This point is still quite confusing and unclear on the web, so here is the way I solved my problem. This solution is probably not the most optimized one, but it works when creating and updating a master entity.
Theory
Use a List instead of a Set for your one-to-many relations which should be dynamically managed.
Initialize your List as an AutoPopulatingList. It's a lazy list which allows to add dynamically elements.
Add an attribute remove of int to your child entity. This will play the part of a boolean flag and will be usefull when removing dynamically an element.
When posting the form, persist only the elements that have the flag remove on 0 (i.e. false).
Practice
A working full-example: an employer has many employees, an employee has one employer.
Entities:
Employer.java
@Entity
@Table(name = "employer")
public class Employer
private Integer id;
private String firstname;
private String lastname;
private String company;
private List<Employee> employees; // one-to-many
/* getters & setters */
}
Employee.java
@Entity
@Table(name = "employee")
public class Employee {
private Integer id;
@Transient // means "not a DB field"
private Integer remove; // boolean flag
private String firstname;
private String lastname;
private Employer employer; // many-to-one
/* getters & setters */
}
Controller:
EmployerController.java
@Controller
@RequestMapping("employer")
public class EmployerController {
// Manage dynamically added or removed employees
private List<Employee> manageEmployees(Employer employer) {
// Store the employees which shouldn't be persisted
List<Employee> employees2remove = new ArrayList<Employee>();
if (employer.getEmployees() != null) {
for (Iterator<Employee> i = employer.getEmployees().iterator(); i.hasNext();) {
Employee employee = i.next();
// If the remove flag is true, remove the employee from the list
if (employee.getRemove() == 1) {
employees2remove.add(employee);
i.remove();
// Otherwise, perform the links
} else {
employee.setEmployer(employer);
}
}
}
return employees2remove;
}
// -- Creating a new employer ----------
@RequestMapping(value = "create", method = RequestMethod.GET)
public String create(@ModelAttribute Employer employer, Model model) {
// Should init the AutoPopulatingList
return create(employer, model, true);
}
private String create(Employer employer, Model model, boolean init) {
if (init) {
// Init the AutoPopulatingList
employer.setEmployees(new AutoPopulatingList<Employee>(Employee.class));
}
model.addAttribute("type", "create");
return "employer/edit";
}
@RequestMapping(value = "create", method = RequestMethod.POST)
public String create(@Valid @ModelAttribute Employer employer, BindingResult bindingResult, Model model) {
if (bindingResult.hasErrors()) {
// Should not re-init the AutoPopulatingList
return create(employer, model, false);
}
// Call the private method
manageEmployees(employer);
// Persist the employer
employerService.save(employer);
return "redirect:employer/show/" + employer.getId();
}
// -- Updating an existing employer ----------
@RequestMapping(value = "update/{pk}", method = RequestMethod.GET)
public String update(@PathVariable Integer pk, @ModelAttribute Employer employer, Model model) {
// Add your own getEmployerById(pk)
model.addAttribute("type", "update");
return "employer/edit";
}
@RequestMapping(value = "update/{pk}", method = RequestMethod.POST)
public String update(@PathVariable Integer pk, @Valid @ModelAttribute Employer employer, BindingResult bindingResult, Model model) {
// Add your own getEmployerById(pk)
if (bindingResult.hasErrors()) {
return update(pk, employer, model);
}
List<Employee> employees2remove = manageEmployees(employer);
// First, save the employer
employerService.update(employer);
// Then, delete the previously linked employees which should be now removed
for (Employee employee : employees2remove) {
if (employee.getId() != null) {
employeeService.delete(employee);
}
}
return "redirect:employer/show/" + employer.getId();
}
// -- Show an existing employer ----------
@RequestMapping(value = "show/{pk}", method = RequestMethod.GET)
public String show(@PathVariable Integer pk, @ModelAttribute Employer employer) {
// Add your own getEmployerById(pk)
return "employer/show";
}
}
View:
employer/edit.jsp
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"
%><%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"
%><%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions"
%><%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"
%><!DOCTYPE HTML>
<html>
<head>
<title>Edit</title>
<style type="text/css">.hidden {display: none;}</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.2/jquery.min.js"></script>
<script type="text/javascript">
$(function() {
// Start indexing at the size of the current list
var index = ${fn:length(employer.employees)};
// Add a new Employee
$("#add").off("click").on("click", function() {
$(this).before(function() {
var html = '<div id="employees' + index + '.wrapper" class="hidden">';
html += '<input type="text" id="employees' + index + '.firstname" name="employees[' + index + '].firstname" />';
html += '<input type="text" id="employees' + index + '.lastname" name="employees[' + index + '].lastname" />';
html += '<input type="hidden" id="employees' + index + '.remove" name="employees[' + index + '].remove" value="0" />';
html += '<a href="#" class="employees.remove" data-index="' + index + '">remove</a>';
html += "</div>";
return html;
});
$("#employees" + index + "\\.wrapper").show();
index++;
return false;
});
// Remove an Employee
$("a.employees\\.remove").off("click").on("click", function() {
var index2remove = $(this).data("index");
$("#employees" + index2remove + "\\.wrapper").hide();
$("#employees" + index2remove + "\\.remove").val("1");
return false;
});
});
</script>
</head>
<body>
<c:choose>
<c:when test="${type eq 'create'}"><c:set var="actionUrl" value="employer/create" /></c:when>
<c:otherwise><c:set var="actionUrl" value="employer/update/${employer.id}" /></c:otherwise>
</c:choose>
<form:form action="${actionUrl}" modelAttribute="employer" method="POST" name="employer">
<form:hidden path="id" />
<table>
<tr>
<td><form:label path="firstname">Firstname</form:label></td>
<td><form:input path="firstname" /><form:errors path="firstname" /></td>
</tr>
<tr>
<td><form:label path="lastname">Lastname</form:label></td>
<td><form:input path="lastname" /><form:errors path="lastname" /></td>
</tr>
<tr>
<td><form:label path="company">company</form:label></td>
<td><form:input path="company" /><form:errors path="company" /></td>
</tr>
<tr>
<td>Employees</td>
<td>
<c:forEach items="${employer.employees}" varStatus="loop">
<!-- Add a wrapping div -->
<c:choose>
<c:when test="${employer.employees[loop.index].remove eq 1}">
<div id="employees${loop.index}.wrapper" class="hidden">
</c:when>
<c:otherwise>
<div id="employees${loop.index}.wrapper">
</c:otherwise>
</c:choose>
<!-- Generate the fields -->
<form:input path="employees[${loop.index}].firstname" />
<form:input path="employees[${loop.index}].lastname" />
<!-- Add the remove flag -->
<c:choose>
<c:when test="${employees[loop.index].remove eq 1}"><c:set var="hiddenValue" value="1" /></c:when>
<c:otherwise><c:set var="hiddenValue" value="0" /></c:otherwise>
</c:choose>
<form:hidden path="employees[${loop.index}].remove" value="${hiddenValue}" />
<!-- Add a link to remove the Employee -->
<a href="#" class="employees.remove" data-index="${loop.index}">remove</a>
</div>
</c:forEach>
<button id="add" type="button">add</button>
</td>
</tr>
</table>
<button type="submit">OK</button>
</form:form>
</body>
</html>
Hope that could help :)
