symfony - How can make a INNER JOIN in a DQL sentence? -

i have problem dql in symfony2 project. have defined 3 entities:

• a entity called category 2 fields : id , slug
• a entity called subcategory 2 fields : id , slug
• a entity called categorysubcategories 2 fields : category , subcategory

i need obtain subcatgories category (slug) given. got next dql :

$em ->createquery('select subcat subcategory subcat subcat.id in                                         (select identity(csc.subcategory)  categorysubcategories csc csc.category in (select cat category cat cat.slug = :category))')                     ->setparameter('category', $category); 

is there anyway build dql inner joins ?

in mysql example:

select subcat.slug category cat inner join categorysubcategories csc on (cat.id = csc.category_id) inner join subcategory subcat on (csc.subcategory_id = subcat.id) cat.slug "$category"

is there anyway translate dql ?

in own opinion, there no need have third entity, 2 enough (category , subcategory) , add association manytoone between subcategory , category, described here: http://docs.doctrine-project.org/en/2.1/reference/association-mapping.html