How to let Laravel pivot table use only created_at?

When dealing with belongsToMany relation, you use a pivot table to record the relation.

For many pivot tables, the relations are just created and then deleted. They won't have their own property, so you never update them.

I know I can do this to auto-set both updated_at and created_at.

class Foo extends Model
{
    public function bars() {
        $this->belongsToMany(Bar::class)->withTimestamps();
    }
}

But how to use only created_at? I have no idea.

via Chebli Mohamed