Reduce DB query number in post index action

[yceruto]

Performance Issue

After tags feature the blog index page performs one extra query for each post to fetches its related tags. This PR avoids that.

Other changes:

• Refactoring the Post repository methods to reuse paginator creation in the future.

[javiereguiluz]

👍

Nice catch of this issue about the number of database queries! Thanks!

[Grafikart]

I noticed this issue too but I'm not sure avout this fix since the LIMIT is then applied to the tags. If the first post has 10 tags, then it will be the only one in the listing right ?

Doctrine doesn't seem to work well in this case. My solution for this kind of issues is to hydrate manually the entities using a new query on the joinTable.

[javiereguiluz]

@Grafikart I'm not sure I understand your comment. This is how join queries are supposed to work in Doctrine. I always use a code similar to this one. I've just tested this PR locally and it seems to be working as expected. The results are the same, but the database queries:

Before	After

[javiereguiluz]

Thanks Yonel.

[Grafikart]

@javiereguiluz sorry it works with PagerFanta indeed. It didn't worked for me cause I tried this PR without the paginator :

        $query = $this->getEntityManager()
            ->createQuery('
                SELECT p, t
                FROM AppBundle:Post p
                LEFT JOIN p.tags t
                WHERE p.publishedAt <= :now
                ORDER BY p.publishedAt DESC
            ')
            ->setMaxResults(5)
            ->setParameter('now', new \DateTime())

But doing a first query to get the posts ids (like PagerFanta does) solve this issue. Sorry for the false issue.