAME, "idexists", "A new course cannot already have an ID")).body(null);
}
Course course = courseMapper.toEntity(courseDTO);
course = courseRepository.save(course);
CourseDTO result = courseMapper.toDto(course);
return ResponseEntity.created(new URI("/api/courses/" + result.getId()))
.headers(HeaderUtil.createEntityCreationAlert(ENTITY_NAME, result.getId().toString()))
.body(result);
}
The relationship is owned by the course entity. Thats because on the student side the #ManyToMany annotation has a mappedBy attribute. This means, that the database will reflect the set in the course. You need to add students to that set to save the relationship. That change needs to be done within a transaction.
That being said it would probably be best to follow DDD here. I would create a registerTo method in the student class that would take the course as a parameter. I would then call this.courses.add(course) and course.getStudents().add(this) in that method.