[RESOLVED] Extending class parent resets variable

adw999

What I am trying to do is build one parent class that then calls subclasses to query a database for a search term. I can get this to work with one subclass (SearchNews) but when trying to call a second child class (SearchProjects) all the variables are reset and only the Projects results are returned.

The calling code is:

$Search = new Search($keywords);
$News = new SearchNews($keywords);
$Projects = new SearchProjects($keywords);
$News->getResults();
$Projects->getResults();
$Search->writeResults();

And the Search classes are:

<?php
//Full text searching on news, projects and pages

class Search {
	protected $totalResults, $results, $keywords;

function __construct($keywords) {
	$this->keywords = $keywords;
	$this->totalResults = 0;
	$this->results = array();
}

protected function addResults($results) {
	$this->results = $this->results+$results;
}

protected function setResults($toAdd) {
	$this->totalResults = $this->totalResults+$toAdd;
}

protected function returnTotal() {
	return $this->totalResults;
}

protected function sortResults() {
	asort($this->results, SORT_NUMERIC);
}

public function writeResults() {
	$this->sortResults();
	$this->return = "<p>The search keywords '<em>".$this->keywords."</em>' returned ".$this->returnTotal()." results.</p>";
	$this->return .= "<table class=\"searchTable\">";
	$this->return .=  "<tr><th width=\"250\">Title</th><th>Body</th><th width=\"100px\">Relevance</th><th width=\"100px\">Area</th></tr>";
	foreach($this->results as $res) {
		$this->return .=  "<tr>";
		$this->return .=  "<td><a href=\"".$res['URL']."\">".$res['Title']."</a></td>";
		$this->return .=  "<td>".cleanOutput($res['Copy'])."</td>";
		$this->return .=  "<td align=\"center\">".$res['Score']."</td>";
		$this->return .=  "<td align=\"center\">".$res['Area']."</td>";
		$this->return .=  "</tr>";
	}
	$this->return .=  "</table>";
	return $this->return;		
}
}

class SearchNews extends Search {
	function __construct($keywords) {
		parent::__construct($keywords);
	}

public function getResults() {
	$query = "SELECT `Title`, `ID`, `Intro`, MATCH(`Title`, `Copy`, `Intro`) AGAINST ('".$this->keywords."' IN BOOLEAN MODE) AS `Score` FROM tblnews WHERE MATCH(`Title`, `Copy`, `Intro`) AGAINST ('".$this->keywords."' IN BOOLEAN MODE) ORDER BY `Score` DESC LIMIT 10";
	$results = mysql_query($query) or die("Cannot perform news search: ".mysql_error()."<br />".$query);
	$tr = parent::setResults(mysql_num_rows($results));
	if(mysql_num_rows($results) > 0) 
		while($res = mysql_fetch_array($results))
			$this->results[] = array('Score'=>(round($res['Score'], 3)*100), 'Title'=>$res['Title'], 'Copy'=>firstParagragh($res['Intro']), 'URL'=>'/news/'.$res['ID'].'/', 'Area'=>'News');
}	
}

class SearchProjects extends Search {
	function __construct($keywords) {
		parent::__construct($keywords);
	}

public function getResults() {
	$query = "SELECT `Title`, `ProjectID`, `Copy`, MATCH(`Title`, `Copy`) AGAINST ('".$this->keywords."' IN BOOLEAN MODE) AS `Score` FROM tblprojects WHERE MATCH(`Title`, `Copy`) AGAINST ('".$this->keywords."' IN BOOLEAN MODE) ORDER BY `Score` DESC LIMIT 10";
	$results = mysql_query($query) or die("Cannot perform news search: ".mysql_error()."<br />".$query);
	$tr = parent::setResults(mysql_num_rows($results));
	if(mysql_num_rows($results) > 0) 
		while($res = mysql_fetch_array($results))
			$this->results[] = array('Score'=>(round($res['Score'], 3)*100), 'Title'=>$res['Title'], 'Copy'=>firstParagragh($res['Copy']), 'URL'=>'/projects/'.$res['ProjectID'].'/', 'Area'=>'Projects');
}	
}

?>

I thought using $this->results[] would add to the parent variable but im guessing the parent constructor is resetting the variables when the second child class is called. How do i get around this (keep existing variable data)?

thanks

laserlight

adw999 wrote:
I can get this to work with one subclass (SearchNews) but when trying to call a second child class (SearchProjects) all the variables are reset and only the Projects results are returned.

That's weird. You are using non-static member variables, so I would expect that no results are returned.

I think that inheritance is not quite the correct solution here. What you have is a some kind of "result aggregator" (i.e., an object that collects all the results into a total, and with which you print the aggregated results), and then a bunch of "result retrievers" (i.e., objects that retrieve the desired results from the corresponding sources). If you want to use inheritance, it should be for a hierarchy of result retrievers.

For example:

interface ResultRetriever {
    function getResults($keywords);
}

class ResultAggregate {
    private $results;
    private $keywords;
    private $result_retrievers;

function __construct($keywords) {
    $this->results = array();
    $this->keywords = $keywords;
    $this->result_retrievers = array();
}

function add(ResultRetriever $result_retriever) {
    $this->result_retrievers[] = $result_retriever;
}

function process() {
    foreach ($result_retrievers as $result_retriever) {
        $this->results[] = $result_retriever->getResults($this->keywords);
    }
}

function writeResults() {
    // ...
}
}

class SearchNews implements ResultRetriever {
    function getResults($keywords) {
        $results = array();
        // ... use $keywords in the SQL statement ...
        return $results;
    }
}

class SearchProjects implements ResultRetriever {
    function getResults($keywords) {
        $results = array();
        // ... use $keywords in the SQL statement ...
        return $results;
    }
}

// ...

$result_aggregate = new ResultAggregate($keywords);
$result_aggregate->add(new SearchNews());
$result_aggregate->add(new SearchProjects());
$result->aggregate->process();
$result->aggregate->writeResults();

The ResultRetriever hierarchy could be eliminated by making it such that you change the SQL statement and some other attributes in order to retrieve and format different results.

adw999

thanks for the reply/code. I'm very open to ideas - what would be the best way to do it?

I need different functions to get different areas as sometimes an area might not be needed (ie. i want projects, not news).

laserlight

adw999 wrote:
I'm very open to ideas - what would be the best way to do it?

For something similiar to what you were trying to do, I'd say that the approach I suggested is "best". It is basically an instance of the strategy design pattern. However, simplification seems feasible considering how similiar your getResult() functions for SearchNews and SearchProjects are.

adw999 wrote:
I need different functions to get different areas as sometimes an area might not be needed (ie. i want projects, not news).

You just add the ResultRetriever objects that you need to the ResultAggregate.

adw999

ok thanks very much

laserlight

No problem 🙂
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