@GeneratedValue annotation is not working on mapping table

Question

I have a many to many relationship like below.

@Entity
@Table(name = "employees")
public class Employee {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Column(name = "EMP_ID")
  private int id;
  
  private String firstName;
  private String lastName;

  @JoinTable(name = "employee_project_mapping", joinColumns = @JoinColumn(name = "EMPLOYEE_ID", referencedColumnName = "EMP_ID"), inverseJoinColumns = @JoinColumn(name = "PROJECT_ID", referencedColumnName = "PJT_ID"))
  @JsonManagedReference
  @ManyToMany(cascade = CascadeType.ALL)
  Set<Project> projects = new HashSet<Project>();
  .....
  .....
}



@Entity
@Table(name = "projects")
public class Project {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Column(name = "PJT_ID")
  private int projectId;

  private String projectName;

  private int teamSize;

  @ManyToMany(mappedBy = "projects")
  @JsonBackReference
  private Set<Employee> emps = new HashSet<Employee>();
  .....
  .....
}

@Entity
@Table(name = "employee_project_mapping")
public class EmployeeProjectMapping {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Column(name = "EMP_PJT_ID")
  private Integer empPjtId;

  @Column(name = "PROJECT_ID")
  private Integer projectId;

  @Column(name = "EMPLOYEE_ID")
  private Integer emploeeId;

  .....
  .....
}

But when I am trying to insert an employee object with set of projects, it is failing to create auto generated id for the column EMP_PJT_ID (this is an id to the mapping table record). Can't I add an auto generated id for mapping table using jpa?

Error trace

Hibernate: insert into employees (emp_id, first_name, last_name) values (null, ?, ?)
Hibernate: insert into employee_project_mapping (employee_id, project_id) values (?, ?)
2021-04-22 23:34:25.973 ERROR 24126 --- [nio-8080-exec-9] o.h.engine.jdbc.spi.SqlExceptionHelper   : NULL not allowed for column "EMP_PJT_ID"; SQL statement:
insert into employee_project_mapping (employee_id, project_id) values (?, ?) [23502-200]
2021-04-22 23:34:25.975 ERROR 24126 --- [nio-8080-exec-9] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement] with root cause

org.h2.jdbc.JdbcSQLIntegrityConstraintViolationException: NULL not allowed for column "EMP_PJT_ID"; SQL statement:
insert into employee_project_mapping (employee_id, project_id) values (?, ?) [23502-200]

GeneratedValue with a type IDENTITY means something in the database will be setting the value for you, which is why it is left out of the insert. You don't have that setup in your database for the EMP_PJT_ID column, which is why you get the error. You'll need to setup that column to use identity as it must be for the other IDENTITY columns for this to work — Chris
– Chris, Commented Apr 22, 2021 at 18:54

Davide D'Alto · Accepted Answer · 2021-04-22 18:36:23Z

The mapping of a many-to-many should be:

@Entity
@Table(name = "employees")
public class Employee {
...

  @OneToMany(mappedBy = "employee", cascade = CascadeType.ALL, orphanRemoval = true)
  Set<EmployeeProjectMapping> projects = new HashSet<EmployeeProjectMapping>();
...

    // Utility method to update both sides of the association
    public void addProject(Project project) {
        EmployeeProjectMapping empProject = new PersEmployeeProjectMappingonAddress( this, project );
        projects.add( empProject );
        project.getEmployees().add( empProject );
    }
}


@Entity
@Table(name = "projects")
public class Project {
...
   @OneToMany(mappedBy = "project", cascade = CascadeType.ALL, orphanRemoval = true)
   private Set<EmployeeProjectMapping> emps = new HashSet<Employee>();
...
}

@Entity
@Table(name = "employee_project_mapping")
public class EmployeeProjectMapping {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Column(name = "EMP_PJT_ID")
  private Integer empPjtId;

  @Id
  @ManyToOne
  @JoinColumn(name = "PROJECT_ID")
  private Project project;

  @Id
  @ManyToOne
  @JoinColumn(name = "EMPLOYEE_ID")
  private Employee employee;

  .....
  .....
}

Make sure to check the example on the Hibernate ORM documentation for all the details.

Collectives™ on Stack Overflow

@GeneratedValue annotation is not working on mapping table

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related