spring JPA CRUD Repository and updating a record - spring

Question

This is a question about a Spring Boot MVC application with Hibernate and PostgreSQL.
I have a web page that allows a user to set administrative / configuration data for an application, and I want to store this data in a single database record. I have a POJO to contain the data. I have coded up a Spring MVC app that persists this data.
The trouble is that each time the user saves the data (by doing a POST from the web page) the Spring application creates a new record in the database.
I'm using a Repository, and I was under the impression that each time I did a Repository.save() on the object it would update the existing record if there is one, otherwise create a new one and that it would identify the record based upon the primary key. I could not find an "update" method.
I have tried several ways around this issue but they either still make extra records, fail with a duplicate key error or just plain don't work.
Also, it seems that each time I start the web page or the application all the data in the database is removed.
So what's the trick? Thanks very much...
Here is my code:
AdminFormController.java
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.beans.factory.annotation.Autowired;
#Controller
public class Admin_FormController
{
#Autowired
private AdminDataRepository rep;
#RequestMapping(value="/admin", method=RequestMethod.GET)
public String adminForm(Model model)
{
AdminData ad = new AdminData();
model.addAttribute("adminForm", ad);
ad = rep.findById(1L);
if(ad != null)
ad.setId(1L);
return "adminForm";
}
#RequestMapping(value="/admin", method=RequestMethod.POST)
public String adminSubmit(#ModelAttribute AdminData ad, Model model)
{
// ad.setId(1L);;
rep.save(ad);
model.addAttribute("adminForm", ad);
return "adminForm";
}
}
AdminDataRepository.java
import org.springframework.data.repository.CrudRepository;
public interface AdminDataRepository extends CrudRepository<AdminData, String>
{
AdminData findById(Long Id);
}
AdminData.java
import java.util.logging.Logger;
import javax.persistence.*;
#Entity
public class AdminData
{
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;
private String useDates;
private String startDate;
private String endDate;
public String getUseDates()
{
return useDates;
}
public String getStartDate()
{
return startDate;
}
public String getEndDate()
{
return endDate;
}
public void setUseDates(String s)
{
Logger.getGlobal().info(() -> "UseDates: " + s);
useDates = s;
}
public void setStartDate(String s)
{
Logger.getGlobal().info(() -> "Start Date: " + s);
startDate = s;
}
public void setEndDate(String s)
{
Logger.getGlobal().info(() -> "End Date: " + s);
endDate = s;
}
}

Answer 1

You need to store the object somewhere between requests. Your options:
Using hidden form fields
Re-read it from the database (in your POST method)
Use session
1 is inconvenient, and not secure. 2 Doesn't support concurrency control. 3 is secure and correct.
To implement #3, add #SessionAttributes("yourAttributeName") just before your controller. Add a SessionStatus parameter to your POST method, and call sessionStatus.setComplete() when you're done with it.
Example here.