Question

Somehow I can’t figure out how to implement the following relations
using Doctrine 2 syntax:

I have Items and Shops. Each item has different price and different
quantity at each shop. So, I have Items table, Shops table and
ItemsAtShops table. How do I reflect the last one in Doctrine?

I guess I need to create ItemsAtShops entity, relates ManyToOne ->
Items and ManyToOne -> Shops, right? But in this case… how do I
conveniently fetch a list of Items at the specific Shops with their
prices and quantities at given Shops? So, that all these can be
conveniently iterated?

I need to render a page with a list of Items and their Prices and
Quantities at specific shops. There is a template for displaying Item
there (with all it’s subproperties – prices etc). So, it would be the most convenient to pass just one object to
this template and iterate it and it’s subobjects (if any) there.

Answer 1

I struggle with this kind of scenario in Doctrine, as well. Rails had spoiled me with their has_many :through => relationship which makes this sort of thing trivial.

You are correct, you do need three entities: Shops, Items, ItemsAtShops using dual ManyToOne relationships.

I would assume that ItemsAtShop would look like:

class ItemsAtShop 
{        
   private $shop;
   private $items;
   private $quantity;
}

As far a querying goes, you’ll need to rock the joins:

$queryBulder->select('ias')
            ->from(ItemsAtShop, 'ias')
            ->leftJoin('ias.Item', 'i')
            ->leftJoin('ias.Shop', 's')
            ->where('s.id = :shop_id')
            ->andWhere('i.price <= :my_price')
            ->orderBy('i.price', 'DESC');

Remember, when using DQL, you’re usually querying entire Entity objects, which will fetch their relationships on their own. This should result in a collection of ItemsAtShop you can iterate over.

I might take some fidgeting to figure out the correct query. I’ll often start with a SQL query I know works, and translate it into DQL.