ruby coredata access class

coredata.rb

require 'rubygems'
require 'sqlite3'

class Coredata  
  attr_accessor :db
  
  def initialize(app_name)
    pattern = File.join("#{ENV['HOME']}",
                        "/Library/Application Support/iPhone Simulator/*",
                        "/Applications/*/Documents/#{app_name}.sqlite")
    match_paths = Dir.glob(pattern)
    path = match_paths.size == 1 ? match_paths.first : nil
    
    raise "Database '#{pattern}' not found." until path
    
    @db = SQLite3::Database.new(path)
  end
  
  def close
    db.close
  end
  
  def count(entity_name)
    sql = "SELECT COUNT(*) FROM #{table_name(entity_name)}"
    db.execute(sql).first.first
  end
  
  def insert(entity_name, params = {})
    fields = params.keys.map { |key| "z#{key}" }.join(', ')
    placeholder = params.keys.map { |key| '?' }.join(', ')
    sql = "INSERT INTO #{table_name(entity_name)} (Z_ENT, Z_OPT, #{fields}) VALUES (?, ?, #{placeholder})"
    
    values = [1, 1]
    values << params.values.map do |value|
      value.respond_to?(:strftime) ? value.to_i - 978328800 : value
    end
    
    db.execute(sql, values)
  end
  
  def delete_all(entity_name)
    sql = "DELETE FROM #{table_name(entity_name)}"
    db.execute(sql)
  end
  
private
  def table_name(entity_name)
    "Z#{entity_name.upcase}"
  end
end