I need to modify a php search script so that it can handle multiple entries for a single field. The search engine is designed for a real estate website. The current search form allows users to search for houses by selecting a single neighborhood from a dropdown menu. Instead of a dropdown menu, I would like to use a list of checkboxes so that the the user can search for houses in multiple neighborhoods at one time. I have converted all of the dropdown menu items into checkboxes on the HTML side but the PHP script only searches for houses in the last checkbox selected. For example, if I selected: 'Dallas' 'Boston' 'New York' the search engine will only search for houses in New York.

Im new to PHP, so I am a little at a loss as to how to modify this script to handle the behavior I have described:

<?php

    require_once(dirname(__FILE__).'/extra_search_fields.php');

    //Add Widget for configurable search.
    add_action('plugins_loaded',array('DB_CustomSearch_Widget','init'));


    class DB_CustomSearch_Widget extends DB_Search_Widget {
        function DB_CustomSearch_Widget($params=array()){
            DB_CustomSearch_Widget::__construct($params);
        }
        function __construct($params=array()){
            $this->loadTranslations();
            parent::__construct(__('Custom Fields ','wp-custom-fields-search'),$params);
            add_action('admin_print_scripts', array(&$this,'print_admin_scripts'), 90);
            add_action('admin_menu', array(&$this,'plugin_menu'), 90);
            add_filter('the_content', array(&$this,'process_tag'),9);
            add_shortcode( 'wp-custom-fields-search', array(&$this,'process_shortcode') );
            wp_enqueue_script('jquery');
            if(version_compare("2.7",$GLOBALS['wp_version'])>0) wp_enqueue_script('dimensions');
        }
        function init(){
            global $CustomSearchFieldStatic;
            $CustomSearchFieldStatic['Object'] = new DB_CustomSearch_Widget();
            $CustomSearchFieldStatic['Object']->ensureUpToDate();
        }

        function currentVersion(){
            return "0.3.16";
        }

        function ensureUpToDate(){
            $version = $this->getConfig('version');
            $latest = $this->currentVersion();
            if($version<$latest) $this->upgrade($version,$latest);
        }

        function upgrade($current,$target){
            $options = $this->getConfig();
            if(version_compare($current,"0.3")<0){
                $config = $this->getDefaultConfig();
                $config['name'] = __('Default Preset','wp-custom-fields-search');
                $options['preset-default'] = $config;
            }
            $options['version']=$target;
            update_option($this->id,$options);
        }

        function getInputs($params = false,$visitedPresets=array()){
            if(is_array($params)){
                $id = $params['widget_id'];
            } else {
                $id = $params;
            }
            if($visitedPresets[$id]) return array();
            $visitedPresets[$id]=true;

            global $CustomSearchFieldStatic;
            if(!$CustomSearchFieldStatic['Inputs'][$id]){

                $config = $this->getConfig($id);
                $inputs = array();
                if($config['preset']) $inputs = $this->getInputs($config['preset'],$visitedPresets);
                $nonFields = $this->getNonInputFields();
                if($config)
                foreach($config as $k=>$v){
                    if(in_array($k,$nonFields)) continue;
                    if(!(class_exists($v['input']) && class_exists($v['comparison']) && class_exists($v['joiner']))) {
                        continue;
                    }
                    $inputs[] =  new CustomSearchField($v);

                }
                foreach($inputs as $k=>$v){
                    $inputs[$k]->setIndex($k);
                }
                $CustomSearchFieldStatic['Inputs'][$id]=$inputs;
            }
            return $CustomSearchFieldStatic['Inputs'][$id];
        }
        function getTitle($params){
            $config = $this->getConfig($params['widget_id']);
            return $config['name'];
        }

        function form_processPost($post,$old){
            unset($post['###TEMPLATE_ID###']);
            if(!$post) $post=array('exists'=>1);
            return $post;
        }
        function getDefaultConfig(){
            return array('name'=>'Site Search', 
                1=>array(
                    'label'=>__('Key Words','wp-custom-fields-search'),
                    'input'=>'TextField',
                    'comparison'=>'WordsLikeComparison',
                    'joiner'=>'PostDataJoiner',
                    'name'=>'all'
                ),
                2=>array(
                    'label'=>__('Category','wp-custom-fields-search'),
                    'input'=>'DropDownField',
                    'comparison'=>'EqualComparison',
                    'joiner'=>'CategoryJoiner'
                ),
            );
        }
        function form_outputForm($values,$pref){
            $defaults=$this->getDefaultConfig();
            $prefId = preg_replace('/^.*\[([^]]*)\]$/','\\1',$pref);
            $this->form_existsInput($pref);
            $rand = rand();
?>
    <div id='config-template-<?php echo $prefId?>' style='display: none;'>
    <?php 
        $templateDefaults = $defaults[1];
        $templateDefaults['label'] = 'Field ###TEMPLATE_ID###';
        echo  $this->singleFieldHTML($pref,'###TEMPLATE_ID###',$templateDefaults);
    ?>
    </div>

<?php
            foreach($this->getClasses('input') as $class=>$desc) {
                if(class_exists($class))
                    $form = new $class();
                else $form = false;
                if(compat_method_exists($form,'getConfigForm')){
                    if($form = $form->getConfigForm($pref.'[###TEMPLATE_ID###]',array('name'=>'###TEMPLATE_NAME###'))){
?>
    <div id='config-input-templates-<?php echo $class?>-<?php echo $prefId?>' style='display: none;'>
        <?php echo $form?>
    </div>

<?php                   }
                }
            }
 ?>
    <div id='config-form-<?php echo $prefId?>'>
<?php
            if(!$values) $values = $defaults;
            $maxId=0;
            $presets = $this->getPresets();
            array_unshift($presets,__('NONE','wp-custom-fields-search'));
?>
        <div class='searchform-name-wrapper'><label for='<?php echo $prefId?>[name]'><?php echo __('Search Title','wp-custom-fields-search')?></label><input type='text' class='form-title-input' id='<?php echo $prefId?>[name]' name='<?php echo $pref?>[name]' value='<?php echo $values['name']?>'/></div>
        <div class='searchform-preset-wrapper'><label for='<?php echo $prefId?>[preset]'><?php echo __('Use Preset','wp-custom-fields-search')?></label>
<?php
            $dd = new AdminDropDown($pref."[preset]",$values['preset'],$presets);
            echo $dd->getInput()."</div>";
            $nonFields = $this->getNonInputFields();
            foreach($values as $id => $val){
                $maxId = max($id,$maxId);
                if(in_array($id,$nonFields)) continue;
                echo "<div id='config-form-$prefId-$id'>".$this->singleFieldHTML($pref,$id,$val)."</div>";
            }
?>
    </div>

    <br/><a href='#' onClick="return CustomSearch.get('<?php echo $prefId?>').add();"><?php echo __('Add Field','wp-custom-fields-search')?></a>
    <script type='text/javascript'>
            CustomSearch.create('<?php echo $prefId?>','<?php echo $maxId?>');
<?php
    foreach($this->getClasses('joiner') as $joinerClass=>$desc){
        if(compat_method_exists($joinerClass,'getSuggestedFields')){
            $options = eval("return $joinerClass::getSuggestedFields();");
            $str = '';
            foreach($options as $i=>$v){
                $k=$i;
                if(is_numeric($k)) $k=$v;
                $options[$i] = json_encode(array('id'=>$k,'name'=>$v));
            }
            $str = '['.join(',',$options).']';
            echo "CustomSearch.setOptionsFor('$joinerClass',".$str.");\n";
        }elseif(eval("return $joinerClass::needsField();")){
            echo "CustomSearch.setOptionsFor('$joinerClass',[]);\n";
        }
    }
?>
    </script>
<?php
        }

        function getNonInputFields(){
            return array('exists','name','preset','version');
        }
        function singleFieldHTML($pref,$id,$values){
            $prefId = preg_replace('/^.*\[([^]]*)\]$/','\\1',$pref);
            $pref = $pref."[$id]";
            $htmlId = $pref."[exists]";
            $output = "<input type='hidden' name='$htmlId' value='1'/>";
            $titles="<th>".__('Label','wp-custom-fields-search')."</th>";
            $inputs="<td><input type='text' name='$pref"."[label]' value='$values[label]' class='form-field-title'/></td><td><a href='#' onClick='return CustomSearch.get(\"$prefId\").toggleOptions(\"$id\");'>".__('Show/Hide Config','wp-custom-fields-search')."</a></td>";
            $output.="<table class='form-field-table'><tr>$titles</tr><tr>$inputs</tr></table>";
            $output.="<div id='form-field-advancedoptions-$prefId-$id' style='display: none'>";
            $inputs='';$titles='';
            $titles="<th>".__('Data Field','wp-custom-fields-search')."</th>";
            $inputs="<td><div id='form-field-dbname-$prefId-$id' class='form-field-title-div'><input type='text' name='$pref"."[name]' value='$values[name]' class='form-field-title'/></div></td>";
            $count=1;
            foreach(array('joiner'=>__('Data Type','wp-custom-fields-search'),'comparison'=>__('Compare','wp-custom-fields-search'),'input'=>__('Widget','wp-custom-fields-search')) as $k=>$v){
                $dd = new AdminDropDown($pref."[$k]",$values[$k],$this->getClasses($k),array('onChange'=>'CustomSearch.get("'.$prefId.'").updateOptions("'.$id.'","'.$k.'")','css_class'=>"wpcfs-$k"));
                $titles="<th>".$v."</th>".$titles;
                $inputs="<td>".$dd->getInput()."</td>".$inputs;
                if(++$count==2){
                    $output.="<table class='form-field-table form-class-$k'><tr>$titles</tr><tr>$inputs</tr></table>";
                    $count=0;
                    $inputs = $titles='';
                }
            }
            if($titles){
                $output.="<table class='form-field-table'><tr>$titles</tr><tr>$inputs</tr></table>";
                $inputs = $titles='';
            }
            $titles.="<th>".__('Numeric','wp-custom-fields-search')."</th><th>".__('Widget Config','wp-custom-fields-search')."</th>";
            $inputs.="<td><input type='checkbox' ".($values['numeric']?"checked='true'":"")." name='$pref"."[numeric]'/></td>";

            if(class_exists($widgetClass = $values['input'])){
                $widget = new $widgetClass();
                if(compat_method_exists($widget,'getConfigForm'))
                    $widgetConfig=$widget->getConfigForm($pref,$values);
            }


            $inputs.="<td><div id='$this->id"."-$prefId"."-$id"."-widget-config'>$widgetConfig</div></td>";
            $output.="<table class='form-field-table'><tr>$titles</tr><tr>$inputs</tr></table>";
            $output.="</div>";
            $output.="<a href='#' onClick=\"return CustomSearch.get('$prefId').remove('$id');\">Remove Field</a>";
            return "<div class='field-wrapper'>$output</div>";
        }

        function getRootURL(){
            return WP_CONTENT_URL .'/plugins/' .  dirname(plugin_basename(__FILE__) ) . '/';
        }
        function print_admin_scripts($params){
            $jsRoot = $this->getRootURL().'js';
            $cssRoot = $this->getRootURL().'css';
            $scripts = array('Class.js','CustomSearch.js','flexbox/jquery.flexbox.js');
            foreach($scripts as $file){
                echo "<script src='$jsRoot/$file' ></script>";
            }
            echo "<link rel='stylesheet' href='$cssRoot/admin.css' >";
            echo "<link rel='stylesheet' href='$jsRoot/flexbox/jquery.flexbox.css' >";
        }

        function getJoiners(){
            return $this->getClasses('joiner');
        }
        function getComparisons(){
            return $this->getClasses('comparison');
        }
        function getInputTypes(){
            return $this->getClasses('input');
        }
        function getClasses($type){
            global $CustomSearchFieldStatic;
            if(!$CustomSearchFieldStatic['Types']){
                $CustomSearchFieldStatic['Types'] = array(
                    "joiner"=>array(
                        "PostDataJoiner" =>__( "Post Field",'wp-custom-fields-search'),
                        "CustomFieldJoiner" =>__( "Custom Field",'wp-custom-fields-search'),
                        "CategoryJoiner" =>__( "Category",'wp-custom-fields-search'),
                        "TagJoiner" =>__( "Tag",'wp-custom-fields-search'),
                        "PostTypeJoiner" =>__( "Post Type",'wp-custom-fields-search'),
                    ),
                    "input"=>array(
                        "TextField" =>__( "Text Input",'wp-custom-fields-search'),
                        "DropDownField" =>__( "Drop Down",'wp-custom-fields-search'),
                        "RadioButtonField" =>__( "Radio Button",'wp-custom-fields-search'),
                        "HiddenField" =>__( "Hidden Constant",'wp-custom-fields-search'),
                    ),
                    "comparison"=>array(
                        "EqualComparison" =>__( "Equals",'wp-custom-fields-search'),
                        "LikeComparison" =>__( "Phrase In",'wp-custom-fields-search'),
                        "WordsLikeComparison" =>__( "Words In",'wp-custom-fields-search'),
                        "LessThanComparison" =>__( "Less Than",'wp-custom-fields-search'),
                        "MoreThanComparison" =>__( "More Than",'wp-custom-fields-search'),
                        "AtMostComparison" =>__( "At Most",'wp-custom-fields-search'),
                        "AtLeastComparison" =>__( "At Least",'wp-custom-fields-search'),
                        "RangeComparison" =>__( "Range",'wp-custom-fields-search'),
//TODO: Make this work...
//                      "NotEqualComparison" =>__( "Not Equal To",'wp-custom-fields-search'),
                    )
                );
                $CustomSearchFieldStatic['Types'] = apply_filters('custom_search_get_classes',$CustomSearchFieldStatic['Types']);
            }
            return $CustomSearchFieldStatic['Types'][$type];
        }
        function plugin_menu(){
            add_options_page('Form Presets','WP Custom Fields Search',8,__FILE__,array(&$this,'presets_form'));
        }
        function getPresets(){
            $presets = array();
            foreach(array_keys($config = $this->getConfig()) as $key){
                if(strpos($key,'preset-')===0) {
                    $presets[$key] = $key;
                    if($name = $config[$key]['name'])
                        $presets[$key]=$name;
                }
            }
            return $presets;
        }
        function presets_form(){
            $presets=$this->getPresets();
            if(!$preset = $_REQUEST['selected-preset']){
                $preset = 'preset-default';
            }
            if(!$presets[$preset]){
                $defaults = $this->getDefaultConfig();
                $options = $this->getConfig();
                $options[$preset] = $defaults;
                if($n = $_POST[$this->id][$preset]['name'])
                    $options[$preset]['name'] = $n;
                elseif($preset=='preset-default')
                    $options[$preset]['name'] = 'Default';
                else{
                    list($junk,$id) = explode("-",$preset);
                    $options[$preset]['name'] = 'New Preset '.$id;
                }
                update_option($this->id,$options);
                $presets[$preset] = $options[$preset]['name'];
            }
            if($_POST['delete']){
                check_admin_referer($this->id.'-editpreset-'.$preset);
                $options = $this->getConfig();
                unset($options[$preset]);
                unset($presets[$preset]);
                update_option($this->id,$options);
                list($preset,$name) = each($presets);
            }

            $index = 1;
            while($presets["preset-$index"]) $index++;
            $presets["preset-$index"] = __('New Preset','wp-custom-fields-search');

            $linkBase = $_SERVER['REQUEST_URI'];
            $linkBase = preg_replace("/&?selected-preset=[^&]*(&|$)/",'',$linkBase);
            foreach($presets as $key=>$name){
                $config = $this->getConfig($key);
                if($config && $config['name']) $name=$config['name'];
                if(($n = $_POST[$this->id][$key]['name'])&&(!$_POST['delete']))
                    $name = $n;
                $presets[$key]=$name;
            }
            $plugin=&$this;
            ob_start();
            wp_nonce_field($this->id.'-editpreset-'.$preset);
            $hidden = ob_get_contents();
            $hidden.="<input type='hidden' name='selected-preset' value='$preset'>";
            $shouldSave = $_POST['selected-preset'] && !$_POST['delete'] && check_admin_referer($this->id.'-editpreset-'.$preset);
            ob_end_clean();
            include(dirname(__FILE__).'/templates/options.php');
        }
        function process_tag($content){
            $regex = '/\[\s*wp-custom-fields-search\s+(?:([^\]=]+(?:\s+.*)?))?\]/';
            return preg_replace_callback($regex, array(&$this, 'generate_from_tag'), $content);
        }
        function process_shortcode($atts,$content){
            return $this->generate_from_tag(array("",$atts['preset']));
        }
        function generate_from_tag($reMatches){
            global $CustomSearchFieldStatic;
            ob_start();

            $preset=$reMatches[1];
            if(!$preset) $preset = 'default';
            wp_custom_fields_search($preset);

            $form = ob_get_contents();
            ob_end_clean();
            return $form;
        }
    }
    global $CustomSearchFieldStatic;
    $CustomSearchFieldStatic['Inputs'] = array();
    $CustomSearchFieldStatic['Types'] = array();

    class AdminDropDown extends DropDownField {
        function AdminDropDown($name,$value,$options,$params=array()){
            AdminDropDown::__construct($name,$value,$options,$params);
        }
        function __construct($name,$value,$options,$params=array()){
            $params['options'] = $options;
            $params['id'] = $params['name'];
            parent::__construct($params);
            $this->name = $name;
            $this->value = $value;
        }
        function getHTMLName(){
            return $this->name;
        }
        function getValue(){
            return $this->value;
        }
        function getInput(){
            return parent::getInput($this->name,null);
        }
    }

if (!function_exists('json_encode'))
{
  function json_encode($a=false)
  {
    if (is_null($a)) return 'null';
    if ($a === false) return 'false';
    if ($a === true) return 'true';
    if (is_scalar($a))
    {
      if (is_float($a))
      {
        // Always use "." for floats.
        return floatval(str_replace(",", ".", strval($a)));
      }

      if (is_string($a))
      {
        static $jsonReplaces = array(array("\\", "/", "\n", "\t", "\r", "\b", "\f", '"'), array('\\\\', '\\/', '\\n', '\\t', '\\r', '\\b', '\\f', '\"'));
        return '"' . str_replace($jsonReplaces[0], $jsonReplaces[1], $a) . '"';
      }
      else
        return $a;
    }
    $isList = true;
    for ($i = 0, reset($a); $i < count($a); $i++, next($a))
    {
      if (key($a) !== $i)
      {
        $isList = false;
        break;
      }
    }
    $result = array();
    if ($isList)
    {
      foreach ($a as $v) $result[] = json_encode($v);
      return '[' . join(',', $result) . ']';
    }
    else
    {
      foreach ($a as $k => $v) $result[] = json_encode($k).':'.json_encode($v);
      return '{' . join(',', $result) . '}';
    }
  }
}
function wp_custom_fields_search($presetName='default'){
    global $CustomSearchFieldStatic;
    if(strpos($presetName,'preset-')!==0) $presetName="preset-$presetName";
    $CustomSearchFieldStatic['Object']->renderWidget(array('widget_id'=>$presetName,'noTitle'=>true),array('number'=>$presetName));
}
function compat_method_exists($class,$method){
    return method_exists($class,$method) || in_array(strtolower($method),get_class_methods($class));
}