Showing the right records - php

Question

I am making a sort of forum for myself to see how everything works. Its build in PHP (PDO) and now I got the problem. I can't figure out how I make sure when someone clicks on a record out of the board that it will only show the items with the topic_id that is set to that board
This is the topic database
This is the boards database
The code too show the board(s):
<section class="col-md-8 connectedSortable">
<div class="box box-info">
<div class="panel panel-default">
<div class="panel-heading main-color-bg">
<h3 class="panel-title">Boards</h3>
</div>
<div class="panel-body">
<?php
$boardss = $app->get_boards();
foreach($boardss as $board){
echo '<div class="col-md-6">';
echo '<div class="well dash-box">';
echo '<h3>'.$board['topic'].'</h3><br>';
echo '' .$board['omschrijving'].'';
echo '</div>';
echo '</div>';
}
?>
</div>
</div>
</div><!-- /.box -->
</section><!-- right col -->
The functions I use:
public function get_boards(){
$getBoards = $this->database->query("SELECT * FROM boards ORDER BY id DESC");
$boards = $this->database->resultset();
return $boards;
}
public function get_topics(){
$getTopic = $this->database->query("
SELECT topics.*, klanten.foto, klanten.voornaam, klanten.achternaam FROM topics
LEFT JOIN klanten ON topics.klant_id=klanten.id
ORDER BY id ASC");
$topics = $this->database->resultset();
return $topics;
}

Answer 1

When generating the link to the board page, you need to specify which board is actually called. Your current code looks like this:
echo '' . $board['omschrijving'] . '
As you can see, the call itself, which is in the href attribute, does not contain any information. Instead, you should add the primary key of the board there:
echo '' . $board['omschrijving'].'
If that is done, you can get the current board on the boards page via $_GET:
$currentBoard = $_GET['board'];
if (!is_numeric($currentBoard)) {
die('Not a valid board id');
}
$currentBoard = (int)$currentBoard;
With that information, you can then can specify the topic for the board, by adding it to your query in get_topics() and adding the board is as parameter to the function. (get_topics($currentBoard))
SELECT
topics.*,
klanten.foto,
klanten.voornaam,
klanten.achternaam
FROM
topics
LEFT JOIN klanten ON topics.klant_id=klanten.id
WHERE
topics.board_id = :board
ORDER BY id ASC
That statement uses the parameter :board, which you can replace in a prepared statement with the variable $currentBoard. I would highly encourage you to use prepared statments in that case.

Answer 2

Add parameter $board_id to get_topics(), then add a WHERE clause for the passed $board_id, so that only topics of that board will be fetched.
Updated Function:
public function get_topics($board_id){
$getTopic = $this->database->query("
SELECT topics.*, klanten.foto, klanten.voornaam, klanten.achternaam FROM topics
LEFT JOIN klanten ON topics.klant_id=klanten.id
WHERE topics.board_id = '$board_id'
ORDER BY id ASC");
$topics = $this->database->resultset();
return $topics;
}