How find the distance between two objects? - ruby-on-rails

Question

Im using geocode. The idea is our partners can post products with an address. When they do so it fetches the latitude and longitude. Now when our customers go to buy that product they have to enter in a delivery address to tell us where to deliver the product. However if they delivery address is not within 20 miles of the product they are not allowed to get the product delivered.
Im getting an error message saying this "undefined method `latitude' for nil:NilClass"
Like I said the product.longitude, product.latitude is already set when the users are trying to order.
Not sure if it's because the order.delivery_address(lat, long) is not submitted into the database yet and its trying to check the distance. Here my code below
So My question is how can is how can i find the distance between the product address and order address and I want to show a alert message to the user if the distance between the two is over 20 miles.
def create
product = Product.find(params[:product_id])
if current_user == product.user
flash[:alert] = "You cannot purchase your own property"
elsif current_user.stripe_id.blank? || current_user.phone_number.blank?
flash[:alert] = " Please update your payment method and verify phone number please"
return redirect_to payment_method_path
elsif Geocoder::Calculations.distance_between([product.latitude, product.longitude], [#order.latitude, #order.longitude]) < 20
flash[:alert] = "The delivery address you provided is outside the delivery zone. Please choose a different product."
else
quantity = order_params[:quantity].to_i
#order = current_user.orders.build(order_params)
#order.product = product
#order.price = product.price
#order.total = product.price * quantity + product.delivery_price
# #order.save
if #order.Waiting!
if product.Request?
flash[:notice] = "Request sent successfully... Sit back and relax while our licensed dispensary fulfil your order :)"
else
#order.Approved!
flash[:notice] = "Your order is being filled and it will delivered shortly:)"
end
else
flash[:alert] = "Our licensed dispensary cannot fulfil your order at this time :( "
end
end
redirect_to product
end

Answer 1

You set #order in the following line:
#order = current_user.orders.build(order_params)
But you try to call its longitude and latitude methods above this, before you even set #order variable. To simply fix this problem, you can move this line up, it can even be located at the beginning of create method, since it doesn't depend on product or anything like that:
def create
#order = current_user.orders.build(order_params)
# ...
end
Although, there are number of problems in your code, like method names starting with capital letters (you can do it, but you shouldn't, it's against the convention) or overall complexity of the method.

Answer 2

You should move the business logic to the model where it belongs.
So lets start by creating a validation for the product distance:
class Order < ApplicationRecord
validates :product_is_within_range,
if: -> { product.present? } # prevents nil errors
# our custom validation method
def product_is_within_range
errors.add(:base, "The delivery address you provided is outside the delivery zone. Please choose a different product.") if product_distance < 20
end
def product_distance
Geocoder::Calculations.distance_between(product.coordinates, self.coordinates)
end
end
Then move the calculation of the total into the model:
class Order < ApplicationRecord
before_validation :calculate_total!, if: ->{ product && total.nil? }
def calculate_total!
self.total = product.price * self.quantity + product.delivery_price
end
end
But then you still have to deal with the fact that the controller is very broken. For example:
if current_user == product.user
flash[:alert] = "You cannot purchase your own property"
Should cause the method to bail. You´re not actually saving the record either. I would start over. Write failing tests for the different possible conditions (invalid parameters, valid parameters, user is owner etc) then write your controller code. Make sure you test each and every code branch.