Dependent drop-down list from map in Thymeleaf

Question

I want to create a drop-down list with countries and the second drop-down list with cities, which depends on selected value in the first list. And the list of cities should be changed dynamically. In the view (Thymeleaf) I have a Map<CountryModel, Set<RegionModel>> from controller. CountryModel's name should be shows in the second drop-down list, and Set should be shows in the second(dependent) drop-down list.
Here I create first drop-down list:

 <tr>
   <td th:text="#{country}"/>
   <td>
      <div class="form-group">
          <select th:field="*{transferRequestModel.country}" class="form-control" id="country">
                <option th:each="country : ${transferModel.countries}"
                    th:value="${country}"
                    th:text="${country.key.countryName}">Wireframe
                </option>
          </select>
      </div>
    </td>
 </tr>

So how to create second drop-down list which depends on selected country in the first list?

Answer 1

In our project we did it like that:

<div class="form-group">
    <label class="col-sm-4 control-label" 
           th:text="#{person.edit.policy.tfoms}"></label>

    <div class="col-sm-8">
        <select class="form-control" th:field="*{tfoms}" 
                onchange="loadInsuranceCompanies()">
            <option th:each="t : ${tfomses}" 
                    th:value="${t.uidtfoms}"  
                    th:text="${t.shortName}"
                    th:selected="${personBean.tfoms != null 
                    and personBean.tfoms.equals(t)}">
            </option>
        </select>
    </div>
</div>
<div th:class="${#fields.hasErrors('insuranceCompany')} 
     ? 'form-group has-error' : 'form-group'">
    <label class="col-sm-4 control-label" 
          th:text="#{person.edit.policy.ic}">
    </label>

    <div class="col-sm-8" id="insuranceCompaniesContent">
        <select class="form-control" id="insuranceCompany" 
                name="insuranceCompany"  
                th:fragment="insuranceCompany">
            <option th:each="i : ${insuranceCompanies}" 
                    th:value="${i.uidinsurancecompany}"  
                    th:text="${i.shortName}"
                    th:selected="${personBean.insuranceCompany != null 
                    and personBean.insuranceCompany.equals(i)}">
            </option>
        </select>
        <div th:if="${#fields.hasErrors('insuranceCompany')}" 
         th:each="err : ${#fields.errors('insuranceCompany')}">
        <span class="text-danger" th:text="${err}"></span><br/>
        </div>
    </div>
</div>

Insurance companies loading function loadInsuranceCompanies():

function loadInsuranceCompanies() {
    var url = /*[[@{/PersonEdit/insuranceCompanies}]]*/ "/PersonEdit/insuranceCompanies";
    if ($('#tfoms').val() !== '') {
        url = url + '/' + $('#tfoms').val();
    }
    $("#insuranceCompaniesContent").load(url);
}

And finally code in controller:

@RequestMapping(value = "/PersonEdit/insuranceCompanies/{tfoms}", method = RequestMethod.GET)
public String getInsuranceCompaniesByTfoms(@PathVariable("tfoms") Integer tfomsId,
        Model model) {
    model.addAttribute("insuranceCompanies", insuranceCompanyService
            .getInsuranceCompaniesByTfoms(new TerritorialFondOms(tfomsId)));
    return "person/PersonEdit :: insuranceCompany";
}

Answer 2

So I have solved my problem with AJAX request and jQuery append.

1. Change Map<CountryModel, Set<RegionModel>> to Map<String, Set<String>>

2. AJAX request

   function sendAjaxRequest() {
       var country = $("#country").val();
       $.get( "/regions?country=" + country, function( data ) {
           $("#region").empty();
           data.forEach(function(item, i) {
               var option = "<option value = " + item + ">" + item +  "</option>";
               $("#region").append(option);
           });
       });
   };
   

3. Use sendAjaxRequest() when i change first drop-down list.

   $(document).ready(function() {
       $("#country").change(function() {
           sendAjaxRequest();
       });
   });
   

4. Drop-down list at the Thymeleaf template

First drop-down list

<td th:text="#{country}"/>
<td>
    <div class="form-group">
        <select th:field="*{model.country}" class="form-control" id="country">
            <option th:each="country : ${model.countries}"
                    th:value="${country}"
                    th:text="${country}">Wireframe
            </option>
        </select>
    </div>
</td>

Second drop-down list

<td>
    <div class="form-group">
        <select th:field="*{requestModel.region}" class="form-control" id="region">
        </select>
    </div>
</td>

5. Controller

   @RequestMapping(value = "/regions")
   @ResponseBody
   public Set getRegions(@RequestParam String country) {
       Map<String, Set<String>> regions = regionsService.getRegions();
       return regions.get(country);
   }