On Aug 31, 12:39 am, Colin Law <clan...@googlemail.com> wrote: > 2009/8/31 Tony <tony.cassan...@gmail.com>: > > > > > Maybe I'm missing something but I don't see any way to get eager > > loading with the named scopes. I have many Event models each with > > many Stat models. If I have to query each event to get the summary, I > > still have the n+1 query problem. > > Don't follow you here, it should be just one query for each event to > get the stat summary for that event. > > Colin > > > Maybe the best solution is to > > define a second model referencing the same table but with a different > > default scope? That doesn't seem like it is the most concise solution > > but it may be the cleanest and easiest to read. > > > I think the ideal solution would be the ability to reference a named > > scope of a joined model. E.g: > > > Event: > > has_one :summary, :class_name => 'Stat', :scope => :summary > > > Does that make sense? Is there some other way that I'm overlooking? > > Thanks again! > > > tony > > > On Aug 30, 2:36 pm, Tony <tony.cassan...@gmail.com> wrote: > >> Thanks for the quick response! I'm not familiar with the named > >> scopes. Will these work with preloading the records (I assume by > >> using (:include => [:stats])? I could end up with a ton of Events on > >> one page and I'd prefer not to have to fetch the summary for every > >> one. I also assume I'd reference it by doing event.stats.summary? > >> That seems a lot cleaner. I'll go dig into this a bit. Thanks! > > >> tony > > >> On Aug 30, 2:24 pm, Colin Law <clan...@googlemail.com> wrote: > > >> > 2009/8/30 Tony <tony.cassan...@gmail.com>: > > >> > > So I'd like to set up the below associations. An Event is a normal AR > >> > > model. Stat is a normal AR model. I want a special stat on Event > >> > > that is a DB computation (mostly just sums of each column) and a > >> > > summary of all the Stats for that Event. The Summary isn't persisted > >> > > and is marked as readonly. Unfortunately, preloading is important in > >> > > this case (and thus why I went off on the group_by tangent, sorry if > >> > > that wasn't clear). > > >> > > I guess I could make a new model for Summary referencing the stats > >> > > table which uses a special select and always adds the group by clause, > >> > > however, that seemed like overkill. I really didn't want to run a > >> > > loop over the returned stats since the DB can give me exactly what I'm > >> > > looking for on the initial query. > > >> > > Ok, here's a slightly abridged version of what I thought might work: > > >> > > Event: > >> > > has_many :stats > >> > > has_one :summary_stat, :select => "sum(people) as > >> > > people, ...", :class_name => 'Stat', :foreign_key => > >> > > 'event_id', :readonly => true > > >> > > Stat: > >> > > belongs_to :event > > >> > > Adding "group" to the has_one solves the issue, but am I going about > >> > > this in the "right" way? Thanks for the input! > > >> > > tony > > >> > I don't think I would go about it this way. Using Event has_one > >> > summary_stat suggests that somewhere there is a model SummaryStat that > >> > belongs_to event. > >> > An alternative would be to define an appropriate named scope in Stat > >> > that provides the summed stats using the single query and provide a > >> > read only attribute of Event that calls it and provides the answer. > > >> > Colin
Ooops, sorry about that. So it is indeed one query per event, however, I need a list of N events all at the same time. I didn't mean to imply that it is N queries per event, rather that it is N queries per page load. The page is loading N events and their summaries (kinda like a dashboard...). This means that I'd need a query for every Event to fetch the summary, thus the N queries, + 1 for the initial fetching of the events. If I were to stuff this in an association I'd have 2 queries only (one for the events and one for all of the summaries). If I were only displaying a few Events per page I wouldn't be concerned, however, 10, 20, 30+ queries for a single page would begin to impact performance, I imagine. I'd really like to replicate the performance of a find using :include. If the only way to get that performance is to use a separate model (SummaryStat) and mark it as readonly, I'm happy to do it. I was simply hoping for a more concise and readable way of doing this. I got very close to being able to do it in a concise way using the normal has_* relationships, however, has_one doesn't support grouping which I needed for this particular query. Thanks again for bearing with me on this. I appreciate all your help. tony --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk@googlegroups.com To unsubscribe from this group, send email to rubyonrails-talk+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
