Sum of values in loop and keeping highest value - ruby-on-rails

Question

I am trying to calculate the shipping dimensions of multiple products. I want to return the largest value of #tempLength and #tempWidth and sum up all #tempHeights in my loop:
#tempLength = 0
#tempWidth = 0
#tempHeight = 0
params[:rate][:items].each do |item|
item = item[:product_id]
puts "Item details"
puts item
#productDimensions = Product.where(:product_id => item).first
#tempLength = #productDimensions.length
#tempWidth = #productDimensions.width
#tempHeight = #productDimensions.height
# tempLength = maximum length value
# tempWidth = maximum width value
# tempHeight = sum of all heights
end
I know I have to use sum(&:symbol), but I'm stuck. What's the best approach?

Answer 1

here probably can help
#tempLength = 0
#tempWidth = 0
#tempHeight = 0
params[:rate][:items].each do |item|
item = item[:product_id]
puts "Item details"
puts item
#productDimensions = Product.where(:product_id => item).first
#tempLength = #tempLength + #productDimensions.length
#tempWidth = #tempWidth + #productDimensions.width
if #productDimensions.height > #tempHeight
#tempHeight = #productDimensions.height
end
end
# #tempLength = total of all tempLength values
# #tempWidth = total of all tempHeight values
# #tempHeight = keep highest value

Answer 2

Maybe another suggestion that may result in better performance:
#tempLength = 0
#tempWidth = 0
#tempHeight = 0
product_ids = []
params[:rate][:items].each do |item|
product_ids << item[:product_id]
end
# Filter products according to collected product_ids
#products = Product.where(:product_id => product_ids)
# Let ActiveRecord do the work
#tempLength = #products.sum('length')
#tempWidth = #products.sum('width')
#tempHeight = #products.maximum('height')
# #tempLength = total of all tempLength values
# #tempWidth = total of all tempHeight values
# #tempHeight = keep highest value