define_method: How to dynamically create methods with arguments

Question

I want to create a bunch of methods for a find_by feature. I don't want to write the same thing over and over again so I want to use metaprogramming.

Say I want to create a method for finding by name, accepting the name as an argument. How would I do it? I've used define_method in the past but I didn't have any arguments for the method to take. Here's my (bad) approach

["name", "brand"].each do |attribute|     define_method("self.find_by_#{attribute}") do |attr_|       all.each do |prod|         return prod if prod.attr_ == attr_       end     end   end 

Any thoughts? Thanks in advance.

Answer 1

If I understand your question correctly, you want something like this:

class Product   class << self     [:name, :brand].each do |attribute|       define_method :"find_by_#{attribute}" do |value|         all.find {|prod| prod.public_send(attribute) == value }       end     end   end end 

(I'm assuming that the all method returns an Enumerable.)

The above is more-or-less equivalent to defining two class methods like this:

class Product   def self.find_by_name(value)     all.find {|prod| prod.name == value }   end    def self.find_by_brand(value)     all.find {|prod| prod.brand == value }   end end 

Answer 2

It if you read the examples here http://apidock.com/ruby/Module/define_method you will find this one:

define_method(:my_method) do |foo, bar| # or even |*args|   # do something end 

is the same as

def my_method(foo, bar)    # do something end