Checkboxes and setting their default checked values from the database

Question

I have the following database table called artist_genres. I currently have a function which finds all genre_id's by artist and echo's them in an object oriented way:

<?php
$artistgenres = Artistgenres::find_all_genres_by_artist_id($_SESSION['artist_id']);
foreach($artistgenres as $artistgenre){
  echo $artistgenre->genre_id."<br>";
}
?>

When the artist with id 8 logs in, and goes to this page, I would like for him to be able to update the current genre_ids associated with them.

The form data looks like:

<form action="<?php echo $_SERVER['PHP_SELF'];?>" method="post">
<div class="checkbox">
  <label><input type="checkbox" name="Genres[]" value="2">Classical</label>
</div>
<div class="checkbox">
  <label><input type="checkbox" name="Genres[]" value="3">Hiphop</label>
</div>
<div class="checkbox">
  <label><input type="checkbox" name="Genres[]" value="4">Jazz</label>
</div>
<input type="submit" name="submit" class="btn btn-primary btn-lg active" id="grad" value="Login" />
</form> 

So effectively, for the classical example, what I want to achieve is to look up and find all genre_id, see if the value 2 is in the list of genre_ids, if so change the markup to:

  <label><input type="checkbox" name="Genres[]" value="2"<? php if(somecondition = 2) {echo "checked"} ?> >Classical</label>

However, I'm having a hard time putting this into code. Can you help me out?

Answer 1

Put all of the selected genres of the user in an array:

$selectedgenres = array();
foreach($artistgenres as $artistgenre){
    $selectedgenres[] = $artistgenre->genre_id;
}

List all genres as checkboxes (I assume you have a separate table for all of your genres). Then use in_array() to check each genre if it is part of the selected genres by the user:

foreach(your condition here for getting all genres){

?>    
    <div class="checkbox">
        <label><input type="checkbox" name="Genres[]" value="<?=($genreid)?>"><?=($genredesc)? <?php echo (in_array($genreid, $selectedgenres))?' checked':''; ?>></label>
    </div>

<?php

}