Ruby on Rails style database interface for CSV files

csv.rb

class HeaderType
    attr_reader :header
    ATTRS = {string: :string, int: :int, number: :int, integer: :int }
    def initialize
        @header = []
    end
    # Define methods string, integer, etc., 
    # for schema definition dynamically
    class_eval do
        ATTRS.each do |attr, type|
            define_method attr do |name|
                @header << [type, name]
            end
        end
    end
end

class CSV
    def self.create_table(name, &block)
       # Generate the appropriate class for the schema
       dync = Class.new do |k|
        @@db     = nil
        @@table  = []
        @@header = []
        @@rows   = []

        define_method :initialize do |row|
            @new_row = row
            row.each do |k,e|
                define_singleton_method k do return @new_row[k] end 
            end
        end

        define_method :save do
            return false if @new_row.empty? or @new_row.nil?
            @@header.each do |t,e|
                return false if (@new_row[e.to_sym] == nil)
            end
            @@rows << @new_row.values
            @@table << @new_row
            return true
        end

        define_singleton_method :create do |args|
           k.new(args) 
        end

        define_singleton_method :pretty_print do
            max = []
            @@rows.each_with_index do |row, i|
                max[i] = 0
                row.map do |col|
                    len = col.to_s.length 
                    max[i] = len if (len > max[i])
                end
                max[i] += 2
            end

            sep_line = '+'
            @@header.each_index do |i|
                sep_line += ('-' * max[i]) + '+'
            end
            @@rows.each do |row|
                puts sep_line
                row.each_with_index do |c,i|
                    printf("| %-#{max[i]-2}s ", c)
                end
                puts '|'
            end
            puts sep_line
        end

        define_singleton_method :find do |col, e|
           arr = []
           @@table.each do |r|
               arr << r if (r[col] == e)
           end
           return nil if arr.empty?
           return arr
        end

        define_singleton_method :all do
          return @@table
        end

        define_singleton_method :all_rows do
          return @@rows
        end

        define_singleton_method :read_file do |fname|
           if @@db.nil? 
               @@db = File.open(fname, 'r');
           end
           @@db.readline
           @@db.each_line do |l|
            r = l.chomp.split(/,/)
            rh = {}
            rl = []
            @@header.each_with_index do |h,i|
                if h[0] == :int
                    e = r[i].to_i
                else
                    # remove the leading and closing quotes
                    if (r[i][0] == '"' and r[i][-1] == '"')
                        e = r[i][1..(-2)]
                    else
                        e = r[i]
                    end
                end
                rh[h[1]] = e
                rl << e
            end
            @@rows << rl
            @@table << rh
           end
           @@db.close
        end

        define_singleton_method :set_header do |hdr|
            @@header = hdr
        end
       end
       klass = Object.const_set(name.capitalize, dync)
       h = HeaderType.new
       block.call(h) 
       hdr = h.header
       klass.set_header hdr
       klass.read_file "#{name}.csv"
    end
end
#
# END OF THE IMPLEMENTATION #
# Define csv schema for a person
# NOTICE: A person.csv file is mandatory
CSV.create_table 'person' do |t|
    t.string :fname
    t.string :sname
    t.int :birth_year
    t.int :postcode
end

puts "--- List all persons in the file ---"
puts Person.all # list all person from file
puts "--- Find someone from 1990 ---"
puts Person.find(:birth_year, 1990) # find
puts "--- Create a new person ---"
p = Person.create(fname: 'John', sname: 'Doe', birth_year: 1991, postcode: 2092)
puts p.inspect
puts "--- Save '#{p.fname} #{p.sname}' to the database ---"
p.save
puts "--- Pretty print the new table ---"
puts Person.pretty_print