[12.x] feat: add CanBeOneOfMany support to HasOneThrough

[calebdw]

Hello!

Closes #54720

This adds *OfMany support to the HasOneThrough relationship:

class Project extends Model
{
    public function latestDeployment(): HasOneThrough
    {
        return $this->deployments()->one()->latestOfMany(); // works!
    }

    public function deployments(): HasManyThrough
    {
        return $this->hasManyThrough(Deployment::class, Environment::class);
    }
}

Thanks!

[taylorotwell]

Why is this removed?

[calebdw]

It's not needed and adds double constraints:

For example, on existing relations:

On the HasOneThrough relation in particular it added a double join clause that prevented the query from even functioning.

[BertvanHoekelen]

The removal of this constraint causes all rows in the database to be loaded and than filtered while before the query was more narrow and only returned the required results. I have opened an issue for this, I can create a PR reverting this change but I don't know what the impact is on the feature that was added in this PR.

[calebdw]

@BertvanHoekelen, the constraints should have already been added by the time this was called (in the Relation constructor)---see the tests, this was adding double constraints.

I'll take a look, there must be a path where the constraints aren't added but we didn't have a test case for it

[taylorotwell]

Thanks!

[taylorotwell]

@calebdw would you mind PRing the docs for this?

[calebdw]

Sure thing!