Parse before storing in MVC

Question

I'm getting started with parsing data and getting some structure from user supplied strings (mostly pulling out digits and city names).

I've run a bit of code in the ruby interpreter, and now I want to use that same code in a web application.

I'm struggling as to where in the code my parsing should be, or how it is structured.

My initial instinct was that it belongs in the model, because it is data logic. For example, does the entry have an integer, does it have two integers, does it have a city name, etc. etc.

However, my model would need to inherit both ActiveRecord, and Parslet (for the parsing), and Ruby apparently doesn't allow multiple inheritance.

My current model is looking like this

#concert model
require 'parslet'
class concert < Parlset::Parser
  attr_accessible :date, :time, :city_id, :band_id, :original_string

   rule(:integer) {match('[0-9]').repeat(1)}
   root(:integer)
end

Really not much there, but I think I'm stuck because I've got the structure wrong and don't know how to connect these two pieces.

I'm trying to store the original string, as well as components of the parsed data.

score 1 · Accepted Answer · answered Jul 11 '11 at 18:33

I think what you want is:

#concert model
require 'parslet'
class concert < ActiveRecord::Base
  before_save :parse_fields
  attr_accessible :date, :time, :city_id, :band_id, :original_string


   rule(:integer) {match('[0-9]').repeat(1)}
   root(:integer)

  private
  def parse_fields
    date = Parlset::Parser.method_on_original_string_to_extract_date
    time = Parlset::Parser.method_on_original_string_to_extract_time
    city_id = Parlset::Parser.method_on_original_string_to_extract_city_id
    band_id = Parlset::Parser.method_on_original_string_to_extract_band_id
  end
end

Seems to somewhat do what I'm looking for, though I'm not exactly sure. I guess it is one solution, and the only response so I'll go with it. — pedalpete, Jul 18 '11 at 23:38

score 1 · Answer 2 · answered Sep 27 '11 at 13:53

It looks to me as though you need several parsers (one for city names, one for digits). I would suggest that you create an informal interface for such parsers, such as

class Parser
  def parse(str) # returning result
  end 
end

Then you would create several Ruby classes that each do a parse task in ./lib.

Then in the model, you'd require all these ruby classes, and put them to the task, lets say in a before_save hook or such.

As the author of parslet, I might add that parsing digits or city names is probably not the sweet spot for parslet. Might want to consider regular expressions there.

Parse before storing in MVC

2 Answers2