jquery validation plugin : validate with some condition

I m using jquery validator plugin. i need to validate some field with some condition. how do we apply that?

i have a form where user select a country..then user creates branch on the fly, now i want to validate that if user do not select a county then prompt to select country and if user select a country then prompt to create atleast one branch.

what i do as far

if user create any branch then there is a hidden field of counting branch. but that field is filled after creating branch, before that( on page load ) is has no value so if i validate for that hidden field then it always return true. what should i do

here is code snippet i have used but i know there must be a better way to manipulate all above..please suggest me optimize way to do this

<script type="text/javascript">
jQuery.metadata.setType("attr", "validate");

jQuery('#createForm').submit(function(){
        if(jQuery("#hasbranch").val()== 0 ){
            jQuery(".brancherror").html('Atleast one branch is necessary');
            return false;
        }
    });

var validator=jQuery("#createForm").validate({
               rules: { list of rules},
               messgae : { list of messages },                                
});
</script>

<form name="createForm" id="createForm">
<table>
<tr>
      <td>Select Country :<开发者_运维技巧/td>
      <td >
      <select name="country_id" id="country"  class="selectbox" onchange="return showBranch();"     title="Please select country" validate="required:true"  >
    <option value="" >Select Country </option>
    <?php foreach($this->country as $key => $country) { ?>
    <option value="<?php echo $country->id; ?>"<?php if ($country->id == $this->ad_data['country_id']) {?> selected="selected" <?php } ?> > <?php echo $country->name; ?></option> 
    <?php } // end of foreach ?>
      </select>
      </td>
  </tr>
  <tr>
      <td> //Here is link to add branch (via iframe) </td>
  </tr>    
  </table>
   <input type="hidden" value="<?php echo count($_SESSION['branches'])? 1: 0 ;?> name="hasbranch" id="hasbranch" />
   </form>  

You could use depends on rule to apply a conditional validation:

rules: {
    someField: {
       required: true,
       email: {
           depends: function(element) {
               // require someField to be a valid email only if the user checked 
               // to be contacted by email
               return $("#contactform_email:checked");
           }
       }
    }
}