I'm not quite sure I understood you right. Where are you going to use it?
relation()->
[{many_to_one, [forum]},{one_to_many, [forum]}].
Where do you need to use it?
May be it would be more easy to help you if you show some code
examples you're going to use in your application.
On 7/7/09, Hao Chi Kiang <[email protected]> wrote:
>
> 2009/7/7 Alexander Dergachev <[email protected]>
>>
>> Hi. If I got it right, then I don't see any problem :)
>>
>> As I understood the concept of subforums, any forum can have some
>> number of subforums, but is it really case one subforum may be placed
>> in more them one forum? Do we really need many-to-many relation?
>>
>> On 7/7/09, Takayoshi Kyou <[email protected]> wrote:
>> >
>> > Hi all,
>> >
>> > I am trying to make a forum application that every forum can have
>> > their
>> > child-forums. But I found it hard to represent these with erlydb.
>> >
>> > First I tried to use a self-referencing many-to-many relation:
>> >
>> > new (A) ->
>> > Post_data = yaws_api:parse_post(A),
>> > {value, {parent_forum_id, Parent_forum_id_str}, Other_fields} =
>> > lists:keytake(parent_forum_id, 1,
>> > %% convert every keys from string to atom
>> > [ {list_to_atom(K), V} || {K, V} <- Post_data ]),
>> > New_forum = forum:save(forum:new_with(Other_fields)),
>> > Parent_forum_id = list_to_integer(Parent_forum_id_str),
>> > %% A negative parent ID means it is an orphan.
>> > if Parent_forum_id > 0 ->
>> > forum:add_forum( forum:find_id(Parent_forum_id), New_forum );
>> > true ->
>> > ok
>> > end,
>> > {ewr, forum, index}.
>> >
>> >
>> > But this isn't work because the relation between parent and child is
>> > "two-way"
>> > that I can't detect who is the parent and who are the childern when I
>> > use
>> > forum:forums to access it.
>> >
>> > Any idea?
>> >
>> >
>> > Thanks
>> > >
>> >
>>
>>
>> --
>> With Best Regards,
>> Alexander Dergachev
>>
>> >
>
> Oh. Maybe I'm going the wrong way...
> Yes, this is only a one-to-many relations that one forum can have many
> sub-forums. Is it means I should define a "self-referencing one-to-many
> relation"?
>
> But maybe why I think of many-to-many first is that I felt unnatural to
> write a
> self-referencing one-to-many relation.
>
> If table1 have a one-to-many relation to table2, I would say:
>
> -module(table1).
> relations () -> {one_to_many, [table2]}.
>
> -module(table2).
> relations () -> {many_to_one, [table1]}.
>
> But it's strange to say:
> relations () -> [{one_to_many, [forum]}, {many_to_one, [forum]}].
>
> Or maybe I should just use a extra column called parent_forum_id? If I do
> so,
> will it going to be inconvenient to access them (because erlydb won't make
> access functions automatically)?
>
>
> Thanks.
>
> >
>
--
With Best Regards,
Alexander Dergachev
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