Ruby on Rails optimalization of some code - mysql

Question

I have some simple code that uses the minmax algoritm to locate birds. Everything works but I find my programming not good and I believe there is a better solution. I'm not that experienced in RoR but if somebody knows a better way to achieve the same solution then I'm greatful ;).
There are two parts I hate, the 4 lists I had to create to determine the max or min value for the different combinations (the core of the min-max algorithm) and the very ugly SQL hack.
Thanks!
def index
# fetch all our birds
#birds = Bird.all
# Loop over the birds
#birds.each do |bird|
#fixed = Node.where("d7type = 'f'")
xminmax = []
xmaxmin = []
yminmax = []
ymaxmin = []
#fixed.each do |fixed|
rss = Log.find_by_sql("SELECT logs.fixed_mac, AVG(logs.blinker_rss) AS avg_rss FROM logs
WHERE logs.blinker_mac = '#{bird.d7_mac}' AND logs.fixed_mac = '#{fixed.d7_mac}' ORDER BY logs.id DESC LIMIT 30")
converted_rss = calculate_distance_rss(rss[0].attributes["avg_rss"])
xminmax.push(fixed.xpos + converted_rss)
xmaxmin.push(fixed.xpos - converted_rss)
yminmax.push(fixed.ypos + converted_rss)
ymaxmin.push(fixed.ypos - converted_rss)
end
pos = {x: (xminmax.min + xmaxmin.max) / 2, y: (yminmax.min + ymaxmin.max) / 2}
puts pos
end
end

Answer 1

2 things you could do to start with is (assuming Birds could be a large table) Change Bird.all to
Bird.find_each do |bird|
... code ...
end
It's a more efficient way to loop over many table records.
2nd: take #fixed = Node.where("d7type = 'f'") out of the each loop since it doesn't need any variables for its query. Put it above the loop so it doesn't execute each time.
3rd (Not so much of an optimization but just safer code): Your Log.find_by_sql looks simple enough to use active_record, you can change it to:
Log.select('fixed_mac, AVG(logs.blinker_rss) AS avg_rss, blinker_mac').
where(blinker_mac: bird.d7_mac, fixed_mac: fixed.d7_mac).
order('id DESC').limit(30)
converted_rss = calculate_distance_rss(rss.first.avg_rss)
Everything else looks fine.