Question

I have an application that allows users to save events. I would like to be able to see which events are being saved the most over the past week. To do this, I created a ‘trending’ function in my Event model and then tried accessing that in my view. That returns an error.

_trending.html.erb:

missing attribute: is_public
Extracted source (around line #3):

1: 
2: <% 
3:   events = Event.trending( :timespan => 1.week, :limit => 25 )
4: %>

This is the trending function in my event model. I decided to code it in raw SQL (postgres db) so there would be no confusion about how ActiveRecord is building my query.

event.rb:

def self.trending(options={})
  limit = options[:limit]
  span = options[:timespan]

  earliest_save = (Time.now - span)
  event_sql = %( SELECT events.title, saved_events.event_id, COUNT(user_id) as save_count, MAX(saved_events.created_at) as created 
                 FROM saved_events, events
                 WHERE events.id = saved_events.event_id AND saved_events.is_public = TRUE AND saved_events.created_at >= '#{earliest_save}'
                 GROUP BY saved_events.event_id, events.title
                 ORDER BY save_count DESC, created DESC
                 LIMIT #{limit} )

  find_by_sql( "#{event_sql}" )
end

So the rows that should be returned by this function should only include the fields title, event_id, and save_count. Why is it looking for is_public? I get the impression that it somehow expects an actual instance of an Event object. If that is the case, how do I rewrite this?

Update in response to questions about is_public:
is_public is definitely a column in saved_events. I did run the migration. To isolate this further, I removed the ‘AND saved_events.is_public = TRUE’ from the SQL and still got the same error. The SQL is valid, and I checked that it works in pgAdmin.

Answer 1

I think the issue stems from the way find_by_sql works, as documented in the API.

If you call a complicated SQL query which spans multiple tables the columns specified by the SELECT will be attributes of the model, whether or not they are columns of the corresponding table.
http://apidock.com/rails/ActiveRecord/Base/find_by_sql/class

I rewrote the query the Rails-way™ and was able to get rid of the SELECT statement. This code worked perfectly.

time_range = (Time.now - span)..Time.now
joins(:saved_events).where( :saved_events => { :created_at => time_range, :is_public => true } )
                    .group( "saved_events.event_id, events.id" )
                    .order( "COUNT(saved_events.user_id) DESC, MAX(saved_events.created_at) DESC" )
                    .limit( limit )