How would you build this daily class schedule?

Question

What I want to do is very simple but I'm trying to find the best or most elegant way to do this. The Rails application I'm building now will have a schedule of daily classes. For each class the fields relevant to this question are:

• Day of the week
• Starting time
• Ending time

A single entry could be something such as:

• day of week: Wednesday
• starting time: 10:00 am
• ending time: Noon

Also I must mention that it's a bi-lingual Rails 2.2 app and I'm using the native i18n Rails feature. I actually have several questions.

Regarding the day of the week, should I create an extra table with list of days, or is there a built-in way to create that list on the fly? Keep in mind these days of the week will have to be rendered in English or Spanish in the schedule view depending on the locale variable.

While querying the schedule I will need to group and order the results by weekday, from Monday to Sunday, and of course order the classes within each day by starting time.

Regarding the starting time and ending time of each class would you use datetime fields or integer fields? If the latter how would you implement this exactly?

Looking forward to read the different suggestions you guys will come up with.

Answer 1

If your data is a Time then I would store that as a Time - otherwise you will always have to convert it out of the database when you do date and time related operations on it. The day is redundant data, as it will be part of the time object.

This should mean that you don't need to store a list of days.

If t is a time then

t.strftime('%A')

will always give you the day as a string in English. This could then be translated by i18n as required.

So you only need to store starting time and ending time, or starting time and duration. Both should be equivalent. I would be tempted to store ending time myself, in case you need to do data manipulations on ending times, which therefore won't have to be calculated.

I think most of the rest of what you describe should also fall out of storing time data as instances of Time.

Ordering by week day and time will just be a matter of ordering by your time column. i.e.

daily_class.find(:all, :conditions => ['whatever'], :order => :starting_time)

Grouping by day is a little more tricky. However this is an excellent post on how to group by week. Grouping by day will be analogous.

If you are dealing with non-trivial volumes of data, it may be better to do it in the database, with a find_by_sql and that may depend on your database's time and date functionality, but again storing the data as a Time will also help you here. For example in Postgresql (which I use), getting the week of a class is

date_trunc('week', starting_time)

which you can use in a Group By clause, or as a value to use in some loop logic in rails.

Answer 2

Re days-of-week, if you need to have e.g. classes that meet 09:00-10:00 on MWF, then you could either use a separate table for days a class meets (keyed by both class ID and DOW) or be evil (i.e. non-normalized) and keep the equivalent of an array of DOW in each class. The classic argument is this:

• The separate table can be indexed in a way to support either class-oriented or DOW-oriented selects, but takes a bit more glue to put the entire picture together for a class.
• The array-of-DOW is simpler to visualize for beginning programmers and slightly simpler to code about, but means that reasoning about DOW requires looking at all classes.

If this is only for your personal class schedule, do what gets you the value you're looking for, and live with the consequences; if you're trying to build a real system for multiple users, I'd go with a separate table. All those normalization rules are there for a reason.

As far as (human-readable) DOW names, that's a presentation-layer issue, and shouldn't be in the core concept of DOW. (Suppose you decided to move to Montreal, and needed French? That should be another "face" and not a change to the core implementation.)

As for starting/ending times, again the issue is your requirements. If all classes begin and end at hour (x:00) boundaries, you could certainly use 0..23 as the hours of the day. But then your life would be miserable as soon as you had to accommodate that 45-minute seminar. As the old commercial said, "Pay me now or pay me later."

One approach would be to define your own ClassTime concept and partition all reasoning about times to that class. It could start with a simplistic representation (integral hours 0..23, or integral minutes after midnight 0..1439) and then "grow" as needed.

Answer 3

I would just store the day of the week as an integer. 0 => Monday ... 6 => Sunday (or any way you want. ie. 0 => Sunday). Then store the start time and end time as Time.

That would make grouping really easy. All you would have to do is sort by the day of the week and the start time.

You can display this in multiple ways, but here is what I would do.

1. Have functions like: @sunday_classes = DailyClass.find_sunday_classes that returns all the classes for Sunday sorted by start time. Then repeat for each day.

   def find_sunday_classes
     find_by_day_of_week(1, :order -> 'start_time')
   end

   Note: find_by probably should have id at the end but that's just preference in how you want to name the column.

2. If you want the full week then call all seven from the controller and loop trough them in the view. You could even create detail pages for each day.

3. Translation is the only tricky part. You can create a helper function that takes an integer and returns the text for the appropriate day of the week based on local.

That's very basic. Nothing complicated.