Postgres Hibernate Primary Key generation Issue

Question

I am trying to insert a record in Employee table with Hibernate ORM but keep getting an error as :

org.hibernate.AssertionFailure: null id in 
com.example.helloworld.entities.Employee entry (don't flush the Session 
after an exception occurs)

If I pass ID value then it works fine but although I have used @GeneratedValue(strategy = GenerationType.IDENTITY) it does not generate 'id' automatically. Any help is appreciated! Details on DB schema and entity code is as given below.

DB Engine: Postgres

ORM : Hibernate

I have following two tables :

Table Name Employee:

---

Column Name |  Type      |  Length    |  Not Null  | Default
name        | Varchar    |  64        |  true      | NULL 
id          |  int8      |  19        |  true      |nextval(Employee_id::regclass)
company_id  |  int8     |19           |  true      | NULL

Table #Company

Column Name |  Type      |  Length    |  Not Null  | Default
Cname       | Varchar    |  64        |  true      | NULL 
id          |  int8      |  19        |  true      | nextval(Company_id::regclass) 

 area       |  varchar    |64          |  true      | NULL 

Entity Java Classes for above tables :

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

    public Employee() {super();}

    @Id
    @Column(name = "id", columnDefinition = "serial")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @NotNull
    private long id;

    @NotNull
    @Column(name = "company_id")
    private long company_id;

    @NotNull
    @Column(name = "name")
    private String name;

    @ManyToOne
    private Company company;

   /**
   setters and getters
   **/
}

@Entity
@Table(name = "Company")
public class Company {

    public Company() {super();}

    @Id
    @Column(name = "id", columnDefinition = "serial")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @NotNull
    private long id;

    @NotNull
    @Column(name = "area")
    private String area;

    @NotNull
    @Column(name = "cname")
    private String cname;

    @OneToMany(cascade=CascadeType.ALL)
    @JoinColumn(name="company_id")
    private Set<Employee> employees;

   /**
   setters and getters
   **/
}

Answer 1

This is what worked for me :

@Id
@Column(name = "id", columnDefinition = "serial")
@GeneratedValue(strategy = GenerationType.IDENTITY, generator="seq_name_generated_in_db")
@SequenceGenerator(name="seq_name_generated_in_db", sequenceName="seq_name_generated_in_db", initialValue = 1 , allocationSize=1)