Using scope to return results within multiple DateTime ranges in ActiveRecord

Question

I've got a Session model that has a :created_at date and a :start_time date, both stored in the database as :time. I'm currently spitting out a bunch of results on an enormous table and allowing users to filter results by a single date and an optional range of time using scopes, like so:

class Session < ActiveRecord::Base
  ...

  scope :filter_by_date, lambda { |date|
    date = date.split(",")[0]
    where(:created_at =>
      DateTime.strptime(date, '%m/%d/%Y')..DateTime.strptime(date, '%m/%d/%Y').end_of_day
    )
  }
  scope :filter_by_time, lambda { |date, time|
    to = time[:to]
    from = time[:from]
    where(:start_time =>
      DateTime.strptime("#{date} #{from[:digits]} #{from[:meridian]}", '%m/%d/%Y %r')..
      DateTime.strptime("#{date} #{to[:digits]} #{to[:meridian]}", '%m/%d/%Y %r')
    )
  }

end

The controller looks more or less like this:

class SessionController < ApplicationController

  def index
    if params.include?(:date) ||
       params.include?(:time) &&
     ( params[:time][:from][:digits].present? && params[:time][:to][:digits].present? )

      i = Session.scoped
      i = i.filter_by_date(params[:date]) unless params[:date].blank?
      i = i.filter_by_time(params[:date], params[:time]) unless params[:time].blank? || params[:time][:from][:digits].blank? || params[:time][:to][:digits].blank?

      @items = i
      @items.sort_by! &params[:sort].to_sym if params[:sort].present?
    else
      @items = Session.find(:all, :order => :created_at)
    end
  end

end

I need to allow users to filter results using multiple dates. I'm receiving the params as a comma-separated list in string format, e.g. "07/12/2012,07/13/2012,07/17/2012", and need to be able to query the database for several different date ranges, and time ranges within those date ranges, and merge those results, so for example all of the sessions on 7/12, 7/13 and 7/17 between 6:30 pm and 7:30 pm.

I have been looking everywhere and have tried several different things but I can't figure out how to actually do this. Is this possible using scopes? If not what's the best way to do this?

My closest guess looks like this but it's not returning anything so I know it's wrong.

scope :filter_by_date, lambda { |date|
  date = date.split(",")
  date.each do |i|
    where(:created_at =>
      DateTime.strptime(i, '%m/%d/%Y')..DateTime.strptime(i, '%m/%d/%Y').end_of_day
    )
  end
}
scope :filter_by_time, lambda { |date, time|
  date = date.split(",")
  to = time[:to]
  from = time[:from]
  date.each do |i|
    where(:start_time =>
      DateTime.strptime("#{i} #{from[:digits]} #{from[:meridian]}", '%m/%d/%Y %r')..
      DateTime.strptime("#{i} #{to[:digits]} #{to[:meridian]}", '%m/%d/%Y %r')
    )
  end
}

Another complication is that the start times are all stored as DateTime objects so they already include a fixed date, so if I want to return all sessions started between 6:30 pm and 7:30 pm on any date I need to figure something else out too. A third party is responsible for the data so I can't change how it's structured or stored, I just need to figure out how to do all these complex queries. Please help!

---

EDIT:

Here's the solution I've come up with by combining the advice of Kenichi and Chuck Vose below:

scope :filter_by_date, lambda { |dates|
  clauses = []
  args = []
  dates.split(',').each do |date|
    m, d, y = date.split '/'
    b = "#{y}-#{m}-#{d} 00:00:00"
    e = "#{y}-#{m}-#{d} 23:59:59"
    clauses << '(created_at >= ? AND created_at <= ?)'
    args.push b, e
  end
  where clauses.join(' OR '), *args
}

scope :filter_by_time, lambda { |times|
  args = []
  [times[:from], times[:to]].each do |time|
    h, m, s = time[:digits].split(':')
    h = (h.to_i + 12).to_s if time[:meridian] == 'pm'
    h = '0' + h if h.length == 1
    s = '00' if s.nil?
    args.push "#{h}:#{m}:#{s}"
  end
  where("CAST(start_time AS TIME) >= ? AND
         CAST(start_time AS TIME) <= ?", *args)
}

This solution allows me to return sessions from multiple non-consecutive dates OR return any sessions within a range of time without relying on dates at all, OR combine the two scopes to filter by non-consecutive dates and times within those dates. Yay!

An important point I overlooked is that the where statement must come last -- keeping it inside of an each loop returns nothing. Thanks to both of you for all your help! I feel smarter now.

Answer 1

something like:

scope :filter_by_date, lambda { |dates|
  clauses = []
  args = []
  dates.split(',').each do |date|
    m, d, y = date.split '/'
    b = "#{y}-#{m}-#{d} 00:00:00"
    e = "#{y}-#{m}-#{d} 23:59:59"
    clauses << '(start_time >= ? AND start_time <= ?)'
    args.push b, e
  end
  where clauses.join(' OR '), *args
}

and

scope :filter_by_time, lambda { |dates, time|
  clauses = []
  args = []
  dates.split(',').each do |date|
    m, d, y = date.split '/'
    f = time[:from] # convert to '%H:%M:%S'
    t = time[:to]   # again, same
    b = "#{y}-#{m}-#{d} #{f}"
    e = "#{y}-#{m}-#{d} #{t}"
    clauses << '(start_time >= ? AND start_time <= ?)'
    args.push b, e
  end
  where clauses.join(' OR '), *args
}

Answer 2

So, the easy part of the question is what to do about datetimes. The nice thing about DateTimes is that they can be cast to times really easily with this:

CAST(datetime_col AS TIME)

So you can do things like:

i.where("CAST(start_time AS TIME) IN(?)", times.join(", "))

Now, the harder part, why aren't you getting any results. The first thing to try is to use i.to_sql to decide whether the scoped query looks reasonable. My guess is that when you print it out you'll find that all those where are chaining together with AND. So you're asking for objects with a date that is on 7/12, 7/13, and 7/21.

The last part here is that you've got a couple things that are concerning: sql injections and some overeager strptimes.

When you do a where you should never use #{} in the query. Even if you know where that input is coming from your coworkers may not. So make sure you're using ? like in the where I did above.

Secondly, strptime is extremely expensive in every language. You shouldn't know this, but it is. If at all possible avoid parsing dates, in this case you can probably just gsub / into - in that date and everything will be happy. MySQL expects dates in m/d/y form anyways. If you're still having trouble with it though and you really need a DateTime object you can just as easily do: Date.new(2001,2,3) without eating your cpu.