如何以面向对象的方式处理一对多关系？

I'm building a database of artists, I would like to update/create the genres played by the artist in an object oriented way. I currently have 3 tables:

Table name:artists

I created a genres table which consists of 4 possible genres that artists can perform: Classical, Hiphop, Jazz and Other.

Table name: genres

Each artist has a one-to-many relationship with genres:

Table name: artist_genres

What I want is to output the genres played by the artist in the following form: $artist->genres will output all genres, for I'd have a function in the artist class like:

public static function find_genres_by_id($id=0){
  }

The above will only give me ids which I will need to look up in the genres table. The problem is that the above is not an array and I can't use it directly. However, I came up with the following code to do what I want:

global $database;
$sql = "SELECT genre_id FROM artists JOIN artist_genres ON artists.id=artist_genres.artist_id WHERE artist_id=8";
$answer = $database->query($sql);
while ($row = $answer->fetch_assoc()) {
$genresql = "SELECT genre_name FROM genres WHERE id=".$row['genre_id'];
$genrelist = $database->query($genresql);
while ($genrerow = $genrelist->fetch_assoc()){
  echo $genrerow['genre_name']."<br>";
}

This simply outputs the genres, but I want to be able to be able to instantiate and use a simpler echo $artist->genres to output the genres. I can currently do this for $artist->id , $artist->first_name etc. after using $artist=Artist::find_by_id($id)

EXTRA(I HAVE THE FOLLOWING FUNCTIONS):

class DatabaseObject {

  public static function find_available_artists() {
    return static::find_by_sql("SELECT * FROM artists WHERE availability=1");
  }
  public static function find_genres_by_id($id=0){
    return static::find_by_sql("SELECT genre_id FROM allartists JOIN artist_genres ON allartists.id=artist_genres.artist_id WHERE artist_id={$id}");
  }

  public static function find_all() {
    return static::find_by_sql("SELECT * FROM ".static::$table_name);
  }

  public static function find_by_id($id=0) {
    $result_array = static::find_by_sql("SELECT * FROM ".static::$table_name." WHERE id={$id} LIMIT 1");
    return !empty($result_array) ? array_shift($result_array) : false;
  }
   public static function find_by_sql($sql=""){

     global $database;
     $result_set = $database->query($sql);
     $object_array = array();
     while ($row = $database->fetch_array($result_set)) {
       $object_array[]=static::instantiate($row);
     }
     return $object_array;
   }


   private static function instantiate($record){
   $class_name = get_called_class();
   $object = new $class_name;

   foreach($record as $attribute=>$value) {
    if($object->has_attribute($attribute)) {
      $object->$attribute = $value;
    }

   }
   return $object;
   }
   private function has_attribute($attribute) {
     $object_vars = get_object_vars($this);
     return array_key_exists($attribute, $object_vars);

   }

Does your artist entity class have a "genres" field, an array, which you can add to?

<?php

class Artist 
{
    private $genres;

    public function addToGenres($genre)
    {
        $this->genres[] = $genre;
    }
}