Spring 3 MVC: one-to-many within a dynamic form (a

Question

I'm looking for a solution to manage a one-to-many relation within an HTML form using jQuery. I'm developing with Spring, Spring MVC and Hibernate. I found many tracks on the web, but not any working full-example.

The background

I've three JPA entities:

Consult.java (1)

@Entity
@Table(name = "consult")
public class Consult

    private Integer id;
    private String label;
    private Set<ConsultTechno> consultTechnos;

    /* getters & setters */

}

ConsultTechno.java (2)

@Entity
@Table(name = "consult_techno")
public class ConsultTechno {

    private Integer id;
    private Techno techno;
    private Consult consult;
    private String level;

    /* getters & setters */

}

Techno.java (3)

@Entity
@Table(name="techno")
public class Techno {

    private Integer id;
    private String label;
    private Set<ConsultTechno> consultTechnos;

    /* getters & setters */

}

As shown, a Consult (1) contains n ConsultTechnos (2), which are caracterized by a level and a Techno (3).

The needs

Using an HTML form, I would like to have a Add a techno button which dynamically adds two fields in the DOM:

<input type="text" name="consult.consultTechnos[].techno.id" />
<input type="text" name="consult.consultTechnos[].level" />

Of course, each time the user clicks on the button, those two fields should be re-added, etc. I chose input type="text" for the example, but at the end, the fields will be two select.

Four kinds of operation should be covered:

1. Add a child entity when creating a new master entity
2. Remove a child entity when creating a new master entity
3. Add a child entity when updating a new master entity
4. Remove a child entity when updating a new master entity

The problem

That layout part already works, but when posting the form, I can't manage to bind the dynamically added fields to my @ModelAttribute consult.

Do you have any idea of how to do that kind of jobs? I hope I've been clear enough...

Thanks in advance :)

Answer 1

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

1. Use a List instead of a Set for your one-to-many relations which should be dynamically managed.

2. Initialize your List as an AutoPopulatingList. It's a lazy list which allows to add dynamically elements.

3. 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.

4. 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 :)

Answer 2

why u are using HTML input tag instead of spring taglib forms

   <form:form action="yourURL.htm" command="employeeDto">
    <form:input type="text" name="consult.consultTechnos[].techno.id" />
    <form:input type="text" name="consult.consultTechnos[].level" /> 
   <form:form>

and create one EmployeeDto class like, and add the modelMap.addAttribute("employeeDto", new Employee); in your controller

Answer 3

Well i just got to the problem, the html view source will not show the dynamic html added. If you will inspect the html elements the DOM tree will show you all the dynamic elements added but on the Form Submit if you see all the elements will be submitted to the server including the dynamic created elements too.

One way to reproduce is ob form submit call the javascript method and put a debug point in the javascript method and check for the form submit values in the document>form elements by inspecting the DOM tree