How to write exists subquery DQL for many to many association - doctrine-orm

Question

Given the entities below, would someone please help me understand how to write the DQL equivalent of the following SQL? I can't seem to find a good example of a DQL subquery that translates to a select on a pivot table. Thank you!
select *
from event a
where exists (
select *
from event_category b
where b.event_id = a.id
and b.category_id = 1
)
Entities:
/**
* #Entity
* #Table(name="event")
*/
class Event
{
/**
* #Column(type="integer")
* #Id
*/
protected $id;
/**
* #JoinTable(
* inverseJoinColumns={
* #JoinColumn(name="category_id", referencedColumnName="id")
* },
* joinColumns={
* #JoinColumn(name="event_id", referencedColumnName="id")
* },
* name="event_category"
* )
* #ManyToMany(targetEntity="Category")
*/
protected $categories;
}
/**
* #Entity
* #Table(name="category")
*/
class Category
{
/**
* #Column(type="integer")
* #Id
*/
protected $id;
}

Answer 1

Please have a look at Doctrine Query Language
Your example could be written :
SELECT event FROM Event event
WHERE EXISTS (
SELECT cat FROM Category cat
WHERE IDENTITY(cat.event) = event.id
AND cat.id = 1
)
Now I might be wrong but I don't think you need a subquery here.
If you want events that have a given category :
SELECT event FROM Event event JOIN event.category WHERE category.id = 1