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More work on optimisation the location of nearby users - it turns out

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that getting the database to do the filtering is much better as it
avoids us constructing thousands of user objects only to then throw
most of them away again.
This commit is contained in:
Tom Hughes 2009-06-05 09:30:31 +00:00
parent 857eeae8b2
commit 5de81dc4b0
2 changed files with 8 additions and 3 deletions
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6
app/models/user.rb
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@ -98,9 +98,9 @@ class User < ActiveRecord::Base
if self.home_lon and self.home_lat
gc = OSM::GreatCircle.new(self.home_lat, self.home_lon)
bounds = gc.bounds(radius)
nearby = User.find(:all, :conditions => ["visible = ? and home_lat between #{bounds[:minlat]} and #{bounds[:maxlat]} and home_lon between #{bounds[:minlon]} and #{bounds[:maxlon]} and data_public = ? and id != #{self.id}", true, true])
nearby = nearby.sort_by { |u| gc.distance(u.home_lat, u.home_lon) }.first(num)
nearby.delete_if { |u| gc.distance(u.home_lat, u.home_lon) > radius }
sql_for_distance = gc.sql_for_distance("home_lat", "home_lon")
nearby = User.find(:all,
:conditions => ["id != ? AND visible = ? AND data_public = ? AND #{sql_for_distance} <= ?", id, true, true, radius], :order => sql_for_distance, :limit => num)
else
nearby = []
end

5
lib/osm.rb
View file

@ -334,6 +334,11 @@ module OSM
maxlon = (@lon + lonradius) * 180 / PI
return { :minlat => minlat, :maxlat => maxlat, :minlon => minlon, :maxlon => maxlon }
end
# get the SQL to use to calculate distance
def sql_for_distance(lat_field, lon_field)
"6372.795 * 2 * asin(sqrt(power(sin((radians(#{lat_field}) - #{@lat}) / 2), 2) + cos(#{@lat}) * cos(radians(#{lat_field})) * power(sin((radians(#{lon_field}) - #{@lon})/2), 2)))"
end
end
class GeoRSS