Spring-Hibernate insertion Error with Column 'unit_id' cannot be null Exception - spring

Question

I am developing a small Spring and hibernate base application in java, and my appication has a one to many relationship with Employee and Unit, Employee has a one unit, Unit has a many Employee.
in this small application genarate error like this `
I was hard code data to Unit schema table, i populate unit combobox filled in jsp its works, but inside the #controller unit has a null data.
com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException:
Column 'unit_id' cannot be null
if allow to null value to unit_id other data inserted with out insert unit_id
here my Entity class
#Entity
#Table(name = "employee")
public class Employee implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Integer id;
#Column(name = "epf")
private int epf;
#Column(name = "fname")
private String fname;
#Column(name = "lname")
private String lname;
#Column(name = "email")
private String email;
#JoinColumn(name = "unit_id", referencedColumnName = "id")
#ManyToOne//(optional = false)
private Unit unit;
#Entity
#Table(name = "unit")
public class Unit implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Integer id;
#Column(name = "name")
My controller Class
#Autowired
private EmployeeService employeeService;
private DesignationService designationService;
#RequestMapping({"/index", "/"})
public String setupForm(Map<String, Object> map){
Employee student = new Employee();
map.put("employee", student);
map.put("employeeList", employeeService.getAllEmployee());
map.put("unitList", employeeService.getAllUnitList());
return "employee";
}
#RequestMapping(value="/employee.do", method=RequestMethod.POST)
public ModelAndView doActions(#ModelAttribute Employee emp, BindingResult result, #RequestParam String action, Map<String, Object> map){
ModelAndView modelAndView = new ModelAndView("employee");
Employee employeetResult = new Employee();
switch(action.toLowerCase()){ //only in Java7 can put String in switch
case "add":
employeeService.addEmployee(emp);
employeetResult = emp;
break;
case "edit":
employeeService.updateEmployee(emp);
employeetResult = emp;
break;
case "delete":
employeeService.deleteEmployee(emp.getId());
employeetResult = new Employee();
break;
case "search":
Employee searchedStudent = employeeService.getEmployee(emp.getId());
employeetResult = searchedStudent!=null ? searchedStudent : new Employee();
break;
}
map.put("employee", employeetResult);
map.put("employeeList", employeeService.getAllEmployee());
return modelAndView;
}
My JSP
<form:form action="employee.do" method="POST" commandName="employee">
<table width="341" border="0">
<tr>
<td width="154"> </td>
<td width="21"> </td>
<td width="152"> </td>
</tr>
<tr>
<td><spring:message code="employee.id"/></td>
<td> </td>
<td><form:input path="epf" /></td>
</tr>
<tr>
<td><spring:message code="employee.epf"/></td>
<td> </td>
<td><form:input path="epf" /></td>
</tr>
<tr>
<td><spring:message code="employee.fname"/></td>
<td> </td>
<td><form:input path="fname"/></td>
</tr>
<tr>
<td><spring:message code="employee.lname"/></td>
<td> </td>
<td><form:input path="lname" /></td>
</tr>
<tr>
<td><spring:message code="employee.email"/></td>
<td> </td>
<td><form:input path="email" /></td>
</tr>
<tr>
<td><spring:message code="employee.unit"/></td>
<td> </td>
<!-- Unit Combo filling --><td>
<form:select path="unit" multiple="false" size="1">
<form:options items="${unitList}" itemValue="id" itemLabel="name"/>
</form:select>
<!-- Unit Combo filling end --></td>
</tr>
<tr>
<td> </td>
<td> </td>
<td> </td>
</tr>
<tr>
<td colspan="2">
<input type="submit" name="action" value="Add" />
<input type="submit" name="action" value="Edit" />
<input type="submit" name="action" value="Delete" />
<input type="submit" name="action" value="Search" />
</td>
</tr>
</table>
</form:form>
My DAO Class
> #Repository public class EmployeeDaoImp implements EmployeeDao {
>
> #Autowired private SessionFactory sessionfactory;
> public void addEmployee(Employee emp) { sessionfactory.getCurrentSession().save(emp);
>
> }
>
> public void updateEmployee(Employee emp) {
> sessionfactory.getCurrentSession().update(emp);
>
> }
>
> public void deleteEmployee(int id) {
> sessionfactory.getCurrentSession().delete(getEmployee(id)); }
>
> Employee public Employee getEmployee(int empId) {
> return (Employee) sessionfactory.getCurrentSession().get(Employee.class,empId); }
>
> public List getAllEmployee() {
> return sessionfactory.getCurrentSession().createQuery("from Employee").list(); }

Answer 1

The id is primary key in the DB. You are save an object without giving it's value. So either make it auto increment in table or generate it's value using hibernate.