[jifty-devel] Re: Serious thought on relationships

[Andrew Sterling Hanenkamp]

Jesse,

After the foobar commit r3908, I've been digging deeper on the idea of
relationships and I have not yet been able to come up with a consistent
syntax for handling the more complex relationships I've suggested here
without breaking something.

If I assume that all refrences are based upon the ID column, it's no
problem, but having the ability (which I'm sure is nice) of creating
references with alternative columns becomes problematic because you have to
start worrying a lot more. Everything I think of is even more confusing.

Thus, I'm thinking of creating an index-relationship branch of JDBI that
would add superior index (multiple columns) and relationship (indexes that
link tables) handling to Jifty. This would be in addition to the
"references" syntax for specifying relatively simple relationships.

However, I don't know what has been done on this or thought about this
before. I was thinking that a Jifty::DBI::Index and Jifty::DBI::Relationship
class with additional declarations "index" and "relationsihp" to go along
side "column" would be nice, but I'm not sure what you were considering on
these fronts.

Cheers,
Andrew

On 8/15/07, Andrew Sterling Hanenkamp <sterling at hanenkamp.com> wrote:
>
> I spent much of today consider what can be done for relationships
> particularly after the discussion last month ("Regarding refers_to and by on
> JDBI columns"). I think I've got a plan for a number of handy updates
> relating to relationships.
>
> I'm already working on a patch to implement Idea 1. I think (at least the
> indirect record part) keeps things more consistent. The rest are sugar and
> I'll work to implement them too if everyone (particularly Jesse :) like B
> and III.
>
> Idea 1: Handling indirect relationships completely
>
> Currently, Jifty handles two types of relationships that I call "direct
> record" and "indirect collection".
>
> Direct Record: You can uses the C<references> keyword to create a column
> in one model referring to a record in another model.
>
> Indirect Collection: You can use the C<references> keyword with the C<by>
> keyword to create a virtual column that returns a collection of records such
> that the by column in the foreign records match the ID column of the current
> record.
>
> However, I think some effort will allow this to be expanded to handle two
> additional situations:
>
> Indirect Record: This would allow the C<references> keyword with the C<by>
> keyword to create a virtual column that returns a single record such that by
> column in the foreign record matches the ID column of the current record.
> This would allow you to traverse a one-to-one relationship in both
> directions. For example,
>
>   package App::Model::Employee;
>   use Jifty::DBI::Schema;
>   use App::Record schema {
>       column name => type is 'text';
>       column bio  => references App::Model::Bio, is distinct;
>   };
>
>   package App::Model::Bio;
>   use Jifty::DBI::Schema;
>   use App::Record schema {
>       column employee => references App::Model::Employee by 'bio';
>       column biography => type is 'text';
>   };
>
>
> Indirect Collection with Dereferencing: This adds a new keyword that would
> be used with C<reference> and C<by> called C<dereference>. Basically, the
> C<dereference> keyword would look up the the given column in the foreign
> model, which must be a reference to a record, and change the generated
> collection reference to return a collection for that record instead. This
> would allow you to have a many-to-many relationship with an invisible link
> table. For example,
>
>   package App::Model::Employee;
>   use Jifty::DBI::Schema;
>   use App:Record schema {
>       column name => type is 'text';
>       column supervisors => references App::Model::ManagerCollection
>                                     by 'supervisee',
>                            dereference 'supervisor';
>       column supervisees => references App::Model::ManagerCollection
>                                     by 'supervisor',
>                            dereference 'supervisee';
>   };
>
>   package App::Model::Manager;
>   use Jifty::DBI::Schema;
>   use App::Record schema {
>       column supervisor => references App::Model::Employee;
>       column supervisee => references App::Model::Employee;
>   };
>
> Idea B: Adding reverse mutators to indirect relationships
>
> The second step would be to add mutators to the indirect relationships
> allowing one to call backwards across a reverse relationship.
>
> For collections, this would include an add_to_* and a delete_from_*
> methods for creating and deleting records related to a collection.
>
> For records, this would include a set_* which would perform the set
> operation on the passed record object (or load the record from the passed ID
> and then set).
>
> Idea III: Adding the ability to create back-references in the originating
> file.
>
> Sometimes, it would be nice to be able to create the method calls to go
> from one direction to the other, but you don't have control over the foreign
> model. The specific possibility that could come up is in plugins, now that
> they can have their own models (blame me). It would be nice if the
> application could use tell Jifty to insert the back-reference methods in the
> other model.
>
> For example, here's a typical one-to-many relationship using the
> C<backreference> keyword as I imagine it:
>
>   package App::Model::Employee;
>   use Jifty::DBI::Schema;
>   use App::Record schema {
>       column name => type is 'text';
>   };
>
>   package App::Model::Address;
>   use Jifty::DBI::Schema;
>   use App::Record schema {
>       column employee => references App::Model::Employee,
>                       backreference 'addresses';
>       column name => type is 'text';
>       column address => type is 'text';
>   };
>
> With some help, similar logic could be applied to the indirect record and
> indirect collection with dereferencing examples above too.
>
> Cheers,
> Andrew
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.bestpractical.com/pipermail/jifty-devel/attachments/20070819/4d847a37/attachment.htm