如何在jqgrid上实现搜索？

jQuery("#grid_id").jqGrid({
    url: 'mydata.json',
    datatype: 'json',
    colNames: ['Column 1', 'Column 2', 'Column 3'],
    colModel: [
        { name: 'col1', searchoptions: { sopt: ['eq', 'ne', 'cn'] }, stype: 'text' },
        { name: 'col2', searchoptions: { sopt: ['eq', 'ne', 'cn'] }, stype: 'text' },
        { name: 'col3', searchoptions: { sopt: ['eq', 'ne', 'cn'] }, stype: 'text' }
    ],
    search: true,
    pager: '#pager'
});

jQuery("#grid_id").jqGrid('navGrid', '#pager', { search: true });

function searchGrid() {
    var postdata = jQuery("#grid_id").jqGrid('getGridParam', 'postData');
    jQuery("#grid_id").jqGrid('setGridParam', { search: true });
    jQuery("#grid_id").jqGrid('filterGrid', postdata, refresh);
}

jQuery("#grid_id").jqGrid({
    url: 'mydata.json',
    datatype: 'json',
    colNames: ['Column 1', 'Column 2', 'Column 3'],
    colModel: [
        { name: 'col1', search: true },
        { name: 'col2', search: true },
        { name: 'col3', search: true }
    ],
    pager: '#pager'
});

jQuery("#search_button").click(function() {
    var search_col1 = jQuery("#search_col1").val();
    var search_col2 = jQuery("#search_col2").val();
    var search_col3 = jQuery("#search_col3").val();

    var postdata = jQuery("#grid_id").jqGrid('getGridParam', 'postData');
    postdata.filters = '{"groupOp":"AND","rules":[';

    if (search_col1) {
        postdata.filters += '{"field":"col1","op":"cn","data":"' + search_col1 + '"},';
    }

    if (search_col2) {
        postdata.filters += '{"field":"col2","op":"cn","data":"' + search_col2 + '"},';
    }

    if (search_col3) {
        postdata.filters += '{"field":"col3","op":"cn","data":"' + search_col3 + '"},';
    }

    postdata.filters = postdata.filters.slice(0, -1) + ']}';

    jQuery("#grid_id").jqGrid('setGridParam', { search: true, postData: postdata });
    jQuery("#grid_id").jqGrid('filterGrid', postdata, refresh);
});