Method for defining simultaneous has-many and has-one associations between two models in CakePHP?
- by Hobonium
One thing with which I have long had problems, within the CakePHP framework, is defining simultaneous hasOne and hasMany relationships between two models. For example:
BlogEntry hasMany Comment
BlogEntry hasOne MostRecentComment (where MostRecentComment is the Comment with the most recent created field)
Defining these relationships in the BlogEntry model properties is problematic. CakePHP's ORM implements a has-one relationship as an INNER JOIN, so as soon as there is more than one Comment, BlogEntry::find('all') calls return multiple results per BlogEntry.
I've worked around these situations in the past in a few ways:
Using a model callback (or, sometimes, even in the controller or view!), I've simulated a MostRecentComment with:
$this->data['MostRecentComment'] = $this->data['Comment'][0];
This gets ugly fast if, say, I need to order the Comments any way other than by Comment.created. It also doesn't Cake's in-built pagination features to sort by MostRecentComment fields (e.g. sort BlogEntry results reverse-chronologically by MostRecentComment.created.
Maintaining an additional foreign key, BlogEntry.most_recent_comment_id. This is annoying to maintain, and breaks Cake's ORM: the implication is BlogEntry belongsTo MostRecentComment. It works, but just looks...wrong.
These solutions left much to be desired, so I sat down with this problem the other day, and worked on a better solution. I've posted my eventual solution below, but I'd be thrilled (and maybe just a little mortified) to discover there is some mind-blowingly simple solution that has escaped me this whole time. Or any other solution that meets my criteria:
it must be able to sort by MostRecentComment fields at the Model::find level (ie. not just a massage of the results);
it shouldn't require additional fields in the comments or blog_entries tables;
it should respect the 'spirit' of the CakePHP ORM.
(I'm also not sure the title of this question is as concise/informative as it could be.)
