patient.rb

class Patient
  include Mongoid::Document

  field :created_at,          type: Time
  field :updated_at,          type: Time

  def self.group_by(field, format = 'day')
    reduce = %Q{
      function(key, values) {
        var result = { count: 0 };
        values.forEach(function(value) {
          result.count += value.count;
        });
        return result;
      }
    }

    Patient.map_reduce(Patient.map(field, format), reduce).out(inline: true)
  end

  def self.map(date_field, format = 'day')
    date_format = case format
    when 'month'
      "mm + '/' + yyyy"
    when 'year'
      "yyyy"
    else
      "dd + '/' + mm + '/' + yyyy"
    end

    %Q{
      function() {
        var dateTime  = new Date(this.#{date_field});
        var dd        = dateTime.getDate();
        var mm        = dateTime.getMonth() + 1;
        var yyyy      = dateTime.getFullYear();

        var date = #{date_format};

        emit(date, { count: 1 });
      }
    }
  end
end