unobtrusive MVC3 validating group of checkboxes - asp.net-mvc

Question

I need to validate a group of checkboxes using MVC3 unobtrusive validation. how would i do it? I found this and tried it, but it doesn't work.
$(function(){
$.validator.addMethod('cb_selectone', function(value,element){
if(element.length>0){
for(var i=0;i<element.length;i++){
if($(element[i]).val('checked')) return true;
}
return false;
}
return false;
}, 'Please select at least one option');
$('#main').validate({rules:{Services:"cb_selectone"}});
...
My Html:
<input type="checkbox" class="checkbox" name="Services" value="1" />
<input type="checkbox" class="checkbox" name="Services" value="2" />
<input type="checkbox" class="checkbox" name="Services" value="3" />
It would be best if someone provided a complete solution with server side + client side validation (of course using MVC3 unobtrusive validation).
Thanks

Answer 1

Ok, figured it out:
for server validation:
using data annotations (required will do it)
like so in my view model:
[Required(ErrorMessageResourceName = "fld_Service_val_Required_lbl", ErrorMessageResourceType = typeof(Resources.Service.Controllers.Firm))]
public ICollection<int> Services { get; set; }
for client validation in my html i added a class to my input checkboxes:
<input type="checkbox" class="checkbox required-checkbox" name="Services" value="1" />
<input type="checkbox" class="checkbox required-checkbox" name="Services" value="2" />
<input type="checkbox" class="checkbox required-checkbox" name="Services" value="3" />
and also:
$(function(){
$.validator.addMethod('required_group', function(value, element) {
var $module = $(element).parents('form');
return $module.find('input.checkbox:checked').length;
}, 'Select at least one Service please');
$.validator.addClassRules('required-checkbox', { 'required_group' : true });
..
not sure if this is the best solution but it works :). if someone knows a better please post.

Answer 2

This works - validates appropriately on submit, and hides/displays the validation message if a checkbox is subsequently checked or unchecked with minimal overhead (only gets hit once per validation cycle).
JavaScript:
(function ($) {
//functions from unobtrusive:
function setValidationValues(options, ruleName, value) {
options.rules[ruleName] = value;
if (options.message) {
options.messages[ruleName] = options.message;
}
}
var formEls;
function getUniqueFormId(form) {
if (typeof(formEls==='undefined')) {
formEls = document.getElementsByTagName('form');
}
return 'form' + Array.prototype.indexOf.call(formEls, form);
}
//from jQuery validation
function findByName(name, form) {
// select by name and filter by form for performance over form.find("[name=...]")
return $(document.getElementsByName(name)).map(function (index, element) {
return element.form == form && element.name == name && element || null;
});
}
//-------------------------
$.validator.addMethod('requiredgroup', function (value, element, params) {
for (var i = 0; i < params.length; i++) {
if (params[i].checked) { return true; }
}
return false;
});
valGroups = [];
$.validator.unobtrusive.adapters.add('requiredgroup', function (options) {
var groupName = options.element.name,
uniqueGroup = getUniqueFormId(options.form) + groupName;
if (!valGroups[uniqueGroup]) {
valGroups[uniqueGroup] = findByName(groupName, options.form);
}
//jQuery Validation Plugin 1.9.0 only ever validates first chekcbox in a list
//could probably work around setting this for every element:
setValidationValues(options, 'requiredgroup', valGroups[uniqueGroup]);
});
} (jQuery));
of course the elements must have a data-val-requiredgroup attribute. The following MVC code (as part of a helper) will add the appropriate annotations:
var metaData = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
string name = ExpressionHelper.GetExpressionText(expression);
var baseAttr = htmlHelper.GetUnobtrusiveValidationAttributes(name, metaData);
baseAttr.Add("name", name);
baseAttr.Add("type", "checkbox");
if (metaData.IsRequired)
{
baseAttr.Add("data-val-requiredgroup", baseAttr["data-val-required"]);
baseAttr.Remove("data-val-required");
Because it looks for the Required attribute, server side validation is handled by the existing framework.