Can't add and update values using Spring Boot connecting to PostgreSQL database

Question

I'm trying to update a 'Student' from PostgreSQL Database, but it only deletes the old value and creates a new id value for the new Student, with all the other fields empty.

Here is the class for "Student", from "Persistence" package, "Entity" subpackage:

@Entity

@Table(name = "student")

public class Student {

@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "student_id_seq")
@SequenceGenerator(name="student_id_seq", sequenceName = "student_id_seq", allocationSize=1)
@Column(name = "id", nullable = false)
private Integer id;

@Column
private String studentName;

@Column
private Integer studentGroup;

@Column
private String courseName;

@Column
private Integer studentGrades;


public Integer getId() {
    return id;
}

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

public String getStudentName() {
    return studentName;
}

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

public Integer getStudentGroup() {
    return studentGroup;
}

public void setStudentGroup(Integer group) {
    this.studentGroup = group;
}

public String getCourseName() { return courseName;}

public void setCourseName(String courseName) {this.courseName = courseName;}

public Integer getStudentGrades() {
    return studentGrades;
}

public void setStudentGrades(Integer grades) {
    this.studentGrades = grades;
}
}

This is how my interface for "Repository" subpackage (also from "Persistence" package) looks like :

public interface StudentRepository extends JpaRepository {}

In "StudentService" ("Business" package) I have the operations for create, update, delete and view all the students I have :

@Service
public class StudentService {

@Inject
StudentRepository studentRepository;

public List getAllStudentssWithCourses()
{
    return studentRepository.findAll();
}

public Student create(Student newStudent)
{
    return studentRepository.save(newStudent);
}

public void update(Student newStudent, Student oldStudent){
    if(oldStudent == null){
        System.out.println("ERROR! Student does not exist !!!");
    } else{
        newStudent.setId(oldStudent.getId());
        newStudent.setStudentName(newStudent.getStudentName());
        newStudent.setStudentGroup(newStudent.getStudentGroup());
        newStudent.setCourseName(newStudent.getCourseName());
        newStudent.setStudentGrades(newStudent.getStudentGrades());
        studentRepository.save(newStudent);
    }
}


public void delete(Student student){
    studentRepository.delete(student);
}
}

In "Controller" package, I have :

@Controller
public class StudentController {

@Inject
StudentService studentService;

@RequestMapping(value = "/student", method = RequestMethod.GET)
public ModelAndView getStudents()
{
    List studentList = studentService.getAllStudentssWithCourses();

    ModelAndView mav = new ModelAndView("student_view");
    mav.addObject("studentsWithCoursesList", studentList);
    mav.addObject("newStudent", new Student());
    return mav;

}


@RequestMapping(value = "/student", method = RequestMethod.POST)
public ModelAndView postStudent(@RequestParam(value = "action") String action,@ModelAttribute(value = "newStudent") Student newStudent)
{
    if(action.equals("Create Student"))
        studentService.create(newStudent);
    else if(action.equals("Update Student"))
        studentService.update(new Student(), newStudent);
    else
        studentService.delete(newStudent);
    return new ModelAndView("redirect:student");
}
}

My "student_view" in html looks like :

 

 Welcome, student user !
 
 
 
  student.ID
  student.NAME
  student.GROUP
  student.COURSE
  student.GRADES
 
 
 
 

  ID
  
  
  
  
  
 
 
 

 

 

 


  
  
    Student ID
    
  
  
    Student Name
    
  
  
    Student Group
    
  
  
    Course Name
    
  
  
    Student Grades

My main class :

@SpringBootApplication()

public class Assignment2 {
   public static void main(String[] args){
       SpringApplication.run(Assignment2.class, args);

   }
}

In my "application.properties", I have :

spring.jpa.database = POSTGRESQL
spring.jpa.show-sql = false
spring.jpa.hibernate.ddl-auto = validate
spring.jpa.properties.hibernate.jdbc.lob.non_contextual_creation = true


spring.datasource.driverClassName = org.postgresql.Driver
spring.datasource.url = jdbc:postgresql://localhost:5432/ps2
spring.datasource.username = postgres
spring.datasource.password = root

spring.thymeleaf.cache = false

spring.jpa.properties.hibernate.temp.use_jdbc_metadata_defaults = false
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQLDialect

server.port = 8090

My database in PostgreSQL :

CREATE TABLE public.student
(
    id integer NOT NULL,
    student_name character varying COLLATE pg_catalog."default",
    student_group integer,
    course_name character varying COLLATE pg_catalog."default",
    student_grades integer,
    CONSTRAINT "Student_pkey" PRIMARY KEY (id)
)
WITH (
    OIDS = FALSE
)
TABLESPACE pg_default;

ALTER TABLE public.student
OWNER to postgres;
-----
CREATE SEQUENCE public.student_id_seq;

ALTER SEQUENCE public.student_id_seq
    OWNER TO postgres;

Finally, in "pom.xml", I have :



4.0.0

com.example
demo1
0.0.1-SNAPSHOT
demo1
Demo project for Spring Boot


    org.springframework.boot
    spring-boot-starter-parent
    2.1.1.RELEASE




    UTF-8
    UTF-8
    1.8



    
        org.hibernate
        hibernate-entitymanager
        5.2.3.Final
    

    
        org.hibernate
        hibernate-core
        5.2.1.Final
    

    
        org.springframework.boot
        spring-boot-starter-data-jpa
    
    
        org.springframework.boot
        spring-boot-starter-thymeleaf
    

    
        org.springframework.boot
        spring-boot-starter-validation
    

    
        org.springframework.boot
        spring-boot-starter-web
    

    
        org.springframework.boot
        spring-boot-devtools
    

    
        org.springframework.boot
        spring-boot-starter-test
        test
    


    
        org.postgresql
        postgresql
        runtime
    


    
        javax.inject
        javax.inject
        1
    

    
    
        postgresql
        postgresql
        9.1-901-1.jdbc4
    





    
        
            org.springframework.boot
            spring-boot-maven-plugin

Lesiak · Accepted Answer

The GenerationType.IDENTITY relies on a database auto-increment column to generate the id.

Your Student.id column in the dB is clearly not auto-increment.

I believe that standard syntax for auto-increment is available since Postgres10

PostgreSQL Autoincrement

See also https://thoughts-on-java.org/jpa-generate-primary-keys/ for an intro on different generation strategies. And the following question How to choose the id generation strategy when using JPA and Hibernate

Summing up SEQUENCE is the best available option, IDENTITY is only a good choice when you cannot use SEQUENCE because it disables JDBC batch updates.

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