title: Accessing the join table in a hql query for a many-to-many relationship in grails
body: <p>I have 2 domain classes with a many-to-many relationship in grails: decks and cards.</p>
  
  <p>The setup looks like this:</p>
  
  <pre><code>class Deck {
  static hasMany = [cards: Card]
  }
  
  class Card {
  static hasMany = [decks: Deck]
  static belongsTo = Deck
  }
  </code></pre>
  
  <p>After I delete a deck, I want to also delete all cards which no longer belong to a deck. The easiest way to accomplish this is to write something like the following sql:</p>
  
  <pre><code>delete from card where card.id not in(select card_id from deck_cards);
  </code></pre>
  
  <p>However, I can't figure out how to write a HQL query which will resolve to this SQL because the join table, deck_cards, does not have a corresponding grails domain class. I can't write this statement using normal joins because HQL doesn't let you use joins in delete statements, and if I use a subquery to get around this restriction mySQL complains because you're not allowed to refer to the table you're deleting from in the "from" section of the subquery.</p>
  
  <p>I also tried using the hibernate "delete-orphan" cascade option but that results in all cards being deleted when a deck is deleted even if those cards also belong to other decks. I'm going crazy - this seems like it should be a simple task.</p>
  
  <p><em>edit</em> 
  There seems to be some confusion about this specific use of "decks" and "cards". In this application, the "cards" are flashcards and there can be tens of thousands of them in a deck. Also, it is sometimes necessary to make a copy of a deck so that users can edit it as they see fit. In this scenario, rather than copying all the cards over, the new deck will just reference the same cards as the old deck, and if a card is changed only then will a new card be created. Also, while I can do this delete in a loop in groovy, it will be very slow and resource-intensive since it will generate tens of thousands of sql delete statements rather than just 1 (using the above sql). Is there no way to access a property of the join table in HQL?</p>