validation for at least one checkbox

Working demo http://jsfiddle.net/RGUTv/

Updated – 12 Jan 2015 => http://jsfiddle.net/r24kcvz6/ CDN was cahnged http://ajax.aspnetcdn.com/ajax/jquery.validate/1.13.1/jquery.validate.js – you can replicate the behaviour by deselcting all the checkboxes and clicking on the submit button.

• http://jqueryvalidation.org/#latest-files-on-jsdelivr-cdn-%28hotlinking-welcome%29:

code

$.validator.addMethod('require-one', function(value) {
    return $('.require-one:checked').size() > 0;
}, 'Please check at least one box.');

var checkboxes = $('.require-one');
var checkbox_names = $.map(checkboxes, function(e, i) {
    return $(e).attr("name")
}).join(" ");

$("#itemForm").validate({
    groups: {
        checks: checkbox_names
    },
    errorPlacement: function(error, element) {
        if (element.attr("type") == "checkbox") error.insertAfter(checkboxes.last());
        else error.insertAfter(element);
    }
});

html

<form name="itemForm" id="itemForm" method="post">

<label for="river1">river1</label>
<input checked="checked" data-val="true" data-val-required="The     river1 field is required." id="river1" name="river1" type="checkbox" value="true" class="require-one" />
<input name="river1" type="hidden" value="false" /><br />

<label for="river2">river2</label>
<input checked="checked" data-val="true" data-val-required="The river2 field is required." id="river2" name="river2" type="checkbox" value="true" class="require-one" />
<input name="river2" type="hidden" value="false" /><br />

<label for="river3">river3</label>
<input checked="checked" data-val="true" data-val-required="The river3 field is required." id="river3" name="river3" type="checkbox" value="true" class="require-one" />
<input name="river3" type="hidden" value="false" /><br />

<input type="submit" />
</form>

Image if you un-tick the validation will trigger