[Dbix-class] Relationship::Base join-free exception question

[Peter Rabbitson]

On 07/06/2015 02:44 AM, Marco Palma wrote:
> Hey all, I'm hoping someone can clarify for me an exception that get's
> thrown in Relationship::Base. I'm have multipurpose comments table that
> could be used for commenting on different kinds of objects in a schema.
>   Rather than having individual join-tables to cement the relationships,
> I want to using a compound foreign key of object_type + object_id.
>
> ...
> Which comes from the *new_related* method:
>
>      $self->throw_exception("Custom relationship '$rel' does not resolve
> to a join-free condition fragment")
>        if $crosstable;
>
> If I comment that check out, I can use the above has_many without issue.

Actually this is not exactly the case. Your "new related" object does 
not have any of its FKs set to values coming from the "left-side" object.

> So I'm curious:
>
>    - What is that exception meant to overcome?
>    - Why must my relationship resolve to a "join-free" condition?
>

Before we go further - have you carefully read 
https://metacpan.org/pod/DBIx::Class::Relationship::Base#Custom-join-conditions, 
especially the paragraph starting with "While every coderef-based 
condition must return..."

If after (re)reading this you are still unsure what this is all about - 
don't hesitate to ask.

Cheers!