[wp-trac] [WordPress Trac] #14513: Time for a wp_post_relationships table?

[WordPress Trac]

#14513: Time for a wp_post_relationships table?
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 Reporter:  mikeschinkel     |        Owner:         
     Type:  feature request  |       Status:  closed 
 Priority:  normal           |    Milestone:         
Component:  Post Types       |      Version:  3.0.1  
 Severity:  normal           |   Resolution:  wontfix
 Keywords:                   |  
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Comment(by mikeschinkel):

 Replying to [comment:39 Denis-de-Bernardy]:
 > Replying to [comment:37 westi]:
 > > Sometimes you will need more than core to develop a complex site - we
 are not trying to solve 100% of use cases only the more significant ~80%.
 The other 20% is where plugins sit in the eco-system so that you can make
 it your WordPress
 >
 > Best I'm aware, situations where node2node relationships are desirable
 include the vast majority of non-trivial/real-life business applications.
 The keyword here is business: people who pay to get a website that is of
 any use to them, as opposed to a corporate blog for PR purposes.

 Exactly.

 I wasn't going to continue, but since Denis did... I'd argue that (what in
 WordPress would be) post-to-post relationships are in the 90th percentile
 case; certainly not in the 20th percentile.  If we accept the custom post
 types are WordPress' equivalent of a "relation" (relations are viewed as
 "tables"[1]) in the relational model for "large shared data banks" as
 written about by E. F. Codd in 1970[2] then this pattern is one of the
 most fundamental pattern in relational databases that exist.

 The "post-to-post" relationship would be implemented simply with a table
 that allows the creation of a many-to-many connection to store as foreign
 keys[5] the primary keys[6] of posts, in our case $post->ID. This concept
 is fundamental to every relational database system ever built, not some
 "''edge''" use case.

 Because of it's origins WordPress has nailed the blogging pattern and with
 that pattern has implemented many primary key to foreign key
 relationships:

  * $post->post_parent TO $post->ID
  * $term_relationships->object_id TO $post->ID
  * $comment->comment_post_ID TO $post->ID
  * $postmeta->post_id TO $post->ID
  * And several more.

 Given WordPress implements the blogging pattern so well maybe it's not
 clear that the missing fundamental component required for implementing
 generic database-oriented business systems for arbitrary business use-
 cases is the post-to-post table aka the many-to-many[7] table.
 Alternately we could build out each new use-case pattern for which people
 want to use WordPress for much like the blogging use-case pattern was
 built out but why go that route (aside from it will never happen) when we
 can simply include the low-level many-to-many functionality and let people
 build it themselves?

 So this is not a stretch nor some obscure need. This is as low a level of
 fundamental building block as you can get it WordPress and it's the last
 major one that's missing.

  * [1]
 http://en.wikipedia.org/wiki/Relational_model#Relational_model_topics
  * [2] http://www.seas.upenn.edu/~zives/03f/cis550/codd.pdf
  * [3] http://en.wikipedia.org/wiki/Relational_model#Examples
  * [4] http://en.wikipedia.org/wiki/Many-to-many_(data_model)
  * [5] http://en.wikipedia.org/wiki/Foreign_key
  * [6] http://en.wikipedia.org/wiki/Primary_key
  * [7] http://en.wikipedia.org/wiki/Many-to-many_(data_model)

 > One of the more compelling examples Mike gave, IMO, was the one for the
 law firm. The little I've worked in that field would have had me laugh at
 the idea of using WP. You ''can'' bend reality to make things fit in
 taxonomies and meta tables, in order to fit real life situations into an
 arbitrary schema. But for such a setup you quickly end up ditching WP
 altogether, in favor of Drupal (barely better) or a php framework.

 LOL! Denis, PLEASE don't tell my client that! :-) :-) :-)  I told them
 that WordPress would be better than Drupal or a PHP framework and they are
 paying me by the hour to spend hundreds of hours building on that use-
 case! (I'm hoping that I'm not proven wrong here.)

 FWIW I'm basically building a law firm website plugin that can be used to
 launch hundreds if not thousands of law firm websites which is the
 business my client is in; managing websites for larger law firms. My code
 will be replacing their former custom content management system.

 And guess what? I'm developing some potentially really significant
 functionality I will be launching as plugins where the functionality is
 targeted at developers and themers not at end users. Said another way,
 because the company is paying me to build a business system on top of
 WordPress (a business system which needs robust post-to-post
 relationships, as almost all business systems built on WordPress will
 need) I am able to spend lots of time building functionality I can
 contribute to the community. (You've probably seen my recent helping of
 people on the wp-hackers list; that knowledge came from being commissioned
 to delve deep into WordPress and learn it's low-level functionality. Later
 contributions will be plugins after I can package and document them.)

 But this isn't about me and my development; maybe my stuff is all crap;
 who knows? It's about all the other developers who could be commissioned
 to build business systems too. And because they would get to focus their
 time on developing for interesting business use-cases some of them would
 develop generic tool sets and contribute them back to the community thus
 growing the use-cases that WordPress can be used for with trivial effort.

 But if the only use-case pattern WordPress addresses well is the blogging
 pattern then the majority of interesting generic toolsets that will be
 contributed back will continue to be by and large for blogging (I'm not
 saying WordPress can't currently address those interesting use-cases, it
 would just be a lot easier if there were a standard way to relate posts to
 posts.)

 There are numerous ways to address this need without requiring the
 relationships be more complex than a single linking table; I'm just asking
 for one of them:

  * Add a `wp_post_relationships` table
  * Add a "`parent_post`" field to `wp_postmeta`
  * Overload `wp_term_relationships` by adding a "`post_id`" field.
  * And I am sure there are other ways to tackle this too.

 FWIW.

 -Mike

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Ticket URL: <http://core.trac.wordpress.org/ticket/14513#comment:40>
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