How to join a many to many relationship - mysql

Question

Entities :
Model
Category
Keyword
Model has a many to many relationship to keyword as well as category has a many to many relationship to keyword.
The orm generates following tables
model
category
keyword
keyword_model
keyword_category
When a category is given, how can I get all models related to this category? I would do it like this
get all keyword id's from keyword_category by category.id
join the result with the keyword_model table
the result of the join should be all relevant model id's
Since symfony2 deals with entities and not tables it seems hard to create a mysql query. I tried with something like
SELECT x,y FROM MyBundle:Category x, MyBundle:Model y
JOIN x.keywords
JOIN y.keywords
WHERE
x.id = " . $category . "
however this is invalid mysql syntax. Any ideas how to get the models here?

Answer 1

You could try the following:
SELECT
y
FROM
MyBundle:Model y
WHERE
EXISTS (
SELECT
x
FROM
MyBundle:Category x
JOIN
x.keywords xk
WHERE
xk MEMBER OF y.keywords AND
x = :category
)
Or if your relations are bidirectional:
SELECT
y
FROM
MyBundle:Model y
JOIN
y.keywords yk
JOIN
yk.categories c
WHERE
c = :category

Answer 2

From a given category (I suppose that you have the id)
$category_repo = $this->getDoctrine()->getManager()->getRepository('YourBundleName:Category');
$category = $category_repo->findOneById($id); //$id is your entity id
$keywords = $category->getKeywords(); //getKeywords() is the name of the method that you should have inside your class
$models = new ArrayCollection(); //or use a simple array
foreach($keywords as $keyword) {
foreach($keyword->getModels() as $model) {
$models->add($model);
}
}
however use sql directly should be more performing as you'll do a single query instead of a query (lazy-loading concept) for each object