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Embracing Simplicity to Kill Conditional Complexity – A Real World Example

In the Agile India Submission system, we had a feature which would accept different url path to show matching proposals.

For example:
http://present.agileindia.org/agile-india-2014/agile-lifecycle/45_mins –> will return all 45 mins proposals under the Agile-Lifecycle track for the Agile India 2014 Conference.
http://present.agileindia.org/agile-india-2014/beyond-agile/90_mins –> will return all 90 mins proposals under the Beyond-Agile track for the Agile India 2014 Conference.

If we remove the last part .i.e. http://present.agileindia.org/agile-india-2014/agile-lifecycle –> will return all proposals under the Agile-Lifecycle track for the Agile India 2014 Conference.
and http://present.agileindia.org/agile-india-2014 –> will return all proposals for the Agile India 2014 Conference (could be other conferences as well.)

To achieve this, we had the following routes defined:

//URL Path = /agile-india-2014
app\get("/{conference}", function($req) {
    $query_params = structure_request_params($req['matches']);
    ...
});
 
//URL Path = /agile-india-2014/agile-lifecycle
app\get("/{conference}/{track}", function($req) {
    $query_params = structure_request_params($req['matches']);
    ...
});
 
//URL Path = /agile-india-2014/agile-lifecycle/45_mins
app\get("/{conference}/{track}/{label}", function($req) {
    $query_params = structure_request_params($req['matches']);
    ...
});

In our database we had the following:

CREATE TABLE `conference` (
  `key` VARCHAR(255) NOT NULL,
   ...
  PRIMARY KEY  (`key`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 
CREATE TABLE `track` (
  `conference` VARCHAR(255) NOT NULL,
  `key` VARCHAR(255) NOT NULL,
  ...
  PRIMARY KEY  (`key`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;  
 
CREATE TABLE `label` (
  `conference` VARCHAR(255) NOT NULL,
  `track` VARCHAR(255) NOT NULL,
  `key` VARCHAR(255) NOT NULL,
  ...
  PRIMARY KEY  (`conference`,`track`,`key`)
) ENGINE= InnoDB DEFAULT CHARSET=utf8;
 
INSERT INTO `conference` VALUES ('agile-india-2014', ...);
INSERT INTO `track` VALUES ('agile-india-2014', 'agile-lifecycle', ...);
INSERT INTO `label` VALUES ('agile-india-2014', 'agile-lifecycle', '45_mins', ...);

And some really complicated logic:

// For example URL Path /agile-india-2014 will result in 
// $req_params = array('conference'=>'agile-india-2014')
// And URL Path /agile-india-2014/agile-lifecycle will result in 
// $req_params = array('conference'=>'agile-india-2014', 'track'=>'agile-lifecycle')
// And URL Path /agile-india-2014/agile-lifecycle/45_mins will result in 
// $req_params = array('conference'=>'agile-india-2014', 'track'=>'agile-lifecycle', 'label'=>'45_mins')
function structure_request_params($req_params){
    $query_params = array();
    if(isset($req_params['label'])){
        if(Conference::exists($req_params['conference'])){
            $query_params['conference'] = $req_params['conference'];
            if(Track::exists(array('conference' => $req_params['conference'], 'key' => $req_params['track']))){
                $query_params['track'] = $req_params['track'];
                if(Label::exists(array(
                                       'conference' => $req_params['conference'], 
                                       'track' => $req_params['track'], 
                                       'key' => $req_params['label'])
                                       )) {
                    $query_params['label'] = $req_params['label'];
                }
                else{
                    $query_params['search_term'] = array($req_params['label']);
                }
            }
            else{
                $query_params['search_term'] = array($req_params['track'], $req_params['label']);
            }
        }
        else{
            $query_params['search_term'] = array($req_params['conference'], $req_params['track'], $req_params['label']);
        }
    }
    else{
        if(isset($req_params['track'])){
            if(Conference::exists($req_params['conference'])){
                $query_params['conference'] = $req_params['conference'];
                if(Track::exists(array('conference' => $req_params['conference'], 'key' => $req_params['track']))){
                    $query_params['track'] = $req_params['track'];
                }
                else{
                    $query_params['search_term'] = array($req_params['track']);
                }
            }
            else{
                if(Track::exists(array('key' => $req_params['conference']))){
                    $query_params['track'] = $req_params['conference'];
                    if(Label::exists(array('track' => $req_params['conference'], 'key' => $req_params['track']))){
                        $query_params['label'] = $req_params['track'];
                    }
                    else{
                        $query_params['search_term'] = array($req_params['track']);
                    }
                }
                else{
                    $query_params['search_term'] = array($req_params['conference'], $req_params['track']);
                }
            }
        }
        else{
            if(isset($req_params['conference'])){
                if(Conference::exists($req_params['conference'])){
                    $query_params['conference'] = $req_params['conference'];
                }
                elseif(Track::exists(array('key' => $req_params['conference']))){
                    $query_params['track'] = $req_params['conference'];
                }
                elseif(Label::exists(array('key' => $req_params['conference']))){
                    $query_params['label'] = $req_params['conference'];
                }
                else{
                    $query_params['search_term'] = array($req_params['conference']);
                }
            }
        }
    }
    return $query_params;
}

And supporting model classes:

class Conference{
    static function exists($conference){
        DB::query('SELECT * FROM conference WHERE conference.key = %s', $conference);
        return (DB::count() > 0);
    }
}
 
class Track{
    static function exists($query_params){
        $search_query = Track::create_search_query($query_params);
        DB::query("SELECT * FROM track WHERE $search_query");
        return (DB::count() > 0);
    } 
 
	private static function create_search_query($query_params){
        $search_query = array();
        foreach($query_params as $key => $value){
            $search_query[] = "$key='$value'";
        }
        return join(' AND ', $search_query);
    }
}
 
class Label{
    static function exists($query_params){
        $search_query = Label::create_search_query($query_params);
        DB::query("SELECT * FROM label WHERE $search_query");
        return (DB::count() > 0);
    }
 
	private static function create_search_query($query_params){
        $search_query = array();
        if(!empty($query_params)){
            foreach($query_params as $key => $value){
                $search_query[] = "$key='$value'";
            }
            return join(' AND ', $search_query);
        }
        return '';
    }
}

This was extremely hard to understand, so I decided to clean it up and get rid of the conditional complexity code smell.

Refactored code:

function structure_request_params($req_params){
    $criteria = array('conference', 'track', 'label');
    $params = array_values($req_params);
    return build_search_query_params($criteria, $params, array());
}
 
function build_search_query_params($criteria, $params, $results) {
    if(empty($params)) return $results;
    if(empty($criteria)) {
        if(!empty($params)) {
            $results['search_term'] = $params;
        }
        return $results;
    }
    if(is_present_in_db($criteria[0], $params[0])) {
        $results[$criteria[0]] = $params[0];
        array_shift($params);
    }
    array_shift($criteria);
    return map_criteria_params($criteria, $params, $results);
}
 
function is_present_in_db($table_name, $value){
    return (DB::queryFirstField("SELECT count(*) FROM $table_name WHERE `key` = %s", $value) > 0);
}

Also with this, we were able to delete the Model classes as they were not required.


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