Undefined method for array csv export - ruby-on-rails

Question

I'm getting the following error when trying to export to a csv:
undefined method `dd_export' for #<Array:0x00007fc4836f1798>
I think it's the relationship between the model and controller, but can't work out why this is. I'm using a custom dd_export convention as more csv download may be added, and also using to_csv doesn't seem to export what's required in my model.
day_degree_export.rb
class DayDegreeExport < ApplicationRecord
def self.dd_export
attributes = %w{Date Min_Temp Max_Temp}
CSV.generate(headers: true) do |csv|
csv << attributes
all.each do |dd|
csv << [
dd['date'],
dd['variables'][1]['value']
dd['variables'][0]['value']
]
end
end
end
end
end
day_degree_export_controller.rb
class DayDegreeExportController < ApplicationController
dd_results
data = HTTParty.get("url_link")
#ddexport = JSON.parse(data.body)
respond_to do |format|
format.html
format.csv { send_data #ddexport['data'].dd_export, filename: "ddexport.csv" }
end
end
end
I have required csv in my application.rb.

Answer 1

If you want to call #ddexport['data'].dd_export, you'd have to patch the Array class for dd_export, but a better way to implement it is to save your array as DayDegreeExport records.
class DayDegreeExportController < ApplicationController
def dd_results
data = HTTParty.get("url_link")
#ddexport = JSON.parse(data.body)
DayDegreeExport.create(#ddexport) # you can do this if your #ddexport is array of hashes with matching keys
respond_to do |format|
format.html
format.csv { send_data DayDegreeExport.dd_export, filename: "ddexport.csv" }
end
end
end

Answer 2

Since you are not intending to store #ddexport['data'], then there is no need for DayDegreeExport to inherit from ApplicationRecord. Instead, I would suggest you do something like:
# app/services/day_degree_export_service.rb
class DayDegreeExportService
CSV_ATTRIBUTES = %w(
Date
Min_Temp
Max_Temp
).freeze
attr_accessor *%w(
args
).freeze
class << self
def call(args={})
new(args).call
end
end
def initialize(args)
#args = args
end
def call
CSV.generate(headers: true) do |csv|
csv << CSV_ATTRIBUTES
dd_export_data.each do |dd|
csv << [
dd['date'],
dd['variables'][1]['value']
dd['variables'][0]['value']
]
end
end
end
private
def dd_export_data
#dd_export_data ||= JSON.parse(HTTParty.get("url_link"))['data']
end
end
Which you would use something like:
class DayDegreeExportController < ApplicationController
def dd_results
respond_to do |format|
format.html
format.csv { send_data DayDegreeExportService.call, filename: "ddexport.csv" }
end
end
end
Now, a few comments:
1) I never use CSV so I have no idea whether the code is going to work. I took a look at the docs and I think this may be close, but you may have to fiddle with it.
2) A PORO (plain old ruby object) gets the job done here. You can see I suggest you place it in a services directory and rails will pick it up automatically.
3) In the class-level call method, I include optional args. That's just for example purposes. Some other time you might want to pass in arguments.
4) For services, I like to use the call method instead of service-specific methods like dd_results. It's just a me thing. But, then, you don't have to think about what to call your methods in your service. As long as your services and their purpose have a 1:1 relationship, then the class name describes what the service does instead of the method name.
5) Using class << self creates class methods. It's basically the same as doing def self.call.
6) This all assumes, I supposed, that JSON.parse(HTTParty.get("url_link"))['data'] returns an array of data and that each datum has the keys that you indicate.