Validating longitude / latitude with geocoder gem - ruby-on-rails

Question

I followed this Geocoder Railscast & I'm playing around with it to see if I can add validation to the longitude & latitude coordinates returned by the Geocoder Gem incase the user inputs a faulty address that does not return any longitude & latitude coordinates.
I was able to get this working to a point with the code below but when I enter a correct address it gives the user a validation error the first time they submit the form, even though longitude & latitude coordinates where returned. The second time the user submits the form it works.
I suspect this is happening as when the user submits the form there are no longitude & latitude coordinates but there are the second time round as the geocoder gem returned the coordinates.
Is there something wrong with my code or should I be approaching this differently?
Model
class Location < ActiveRecord::Base
attr_accessible :address1,
:country,
:latitude,
:longitude,
:name
validates :latitude, :presence => {message: "Not a valid location on Google Maps, please check name address & country fields" }
geocoded_by :address
after_validation :geocode, :if => :address_changed?
def address
[name, address1, country].compact.join(' ')
end
def address_changed?
attrs = %w(name address1 country)
attrs.any?{|a| send "#{a}_changed?"}
end
end
Terminal OutPut
=> Booting WEBrick
=> Rails 3.2.12 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
[2013-04-02 02:03:41] INFO WEBrick 1.3.1
[2013-04-02 02:03:41] INFO ruby 1.9.3 (2013-02-22) [x86_64-linux]
[2013-04-02 02:03:41] INFO WEBrick::HTTPServer#start: pid=4316 port=3000
Started POST "/locations" for 127.0.0.1 at 2013-04-02 02:04:04 +0100
Processing by LocationsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"4HUay+IOgA7JnCSg8ZZ0zVMcHpj7djUPlfqe1emTMSY=", "location"=>{"name"=>"Louch Dan", "address1"=>"Roundwood", "town"=>"", "county"=>"", "state"=>"", "country"=>"Ireland", "latitude"=>"", "longitude"=>""}, "commit"=>"Create Location"}
(0.1ms) begin transaction
(0.1ms) rollback transaction
Rendered locations/_form.html.erb (8.9ms)
Rendered locations/new.html.erb within layouts/application (63.4ms)
Completed 200 OK in 410ms (Views: 156.1ms | ActiveRecord: 6.0ms)
Started GET "/assets/application.css?body=1" for 127.0.0.1 at 2013-04-02 02:04:06 +0100
Served asset /application.css - 304 Not Modified (11ms)
[2013-04-02 02:04:06] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
Started GET "/assets/jquery_ujs.js?body=1" for 127.0.0.1 at 2013-04-02 02:04:06 +0100
Served asset /jquery_ujs.js - 304 Not Modified (1ms)
[2013-04-02 02:04:06] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
Started GET "/assets/jquery.js?body=1" for 127.0.0.1 at 2013-04-02 02:04:06 +0100
Served asset /jquery.js - 304 Not Modified (7ms)
Started GET "/assets/scaffolds.css?body=1" for 127.0.0.1 at 2013-04-02 02:04:06 +0100
Served asset /scaffolds.css - 304 Not Modified (1ms)
Started GET "/assets/locations.css?body=1" for 127.0.0.1 at 2013-04-02 02:04:06 +0100
Served asset /locations.css - 304 Not Modified (1ms)
[2013-04-02 02:04:06] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
[2013-04-02 02:04:06] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
Started GET "/assets/locations.js?body=1" for 127.0.0.1 at 2013-04-02 02:04:06 +0100
Served asset /locations.js - 304 Not Modified (4ms)
[2013-04-02 02:04:06] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
[2013-04-02 02:04:06] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
Started GET "/assets/application.js?body=1" for 127.0.0.1 at 2013-04-02 02:04:06 +0100
Served asset /application.js - 304 Not Modified (7ms)
[2013-04-02 02:04:06] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
Started POST "/locations" for 127.0.0.1 at 2013-04-02 02:04:22 +0100
Processing by LocationsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"4HUay+IOgA7JnCSg8ZZ0zVMcHpj7djUPlfqe1emTMSY=", "location"=>{"name"=>"Louch Dan", "address1"=>"Roundwood", "town"=>"", "county"=>"", "state"=>"", "country"=>"Ireland", "latitude"=>"53.07004130000001", "longitude"=>"-6.2804327"}, "commit"=>"Create Location"}
(0.1ms) begin transaction
SQL (15.3ms) INSERT INTO "locations" ("address1", "country", "county", "created_at", "latitude", "longitude", "name", "state", "town", "updated_at") VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?) [["address1", "Roundwood"], ["country", "Ireland"], ["county", ""], ["created_at", Tue, 02 Apr 2013 01:04:22 UTC +00:00], ["latitude", 53.07004130000001], ["longitude", -6.2804327], ["name", "Louch Dan"], ["state", ""], ["town", ""], ["updated_at", Tue, 02 Apr 2013 01:04:22 UTC +00:00]]
(71.9ms) commit transaction
Redirected to http://0.0.0.0:3000/locations/10
Completed 302 Found in 236ms (ActiveRecord: 87.3ms)
Started GET "/locations/10" for 127.0.0.1 at 2013-04-02 02:04:22 +0100
Processing by LocationsController#show as HTML
Parameters: {"id"=>"10"}
Location Load (3.8ms) SELECT "locations".* FROM "locations" WHERE "locations"."id" = ? LIMIT 1 [["id", "10"]]
Rendered locations/show.html.erb within layouts/application (9.8ms)
Completed 200 OK in 25ms (Views: 15.5ms | ActiveRecord: 3.8ms)
Started GET "/assets/application.css?body=1" for 127.0.0.1 at 2013-04-02 02:04:22 +0100
Served asset /application.css - 304 Not Modified (0ms)
[2013-04-02 02:04:22] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
Started GET "/assets/locations.css?body=1" for 127.0.0.1 at 2013-04-02 02:04:22 +0100
Served asset /locations.css - 304 Not Modified (0ms)
[2013-04-02 02:04:22] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
Started GET "/assets/jquery_ujs.js?body=1" for 127.0.0.1 at 2013-04-02 02:04:22 +0100
Served asset /jquery_ujs.js - 304 Not Modified (0ms)
Started GET "/assets/jquery.js?body=1" for 127.0.0.1 at 2013-04-02 02:04:22 +0100
Served asset /jquery.js - 304 Not Modified (6ms)
[2013-04-02 02:04:22] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
[2013-04-02 02:04:22] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
Started GET "/assets/scaffolds.css?body=1" for 127.0.0.1 at 2013-04-02 02:04:22 +0100
Served asset /scaffolds.css - 304 Not Modified (0ms)
[2013-04-02 02:04:22] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
Started GET "/assets/application.js?body=1" for 127.0.0.1 at 2013-04-02 02:04:22 +0100
Served asset /application.js - 304 Not Modified (43ms)
Started GET "/assets/locations.js?body=1" for 127.0.0.1 at 2013-04-02 02:04:22 +0100
Served asset /locations.js - 304 Not Modified (0ms)
[2013-04-02 02:04:22] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true
[2013-04-02 02:04:22] WARN Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true

Answer 1

Why can't you :geocode the Location before validation? :address_changed? will return true even for new records if any of those fields have changed. Validate it and if it returns invalid lat/lng values then your :latitude presence validation will fail.
Just change that after_validation to before_validation.