Merge pull request #775 from pozorvlak/speed_up_homepage

Speed up homepage by calculating "interesting" things more efficiently

app/models/crop.rb

@@ -29,6 +29,12 @@ class Crop < ActiveRecord::Base
   scope :pending_approval, -> { where(:approval_status => "pending") }
   scope :approved, -> { where(:approval_status => "approved") }
   scope :rejected, -> { where(:approval_status => "rejected") }
+  # Crops with enough plantings and photos
+  # ActiveRecord wizardry copied from
+  # http://stackoverflow.com/questions/13226913/how-do-i-select-all-records-with-more-than-n-child-records
+  scope :has_plantings, ->(min_plantings) { select("crops.*").joins(:plantings).group("crops.id").having("count(crops.id) >= ?", min_plantings) }
+  scope :has_photos, ->(min_photos) { select("crops.*").joins(:photos).group("crops.id").having("count(crops.id) >= ?", min_photos) }
+  scope :interesting, -> { has_plantings(3).has_photos(3).randomized.limit(12) }
 
   ## Wikipedia urls are only necessary when approving a crop
   validates :en_wikipedia_url,
@@ -174,14 +180,6 @@ class Crop < ActiveRecord::Base
     return popular_plant_parts
   end
 
-  def interesting?
-    min_plantings = 3 # needs this many plantings to be interesting
-    min_photos    = 3 # needs this many photos to be interesting
-    return false unless photos.size >= min_photos
-    return false unless plantings_count >= min_plantings
-    return true
-  end
-
   def pending?
     approval_status == "pending"
   end
@@ -202,19 +200,6 @@ class Crop < ActiveRecord::Base
     [ "already in database", "not edible", "not enough information", "other" ]
   end
 
-  # Crop.interesting
-  # returns a list of interesting crops, for use on the homepage etc
-  def Crop.interesting
-  howmany = 12 # max number to find
-  interesting_crops = Array.new
-    Crop.randomized.each do |c|
-      break if interesting_crops.size == howmany
-      next unless c.interesting?
-      interesting_crops.push(c)
-    end
-    return interesting_crops
-  end
-
 # Crop.create_from_csv(row)
 # used by db/seeds.rb and rake growstuff:import_crops
 # CSV fields:

app/models/planting.rb

@@ -90,10 +90,6 @@ class Planting < ActiveRecord::Base
     return photos.first
   end
 
-  def interesting?
-    return photos.present?
-  end
-
   def calculate_days_before_maturity(planting, crop)
     p_crop = Planting.where(:crop_id => crop).where.not(:id => planting)
     differences = p_crop.collect do |p|
@@ -113,19 +109,15 @@ class Planting < ActiveRecord::Base
   # we can't do this via a scope (as far as we know) so sadly we have to
   # do it this way.
   def Planting.interesting(howmany=12, require_photo=true)
-    interesting_plantings = Array.new
-    seen_owners = Hash.new(false) # keep track of which owners we've seen already
-
-    Planting.all.each do |p|
-      break if interesting_plantings.size == howmany # got enough yet?
-      if require_photo
-        next unless p.photos.present? # skip those without photos, if required
-      end
-      next if seen_owners[p.owner]  # skip if we already have one from this owner
-      seen_owners[p.owner] = true   # we've seen this owner
-      interesting_plantings.push(p)
+    if require_photo then
+      candidates = Planting.joins(:photos).uniq
+    else
+      candidates = Planting
     end
-
-    return interesting_plantings
+    # Find the most recent acceptable planting for each member
+    most_recent_ids = candidates.select("max(plantings.id)")
+                                .unscope(:order)
+                                .group("plantings.owner_id")
+    return candidates.where(id: most_recent_ids).limit(howmany)
   end
 end