$(document).ready(function(){

            function load_data(query=''){
                $.ajax({
                    url:"main",
                    method: "POST",
                    data:{query:query},
                    success:function(data){
                        $('#tbody').html(data);
                    }
                })
            }

            $('#contract_id').change(function(){
                $('#contrId').val($('#contract_id').val());
                var query = $('#contrId').val();
                load_data(query);
            });

        });