[5.7] Support MorphTo eager loading with selected columns

[staudenmeir]

When eager loading MorphTo relationships, you can't limit the selected columns (of course, these columns have to be available in all the related tables):

Comment::with('commentable:id,title')->get();

# expected
select "id", "title" from "posts" where "posts"."id" in (?)

# actual
select * from "posts" where "posts"."id" in (?)

As with withoutGlobalScopes() (#25331), we can use the $macroBuffer to fix this. We can also simplify the whole implementation.

Fixes #2966.

[sisve]

Removing the withoutGlobalScopes looks like a breaking change. Are you sure that methods needs to be removed? Should this target the 5.8 release instead?

[staudenmeir]

It doesn't have to be removed, but the new implementation is much shorter.

What would be a case where removing the method breaks existing code? If you override it, calling parent::withoutGlobalScopes() still works.

[sisve]

You're right, I was to quick to comment about these changes. Since the same behavior is kept in __call then my initial comment about breaking change was wrong.

[lk77]

Hello,

#25662 introduce a bug,
we have thousand of queries using the with 'relation:field' syntax with polymorphic relations,
and it's not working anymore, the relation is now empty.
i don't know why, but it dont happen in 5.7.5, only until 5.7.6

work :

->with('morphTo');

don't work :

->with('morphTo:label');

if you have an idea, thanks.

[staudenmeir]

@lk77 Please open a new issue and provide more details. How is the relationship defined? What does "don't work" mean?

[lk77]

@staudenmeir the relation is empty.
the relation is a very simple polymorphic relation,
using :

->morphTo('relation')

i would open an issue if i can replicate on fresh laravel install.

thanks.

edit: issue opened #26291