I have a Team class that contains a find_team class method. The method returns a Team object if one is found, or nil if no object is found:
class Team
##all_teams = []
def self.find_team(name)
index = ##all_teams.find_index { |t| t.name == name }
if index.nil?
nil
else
##all_teams[index]
end
end
end
In implementing the class, I need to assign a variable to the correct Team object if it exists or create a new Team object if it doesn't. I'm struggling with finding the clearest, quickest, ruby-ist way to do it. Some options I've considered:
t1 = Team.find_team("Some Team") ? Team.find_team("Some Team") : Team.new("Some Team")
t2 = Team.find_team("Some Other Team")
t2 ||= Team.new("Some Other Team")
t3 = if Team.find_team("Another Team")
Team.find_team("Another Team")
else
Team.new("Another Team")
I favor the second example, as it's less verbose and repetitive, but I'm wondering if there's some Ruby trick I'm missing in this scenario.
t1 = Team.find_team("Some Team") || Team.new("Some Team")
is probably the most Ruby-ish version. You can also consider to enhance your custom method.
As a side note, you can refactor your find_team method to use Enumerable#find
class Team
##all_teams = []
def self.find_team(name)
##all_teams.find { |t| t.name == name }
end
end
And you can also add a new method that returns the instance if none
class Team
##all_teams = []
def self.find_team(name)
##all_teams.find { |t| t.name == name }
end
def self.find_or_build_team(name)
find_team(name) || Team.new(name)
end
end
so that you will just call
Team.find_or_build("Some Team")
How about:
t1 = Team.find_team('Some Team') || Team.new('Some Team')
This assigns a new Team instance into t1 only if find_team method returns nil.
Related
Background
The Entity class is a base class that gets inherited by several subclasses that holds entities received over a REST API. The entity classes are immutable and should return a new instance of themselves whenever a change is attempted.
The Entity class has an .update() method that takes a hash of values to update, if the changes aren't really changes it returns itself and if there are real changes it returns a new instance of itself with the changes effected before instantiation.
To be user friendly Entity also allows for direct assignment to properties (so that if a subclass of Entity has a name attribute you can do instance.name = 'New Name') that also returns a new instance of the class. This is implemented in terms of update using dynamic methods that are created when the class is instantiated.
And they are the problem.
Problem
The code in the Entity class looks, in part, like this (for a complete code listing and tests check out the Github repo: https://github.com/my-codeworks/fortnox-api.git):
require "virtus"
require "ice_nine"
class Entity
extend Forwardable
include Virtus.model
def initialize( hash = {} )
super
create_attribute_setter_methods
IceNine.deep_freeze( self )
end
def update( hash )
attributes = self.to_hash.merge( hash )
return self if attributes == self.to_hash
self.class.new( attributes )
end
private
def create_attribute_setter_methods
attribute_set.each do |attribute|
name = attribute.options[ :name ]
create_attribute_setter_method( name )
end
end
def create_attribute_setter_method( name )
self.define_singleton_method "#{name}=" do | value |
self.update( name => value )
end
end
end
Doing this:
instance.update( name: 'New Name' )
and this:
instance.name = 'New Name'
Should be the same, literally since one is implemented in terms of the other.
While .update() works perfectly the .attr=() methods return the value you assign.
So in the above example .update() returns a new instance of the Entity subclass but .attr=() returns 'New Name' ...
I have tries capturing the output inside the .attr=() method and log it before returning so that I have this:
self.define_singleton_method "#{name}=" do | value |
p "Called as :#{name}=, redirecting to update( #{name}: #{value} )"
r = self.update( name => value )
p "Got #{r} back from update"
return r
end
And the log lines say:
"Called as :name=, redirecting to update( name: 'New Name' )"
"Got #<TestEntity:0x007ffedbd0ad18> back from update"
But all I get is the string 'New Name'...
My forehead is bloody and no posts I find show anything close to this. I bet I'm doing something wrong but I can't find it.
Getting dirty
The Github repo has tests in rspec that you can run, the failing ones are focused right now and some extra logging is in the Entity class to capture the different internal steps.
Comments, links and/or pull requests are welcome.
Turns out that the = methods always return the value being assigned.
o = Struct.new(:key).new(1)
o.define_singleton_method("something") { #something }
o.define_singleton_method("something=") do |v|
#something = v
return 6
end
As you can see, I've 'fixed' the return value to 6 each time something= is called. Let's see if it works:
o.something = 1 #=> outputs 1, not 6
o.something #=> outputs 1, so the method did indeed run
Conclusion? My guess is that an = method will return the value that you are assigning through it. And IMO it's better this way; one reason would be to ensure proper functioning of assignment chains:
new_val = o.something = some_val
Here's an extract of the code that I am using:
def retrieve(user_token, quote_id, check="quotes")
end_time = Time.now + 15
match = false
until Time.now > end_time || match
#response = http_request.get(quote_get_url(quote_id, user_token))
eval("match = !JSON.parse(#response.body)#{field(check)}.nil?")
end
match.eql?(false) ? nil : #response
end
private
def field (check)
hash = {"quotes" => '["quotes"][0]',
"transaction-items" => '["quotes"][0]["links"]["transactionItems"]'
}
hash[check]
end
I was informed that using eval in this manner is not good practice. Could anyone suggest a better way of dynamically checking the existence of a JSON node (field?). I want this to do:
psudo: match = !JSON.parse(#response.body) + dynamic-path + .nil?
Store paths as arrays of path elements (['quotes', 0]). With a little helper function you'll be able to avoid eval. It is, indeed, completely inappropriate here.
Something along these lines:
class Hash
def deep_get(path)
path.reduce(self) do |memo, path_element|
return unless memo
memo[path_element]
end
end
end
path = ['quotes', 0]
hash = JSON.parse(response.body)
match = !hash.deep_get(path).nil?
Forgive me if my question isn't completely clear. I have been awake for way too long and I'm feeling a little brain dead.
I'm doing a Ruby exercise and I can't figure out why my rspec test isn't passing for something I thought would work.
require 'date'
class Product
attr_accessor :photo_src, :promotion, :initial_date
attr_reader :default_photo, :default_price, :current_price
def initialize(name, photo, price)
#name = name
#default_photo = photo
#photo_src = photo
#default_price = price
#current_price = price
#initial_date = Date.today.yday
#promotion = false
end
def price_change(sale_price)
calculator = RedPencilCalculator.new(self)
if promotion
if sale_price > #current_price
calculator.end_promotion!
elsif sale_price < (#default_price - (#default_price * 0.3))
calculator.end_promotion!
end
else
calculator.start_promotion!
end
#current_price = sale_price
end
end
class RedPencilCalculator
attr_accessor :promotion_start, :product
def initialize(product)
#product = product
end
def start_promotion!
if start_promotion?
product.promotion = true
product.photo_src = "redX.png"
#promotion_start = Date.today.yday
end
end
#would need to run daily
def end_promotion?
promotion_duration
if #duration == 30 || #duration == 335
end_promotion!
end
end
def end_promotion!
product.promotion = false
product.photo_src = product.default_photo
product.initial_date = Date.today.yday
end
private
def calculate_range
#min_discount = product.default_price - (product.default_price * 0.05)
#max_discount = product.default_price - (product.default_price * 0.3)
end
def start_promotion?
calculate_range
#max_discount <= product.current_price && product.current_price <= #min_discount && Date.today.yday - product.initial_date >= 30
end
def promotion_duration
current_date = Date.today.yday
#duration = current_date - #promotion_start
end
end
Rspec
This doesn't work:
describe Product do
let(:shoes) { Product.new("shoes", "item.png", 100) }
it 'should change the photo_src and promotion attribute if applicable' do
allow(shoes).to receive(:initial_date) { 100 }
shoes.price_change(75)
expect(shoes.promotion).to eq(true)
expect(shoes.photo_src).to eq("redX.png")
end
end
This does:
describe Product do
let(:shoes) { Product.new("shoes", "item.png", 100) }
let(:calculator) { RedPencilCalculator.new(shoes) }
it 'should change the photo_src and promotion attribute if applicable' do
allow(shoes).to receive(:initial_date) { 100 }
shoes.price_change(75)
calculator.start_promotion!
expect(shoes.promotion).to eq(true)
expect(shoes.photo_src).to eq("redX.png")
end
end
So it seems to me that the start_promotion! method call in the price_change method just isn't working.
I don't have a specific answer to your bug but some suggestions on how to pinpoint the problem.
You're testing too much in one unit test. There's so much that can go wrong it's hard (as you've found) to track down where the bug lies. Even if you work it out now, when something changes down the track (as it inevitably will) it will be at least as difficult as it is now to debug.
Simplify the initializer. It should only set #name, #photo, #price. The other instance variables should be methods (write tests unless they're private).
You suspect RedPencilCalculator#start_promotion! has a bug. Write a test to eliminate that possibility.
With more tests in place, the bug will eventually be cornered and crushed!
Lastly - this is easier said than done - but try writing tests first. It is hard but gets easier and even enjoyable!
ok, I put a puts inside of start_promotion? like this:
p "got past calc range: #{#max_discount.inspect} and #{#min_discount.inspect} and #{product.current_price}"
and got:
"got past calc range: 70.0 and 95.0 and 100"
given that the following line checks that current-price is less than the min-discount...
that's the line you've gotta check/fix to make things work
I have this code that tries to return a value from a method:
temp = "123"
return temp
and I have this line that calls the method and assigns the return value:
person_connections = #client.get_person_connections(:id => current_user_id )
but when I try to inspect person_connections, it shows some different object string. Any idea how to return the actual value of the temp variable?
def get_person_connections(options = {})
person_id = options[:id]
path = "/people/id=" + person_id + ":(num-connections)"
query_connections(path, options)
self
end
and
private
def query_connections(path, options={})
fields = options.delete(:fields) || LinkedIn.default_profile_fields
if options.delete(:public)
path +=":public"
elsif fields
path +=":(#{fields.map{ |f| f.to_s.gsub("_","-") }.join(',')})"
end
headers = options.delete(:headers) || {}
params = options.map { |k,v| v.is_a?(Array) ? v.map{|i| "#{k}=#{i}"}.join("&") : "#{k}=#{v}" }.join("&")
path += "?#{params}" if not params.empty?
temp_var = get(path, headers)
hash = JSON.parse(temp_var)
conn = hash["numConnections"]
end
As Samy said in a comment:
In Ruby, the last statement will be returned.
So if we take a look at get_person_connections, we see that the last line is self. What it means is that it returns the instance on which the method was called, #client in this case.
Additional notes: the solution would be to remove self, although if the method is used elsewhere be careful as returning self is often used to allow chaining of methods (though it hardly makes sense to do that on a get method).
I am creating an import feature that imports CSV files into several tables. I made a module called CsvParser which parses a CSV file and creates records. My models that receive the create actions extends theCsvParser. They make a call to CsvParser.create and pass the correct attribute order and an optional lambda called value_parser. This lambda transforms values in a hash to a preffered format.
class Mutation < ActiveRecord::Base
extend CsvParser
def self.import_csv(csv_file)
attribute_order = %w[reg_nr receipt_date reference_number book_date is_credit sum balance description]
value_parser = lambda do |h|
h["is_credit"] = ((h["is_credit"] == 'B') if h["is_credit"].present?)
h["sum"] = -1 * h["sum"].to_f unless h["is_credit"]
return [h]
end
CsvParser.create(csv_file, self, attribute_order, value_parser)
end
end
The reason that I'm using a lambda instead of checks inside the CsvParser.create method is because the lambda is like a business rule that belongs to this model.
My question is how i should test this lambda. Should i test it in the model or the CsvParser? Should i test the lambda itself or the result of an array of the self.import method? Maybe i should make another code structure?
My CsvParser looks as follows:
require "csv"
module CsvParser
def self.create(csv_file, klass, attribute_order, value_parser = nil)
parsed_csv = CSV.parse(csv_file, col_sep: "|")
records = []
ActiveRecord::Base.transaction do
parsed_csv.each do |row|
record = Hash.new {|h, k| h[k] = []}
row.each_with_index do |value, index|
record[attribute_order[index]] = value
end
if value_parser.blank?
records << klass.create(record)
else
value_parser.call(record).each do |parsed_record|
records << klass.create(parsed_record)
end
end
end
end
return records
end
end
I'm testing the module itself:
require 'spec_helper'
describe CsvParser do
it "should create relations" do
file = File.new(Rails.root.join('spec/fixtures/files/importrelaties.txt'))
Relation.should_receive(:create).at_least(:once)
Relation.import_csv(file).should be_kind_of Array
end
it "should create mutations" do
file = File.new(Rails.root.join('spec/fixtures/files/importmutaties.txt'))
Mutation.should_receive(:create).at_least(:once)
Mutation.import_csv(file).should be_kind_of Array
end
it "should create strategies" do
file = File.new(Rails.root.join('spec/fixtures/files/importplan.txt'))
Strategy.should_receive(:create).at_least(:once)
Strategy.import_csv(file).should be_kind_of Array
end
it "should create reservations" do
file = File.new(Rails.root.join('spec/fixtures/files/importreservering.txt'))
Reservation.should_receive(:create).at_least(:once)
Reservation.import_csv(file).should be_kind_of Array
end
end
Some interesting questions. A couple of notes:
You probably shouldn't have a return within the lambda. Just make the last statement [h].
If I understand the code correctly, the first and second lines of your lambda are overcomplicated. Reduce them to make them more readable and easier to refactor:
h["is_credit"] = (h['is_credit'] == 'B') # I *think* that will do the same
h['sum'] = h['sum'].to_f # Your original code would have left this a string
h['sum'] *= -1 unless h['is_credit']
It looks like your lambda doesn't depend on anything external (aside from h), so I would test it separately. You could even make it a constant:
class Mutation < ActiveRecord::Base
extend CsvParser # <== See point 5 below
PARSE_CREDIT_AND_SUM = lambda do |h|
h["is_credit"] = (h['is_credit'] == 'B')
h['sum'] = h['sum'].to_f
h['sum'] *= -1 unless h['is_credit']
[h]
end
Without knowing the rationale, it's hard to say where you should put this code. My gut instinct is that it is not the job of the CSV parser (although a good parser may detect floating point numbers and convert them from strings?) Keep your CSV parser reusable. (Note: Re-reading, I think you've answered this question yourself - it is business logic, tied to the model. Go with your gut!)
Lastly, you are defining and the method CsvParser.create. You don't need to extend CsvParser to get access to it, although if you have other facilities in CsvParser, consider making CsvParser.create a normal module method called something like create_from_csv_file