How to get only name of parent and childrens? - php

Question

I have relations Article + Comment.
This:
$queryBuilder = $em->createQueryBuilder();
$queryBuilder->select('a, c')
->from(Article::class, 'a')
->leftJoin('a.comments', 'p');
$articles = $queryBuilder->getQuery()->getResult();
works correctly, but I would like less data, so I am trying:
$queryBuilder = $em->createQueryBuilder();
$queryBuilder->select('a.name, c')
->from(Article::class, 'a')
->leftJoin('a.comments', 'p');
$articles = $queryBuilder->getQuery()->getResult();
and I have error:
[Semantical Error] line 0, col -1 near 'SELECT a.name,': Error: Cannot select entity through identification variables without choosing at least one root entity alias.
If I use:
$queryBuilder->select('a.name, c.title')
then I have categories with key 'title' from first comment of article.
If I use:
$queryBuilder->select('a.name, a.comments')
then I have error:
[Semantical Error] line 0, col 15 near 'comments FROM': Error: Invalid PathExpression. Must be a StateFieldPathExpression.

Answer 1

If your relation is set proper, you could get your comments by calling this command:
$article->getComments();

Answer 2

In your left join, you are aliasing comments to 'p', but you are trying to access the comments with 'c' in your select. If you ->leftJoin('a.comments', 'c') then you should be able to access 'c.title' in your select. If this does not work you may need to check that your doctrine relations are set up properly in your entitites.

Answer 3

Indeed, if you want to retain object-oriented data access, you need to have a root element (in your case Article) which is used to traverse to other objects in your structure. In your case, this is simple - you only have a Comment (that we know of)
So, if you want to load less data you either:
Switch to array loading getArrayResult() instead of getResult(). With that, you are free to choose which fields are being loaded, but your lose objects. Everything you do, you will have to do it via array traversal. Example:
echo $article['comments'][0]['title'];
Alternatively, you can choose to load PARTIAL objects. Pros are that you retain object access, but cons are that you need to alter your SQL a bit. For example:
$queryBuilder->select('PARTIAL a.{name}', 'c')
->from(Article::class, 'a')
->leftJoin('a.comments', 'c');
$data = $queryBuilder->getQuery()->getResult();
Be aware that non-loaded fields are set to NULL so that may lead to unexpected attempts to dereference nulls.
Hope this helps...