Should I store US states as an array or create table columns? - ruby

Question

I have an app that houses product data via a Product model and table. Each product has specific state availability (multiple states) that I will need to filter and/or search by in the future. I am hoping to find someone who can tell me the most efficient way to store this data. As I see it, I have two options.
The first is to simply create 50 columns in my table, titled with each state name and containing a boolean value. I can then simply filter by = "avail in California" if product.ca. While this certainly works, it seems a bit cumbersome, especially when searching for multiple state availability.
The second option would be to simply have one column("states") that stores an array of available states and then filter by = "avail in California" if product.states.include? "CA". This seems like a better solution for two reasons. The first, it just allows for a cleaner DB table. Second, and more important, I can allow my user to search by simply saving the user's input as a variable(user_input) and then = "avail in California" if product.states.include? user_input. This solution does call for a little more work up front however when saving the product in the DB, since I won't be able to simply check off a boolean value.
I think option two makes the most sense, but am hoping for some advice as to why or why not. I have found a few similar questions, but they do not seem to explain which solution would be better, just how to accomplish each.
What should I do?

Answer 1

You should normalize unless you have a really good reason not to, and I don't see one in your overview.
To normalize, you should have the following tables:
product table, one record per product
state table, one record per state
product_state table, one entry for every product that is in a state
The product_state schema looks like this:
(product_state_id PK, product_id FK, state_id FK)
UNIQUE INDEX(product_id,state_id);
This allows you to have a product in zero or more states.

Answer 2

I assume that since you’re selling products, you will be charging taxes. There are different taxes by state, county, city. There are country taxes in some countries too.
So you need to abstract these entities into a common parent, usually called GeopoliticalArea, so that you can point a single foreign key (from, say, a tax rates table) at any subtype.
create table geopolitical_area (
id bigint primary key,
type text not null
);
create table country (
id bigint primary key references geopolitical_area(id),
name text not null unique
);
-- represents states/provinces:
create table region (
id bigint primary key references geopolitical_area(id),
name text not null,
country_id bigint references country(id),
unique (name, country_id)
);
insert into geopolitical_area values
(1, 'Country'),
(2, 'Region');
insert into country values
(1, 'United States of America');
insert into region values
(2, 'Alabama', 1);