Sping MVC and hibernate: undeclared variable in jsp become null when saved - spring

Question

I just created my simple web application using Spring frameworks and hibernate. But I face the crucial problem when there is a transaction with my database.
When I tried to update my object, undeclared variables become null when saved to the database.
I will explain it with an example.
Model.java:
public class Model implements Serializable {
private int id;
private String firstName;
private String lastName;
private String description;
//setter getter
}
ModelDaoImpl.java:
#Repository("modelDao")
public class ModelDaoImpl implements ModelDao {
#Autowired
SessionFactory sessionFactory;
public Model create (Model model) throws Exception {
this.sessionFactory.getCurrentSession().save(model);
return model;
}
public Model update (Model model) throws Exception {
this.sessionFactory.getCurrentSession().update(model);
return model;
}
public Model get (Serializable id) throws Exception {
return (Model) this.sessionFactory.getCurrentSession().get(Model.class, id);
}
}
ModelServiceImpl.java:
#Service("modelService")
public class ModelServiceImpl implements ModelService {
#Autowired
modelDao modelDao;
#Transactional
public Model create (Model model) throws Exception {
return modelDao.create(model);
}
#Transactional
public Model update (Model model) throws Exception {
return modelDao.udpdate(model);
}
#Transactional
public Model get (Serializable id) throws Exception {
return modelDao.get(id);
}
}
ModelController.java:
#Controller
public class ModelController {
#Autowired
ModelService modelService
#RequestMapping(value="/editModel", method.RequestMethod.GET)
public String formCreator(ModelMap model, HttpServletRequest request) {
Integer id = new Integer(request.getParameter("id"));
Model modelData = new Model();
if (id != null) {
modelData = modelService.get(id);
}
model.addAttribute("modelData", modelData);
return "editModel"
}
#RequestMapping(value="/saveModel", method.RequestMethod.POST)
public String saveData(#ModelAttribute("modelData") Model modelData) {
if (modelData.getId() == null) {
modelService.create(modelData);
} else {
modelService.update(modelData);
}
return "redirect:/modelList";
}
//SKIP FOR GET MODEL LIST AND GET MODEL DETAIL
}
editModel.jsp:
<form:form action="${pageContext.request.contextPath}/saveModel" method="POST" modelAttribute="modelData">
<table>
<form:hidden path="id"/>
<tr>
<td>First Name:</td>
<td><form:input path="firstName"/></td>
</tr>
<tr>
<td>Last Name:</td>
<td><form:input path="lastName"/></td>
</tr>
<tr>
<td colspan="2" align="center"><input type="submit" value="Save"></td>
</tr>
</table>
</form:form>
From jsp page we see that I didn't declare variable 'description', but when update my existing data the variable 'description' become null. I have tried using #DynamicUpdate or related to dynamic update process, but the result was still the same, the variable 'description' still become null.
Any suggestion?

Answer 1

The problem is that the way your controller is written: a new Model instance is created
and populated on execution of saveData.
You can update your code to be like the below. Now on POST the Model instance
will be that returned from getModel() rather than a new instance and only the
values specified in the incoming request wil be updated. We can also update the GET to use the same code to populate the model.
Essentially then:
on GET - the model will be populated for the UI by a call to #ModelAttribute
on POST - the model will be populated and the Model instance returned will be passed to saveData();
See:
https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html#mvc-ann-modelattrib-method-args
#Controller
public class ModelController {
#Autowired
ModelService modelService
#RequestMapping(value="/editModel", method.RequestMethod.GET)
public String formCreator(HttpServletRequest request) {
return "editModel"
}
#RequestMapping(value="/saveModel", method.RequestMethod.POST)
public String saveData(#ModelAttribute("modelData") Model model) {
//you can have 1 method in your service and DAO
//DAO can use saveOrUpdate() method of session;
modelService.persist(model);
return "redirect:/modelList";
}
#ModelAttribute("modelData")
public Model getModel(#RequestParam(name = "id", required = false)Integer id){
return id != null ? modelService.get(id) : new Model();
}
}