updated_at in custom pivot table works incorrectly

[dendev21]

• Laravel Version: 7.21.0
• PHP Version: 7.4.8
• Database Driver & Version: postgres:9.6

Description:

Defining UPDATED_AT as null in custom intermediate pivot table seems to be broken. $this->getUpdatedAtColumn() gets column name from parent model instead of custom pivot and as result it fails inserting to undefined column.
In version 5.8 column name was retrieved by static::UPDATED_AT and behaved right.

Illuminate\Database\Eloquent\Concerns\HasTimestamps:updateTimestamps()

protected function updateTimestamps()
{
    $time = $this->freshTimestamp();

    $updatedAtColumn = $this->getUpdatedAtColumn();

    if (! is_null($updatedAtColumn) && ! $this->isDirty($updatedAtColumn)) {
        $this->setUpdatedAt($time);
    }

    $createdAtColumn = $this->getCreatedAtColumn();

    if (! $this->exists && ! is_null($createdAtColumn) && ! $this->isDirty($createdAtColumn)) {
        $this->setCreatedAt($time);
    }
}

[driesvints]

I'm suspecting #30697 to be the culprit but trying to find out why this is breaking for you. Can you please paste your models/pivot and how you're using this exactly?

[dendev21]

I've created a demo project which shows how to reproduce the issue. You can see an exception executing php artisan demo:sync within app container

Illuminate\Database\QueryException 

SQLSTATE[42703]: Undefined column: 7 ERROR:  column "updated_at" of relation "post_has_comments" does not exist
LINE 1: update "post_has_comments" set "created_at" = $1, "updated_a...
                                                      ^ (SQL: update "post_has_comments" set "created_at" = 2020-09-27 19:46:15, "updated_at" = 2020-09-27 19:46:15 where "id" = 1)

Post model has relation to Comment model using PostHasComments pivot model.
Moreover table name in PostHasComments does not work at all. I had to add table name in comments relation

[driesvints]

After a long and deep dive into this I've determined that this has never worked, not even in 5.8. I tested with your code in a fresh 5.8 install and I get the same error. The Pivot always expects a created_at and updated_at column to be present and indeed derives their names from the parent model if not set explicitly. Their names are set on the pivot model through the pivotCreatedAt and pivotUpdatedAt properties rather than a UPDATED_AT constant. That's a bit of a bizar difference but it's the way it currently and afaik always has worked.

As this is sort of expected behavior (for now) I'm closing this. We can look into improving this but that's an enhancement rather. I'll send in a PR to the docs to document this. Thanks.

[driesvints]

PR for docs was merged: laravel/docs#6427