title: Meteor: Remove collection attributes when another collection is deleted
body: <p>I have two collections: one for Posts and one for Categories.  Posts have one or more categories. I'd like for the Posts collection to be updated if a category is deleted, so that posts do contain any non-existent categories. I've got this to work, but I'm not sure it is the most efficient way to do it. </p>
  
  <p>This code is what fires when a category delete button is pressed. This both removes the category from the collection, and goes through each post that contains the category and updates the category array to exclude the deleted category.</p>
  
  <pre><code>Template.listCategories.events({
      'click .delete-category': function(e){
          e.preventDefault();
          var category = this.name;
          Categories.remove(this._id);
  
          var posts = Posts.find({categories: category}).fetch();
          for (var i=0;i&lt;posts.length;i++){
              var cats = _.without(posts[i].categories, category);
              Posts.update(posts[i]._id, {$set: {categories: cats}});
          }       
      }
  });
  </code></pre>
  
  <p>First I set the a 'category' variable to equal the name of the category being deleted.
  Second, I actually remove the category from the collection.</p>
  
  <p>Lastly, I set a 'posts' variable equal to a fetch of all posts that contain the category name, which returns an object of posts. I iterate through the posts, and, with the help of underscore, I use the '_.without' function to return an array of categories that excludes the deleted category. I then call Posts.update to update the categories with the new array.</p>
  
  <p>My concern, though, is that I'm calling Posts.update each time in the For loop. It's a client side call, so maybe that doesn't matter as much? I still feel like there is a better way to do this. Any help?</p>