How to post an current id - php

Question

I am making a forum, and I can add a reaction to save in the database, the only problem now is that it will leave empty id in the database.
The database:
How it will post it now:
Now I need to find a way to add the ledenpagina_id, topic_id and klant_id automatic. The klant_id needs to be set based on the klant session, but I am not sure how to get that.
The topic_id is set as active_id like this:
$actieftopicid = $topic['id'];`
But I don't know how to add that in the post so it will save it the correct way in the database.
I have tried doing this:
$q1['topic_id'] = $app->check_string($_POST[$topic['id']]);
But that isn't working.
The code to post it in the database:
<?php
if(isset($_POST['react_btn'])){
unset($q1);
$q1['reactie'] = $app->check_string($_POST['reactie']);
$q1['topic_id'] = $app->check_string($_POST[$topic['id']]);
$app->insert_query('reacties', $q1, 'id');
}
?>
<form action="" method="post">
<div class="form-group">
<label for="comment">Reactie:</label>
<textarea class="form-control" name="reactie" rows="3" id="comment"></textarea>
<button type="submit" name="react_btn" class="btn btn-primary">Plaats reactie</button>
</div>
</form>

Answer 1

You can add the id of the topic into the form like this:
<form action="" method="post">
<div class="form-group">
<label for="comment">Reactie:</label>
<textarea class="form-control" name="reactie" rows="3" id="comment"></textarea>
<input type="hidden" name="topicid" value="<?php echo $topic['id']; ?>">
<button type="submit" name="react_btn" class="btn btn-primary">Plaats reactie</button>
</div>
</form>
and then you can use it like $_POST['topicid'], since that is the name of the hidden input. Also, instead of
unset($q1);
you need to initialize $q1 properly:
$q1 = array();