I have two methods that are identical apart from the ActiveRecord class they are referencing:
def category_id_find(category_name)
category = Category.find_by_name(category_name)
if category != nil
return category.id
else
return nil
end
end
def brand_id_find(brand)
brand = Brand.find_by_name(brand)
if brand != nil
return brand.id
else
return nil
end
end
Now, I just know there must be a more Railsy/Ruby way to combine this into some kind of dynamically-created method that takes two arguments, the class and the string to find, so I tried (and failed) with something like this:
def id_find(class, to_find)
thing = (class.capitalize).find_by_name(to_find)
if thing.id != nil
return thing.id
else
return nil
end
end
which means I could call id_find(category, "Sports")
I am having to populate tables during seeding from a single, monster CSV file which contains all the data. So, for example, I am having to grab all the distinct categories from the CSV, punt them in a Category table then then assign each item's category_id based on the id from the just-populated category table, if that makes sense...
class is a reserved keyword in Ruby (it's used for class declarations only), so you can't use it to name your method parameter. Developers often change it to klass, which preserves the original meaning without colliding with this restriction. However, in this case, you'll probably be passing in the name of a class as a string, so I would call it class_name.
Rails' ActiveSupport has a number of built in inflection methods that you can use to turn a string into a constant. Depending on what your CSV data looks like, you might end up with something like this:
def id_find(class_name, to_find)
thing = (class_name.camelize.constantize).find_by_name(to_find)
...
end
If using a string, you can use constantize instead of capitalize and your code should work (in theory):
thing = passed_in_class.constantize.find_by_name(to_find)
But you can also pass the actual class itself to the method, no reason not to:
thing = passed_in_class.find_by_name(to_find)
Related
I have created a small Ruby class here:
class Star
#Star initialization
def initialize(star, number)
#star = star
#number = number
end
end
and I am looking to initialize a class called Solar System with 100 stars. This is what I have done and it doesn't seem to be working. Any help would be greatly appreciated.
require_relative 'star.rb'
class SolarSystem
#Initialize Game
def initialize(partOfSolarSystem)
#partOfSolarSystem = partOfSolarSystem
#stars_array = []
for i in 0..99
stars_array = Star.new('unknown_star',i)
end
end
def show_solar_system
#code here to show all the initialized stars in solar system
end
end
I can't seem to get it to initialize the array in the constructor. I would then like to be able to print out all of the elements in the stars array. Any help with this would be greatly appreciated.
Also in an effort to eventually move this to a database with rails or something of that nature, should I be looking to hash this or will this be easily converted to mySQL or another DB with some helper functions? I would eventually like to write this into rails and have a dynamic website for it.
Once again, thanks very much.
Your problem is assigning a new value to #stars_array variable on each iteration. There are multiple ways to deal with it:
#stars_array = (0..99).map { |i| Star.new('unknown_star',i) }
By the way, there is a couple of design issues (just for your attention):
Why variable is called stars_array, not just stars?
Why would ever instance of Star class have some object named #star inside? Recursion? :) Seems like #name would be proper and more clear attribute's name.
Don't miss indentation.
EDIT: About DB-mapping. Most common way - inherit both classes from ActiveRecord::Base, and create one-to-many relation from solar system to stars. Each class will have it's own table. Takes absolutely no efforts.
You are assigning the new object every time round the loop. The fix is to append the new object:
#stars_array << Star.new('unknown_star',i)
Or, if you prefer words rather than symbols:
#stars_array.push(Star.new('unknown_star',i))
Or, to be more terse:
100.times {|i| #stars_array << Star.new('unknown_star',i) }
A few things to fix to make it work. In your loop you're assigning a new value to the array rather than appending to it. Secondly, in your loop you're using a local variable stars_array instead of the instance variable #stars_array.
Your initialize method should look like this:
def initialize(part_of_solar_system)
#part_of_solar_system = part_of_solar_system
#stars_array = []
for i in 0..99
#stars_array << Star.new('unknown_star', i)
end
end
Also, you might want to revisit your Ruby idioms, like preferring snake_case to camelCase for variable names and avoiding for loops in favor of each, e.g.
def initialize(part_of_solar_system)
#part_of_solar_system = part_of_solar_system
#stars_array = []
(0..99).each { |i| #stars_array << Star.new('unknown_star', i) }
end
In my rails3.1 application, I'm trying to apply the following logic in one of my order model.
def digital?
line_items.map { |line_item| return false unless line_item.variant_id = '102586070' }
end
I've created a separate variant called prepaid_voucher which has id = 102586070. Despite this, the result is false...
Order has many line_items
LineItem belongs to order and variant
Variant has many line_items
Is this the best way to perform such a task and how can I fix?
First of all I think you want a double == here line_item.variant_id = '102586070', then I rather go for something like that (If I understand what you want)
def digital?
line_items.select{|line_item| line_item.variant_id == '102586070'}.any?
end
But it's hard to understand what you really want, what is the expected behavior if the id is not found?
In a rails application, I have a number of attributes for a model called Record. I want to design a method that when called on an attribute, returns the name of the attribute (which is essentially a method on the Record object). This name is then passed to an Hash, which returns a number (for the sake of this example, say the number is a percentage which is then multiplied by the original attribute value to get a new value).
For example, say my Record has four attributes: teachers, students, principals, and parents. The method would then look like the following:
def name
**something here**
end
and the corresponding new_value method and PRECENTAGE hash would look like this:
def new_value
self * PERCENTAGE[self.name]
end
PERCENTAGE = {
"teachers" => 0.40,
"students" => 0.53,
"principals" => 0.21,
"parents" => 0.87
}
Then, to execute this whole thing, I would do Record.students.new_value, which would return new number of students according to the percentage obtained in the hash.
I know that to get the name of a method that is currently executing, you can do something like this: (found on http://ryat.la/7RDk)
def this_method
__method__
end
but that won't work for me, because I need the name of the previously executed method.
If you have any suggestions as to an alternative approach to accomplishing my goal, I'd be happy to try something else.
Ryan, I'm struggling to understand your question, but I think this is what you want, for record.teachers_percent, for example:
["teachers", "students", "principals", "parents"].each do |attrib|
Record.class_eval <<-RUBY
def #{attrib}_percent
#{attrib} * PERCENTAGE[#{attrib.inspect}]
end
RUBY
end
Although this is probably a cleaner solution, giving record.percent(:teachers) or record.percent("teachers"):
class Record
def percent(attrib)
self.send(attrib) * PERCENTAGE[attrib.to_s]
end
end
For single table inheritance, how do you force Rails to use an integer column for the 'type' column instead of string?
You can override the methods Rails uses to convert the table name to class name and vice versa:
The relevant methods are find_sti_class which is responsible for the translating the value stored in the type column to the respective ActiveRecord model and sti_name which is responsible for retriving the value stored in type column given an ActiveRecord subclass.
You can override them like this:
class Institution::Base < ActiveRecord::Base
ALLOWED_CLASSES = %w[Institution::NonProfit Institution::Commercial]
class << self
def find_sti_class type_name
idx = type_name.to_i
super if idx == 0
ALLOWED_CLASSES[idx-1].constantize
rescue NameError, TypeError
super
end
def sti_name
idx = ALLOWED_CLASSES.index(self.name)
if idx.nil?
super
else
idx + 1
end
end
end
end
I have written a post elaborating this in more detail.
You would have to find the part of ActiveRecord responsible for handling the "type" column and monkey patch it, i.e. override how it worked from within your application.
I am trying to use a time_select to input a time into a model that will then perform some calculations.
the time_select helper prepares the params that is return so that it can be used in a multi-parameter assignment to an Active Record object.
Something like the following
Parameters: {"commit"=>"Calculate", "authenticity_token"=>"eQ/wixLHfrboPd/Ol5IkhQ4lENpt9vc4j0PcIw0Iy/M=", "calculator"=>{"time(2i)"=>"6", "time(3i)"=>"10", "time(4i)"=>"17", "time(5i)"=>"15", "time(1i)"=>"2009"}}
My question is, what is the best way to use this format in a non-active record model. Also on a side note. What is the meaning of the (5i), (4i) etc.? (Other than the obvious reason to distinguish the different time values, basically why it was named this way)
Thank you
You can create a method in the non active record model as follows
# This will return a Time object from provided hash
def parse_calculator_time(hash)
Time.parse("#{hash['time1i']}-#{hash['time2i']}-#{hash['time3i']} #{hash['time4i']}:#{hash['time5i']}")
end
You can then call the method from the controller action as follows
time_object = YourModel.parse_calculator_time(params[:calculator])
It may not be the best solution, but it is simple to use.
Cheers :)
The letter after the number stands for the type to which you wish it to be cast. In this case, integer. It could also be f for float or s for string.
I just did this myself and the easiest way that I could find was to basically copy/paste the Rails code into my base module (or abstract object).
I copied the following functions verbatim from ActiveRecord::Base
assign_multiparameter_attributes(pairs)
extract_callstack_for_multiparameter_attributes(pairs)
type_cast_attribute_value(multiparameter_name, value)
find_parameter_position(multiparameter_name)
I also have the following methods which call/use them:
def setup_parameters(params = {})
new_params = {}
multi_parameter_attributes = []
params.each do |k,v|
if k.to_s.include?("(")
multi_parameter_attributes << [ k.to_s, v ]
else
new_params[k.to_s] = v
end
end
new_params.merge(assign_multiparameter_attributes(multi_parameter_attributes))
end
# Very simplified version of the ActiveRecord::Base method that handles only dates/times
def execute_callstack_for_multiparameter_attributes(callstack)
attributes = {}
callstack.each do |name, values|
if values.empty?
send(name + '=', nil)
else
value = case values.size
when 2 then t = Time.new; Time.local(t.year, t.month, t.day, values[0], values[min], 0, 0)
when 5 then t = Time.time_with_datetime_fallback(:local, *values)
when 3 then Date.new(*values)
else nil
end
attributes[name.to_s] = value
end
end
attributes
end
If you find a better solution, please let me know :-)