how to store work schedule information using a bitmask?

Question

creating a very simple scheduling app

I am asking the user to tell me what day(s) they work, and whether on a given day they work morning, lunch, or evening

so, for a given user her data could be one or all of the points in the following matrix

        morning    lunch    evening
mon
tue
wed
thr
fri
sat
sun 

I need to quickly be able to retrieve this information so that I can alert the user that it's time to go to work. I will have many users.

I don't care about specific dates, or time. just the discrete days 1 through 7 and the 3 slots within each day. Certainly, there are many possible combinations.

I am considering how to store this information. And I am wondering if a bitmask is appropriate / feasible / the 'way to go with something like this' ? How would you approach this?

thanks!

Answer 1

While a bitmask will definitely work (employing 7 days X 3 shifts = 21 bits), my experience with these things is they always need modification. That is, a night shift is added, or shifts are otherwise changed.

Given that, I'd suggest building some flexibility into your app. Combine the bitmask idea with a table that defines what the bits represent. That way you can redefine and modify as you please. If you add a shift, just add a record to the definition table and update each employee's mask.

Answer 2

To answer your second question: unless you have millions of rows, a bitmask is not going to be a huge performance advantage (your bottleneck will still be network I/O) and probably a premature optimization. That said, you will be able to store all of the user's options in a single 32 bit integer.

Answer 3

Don't bother with a bitmask. Do something simple now (like perhaps a normalized DB schema!), and optimize for performance later if you start measuring problems.

Answer 4

If they can only choose one option per day, you can pack the data into 14 bits of a 16-bit int. Or if they can choose multiple options per day, you could pack it into 21 bits of a 32-bit int.