Database Design for state, cities and districts - ruby-on-rails

Question

I have users represented in a user table and need to design a model to associate them with state/cities/districts that they choose:
On the database side,
Each user will be associated with 1 state, 1 city and a number of districts within that state/city combination. For instance, User A can choose to be associated with "NY" and "Brooklyn" and any X number of districts in "Brooklyn" (or none).
On the view side,
I'd like to present the district choices with checkboxes so they should be able to be pulled from the database field with simple_form in Rails pretty easily.
The design of the database should make it easy to query for the user and get the associated state / city and district relations that the user has chosen.
One idea I have is to simply have a one-to-many field for districts and a district table listing all the different districts. However, is there a way to enforce that the districts have to be valid for the city/state combination on the backend using validate?
Any tips would be appreciated.

Answer 1

Below I have outlined the database schema I would use based on the information you have given.
Every city belongs to exactly one state.
cities
id unsigned int(P)
state_id unsigned int(F states.id)
name varchar(50)
+----+----------+---------------+
| id | state_id | name |
+----+----------+---------------+
| 1 | 33 | New York City |
| .. | ........ | ............. |
+----+----------+---------------+
See ISO 3166 for more information. You didn't ask for countries but it's trivial to add them...
countries
id char(2)(P)
iso3 char(3)(U)
iso_num char(3)(U)
name varchar(45)(U)
+----+------+---------+---------------+
| id | iso3 | iso_num | name |
+----+------+---------+---------------+
| ca | can | 124 | Canada |
| mx | mex | 484 | Mexico |
| us | usa | 840 | United States |
| .. | .... | ....... | ............. |
+----+------+---------+---------------+
Every district belongs to exactly one city.
districts
id unsigned int(P)
city_id unsigned int(F cities.id)
name varchar(50)
+----+---------+-----------+
| id | city_id | name |
+----+---------+-----------+
| 1 | 1 | The Bronx |
| 2 | 1 | Brooklyn |
| 3 | 1 | Manhattan |
| .. | ....... | ......... |
+----+---------+-----------+
See ISO 3166-2:US for more information. Every state belongs to exactly one country.
states
id unsigned int(P)
country_id char(2)(F countries.id)
code char(2)
name varchar(50)
+----+------------+------+----------+
| id | country_id | code | name |
+----+------------+------+----------+
| 1 | us | AL | Alabama |
| .. | .......... | .... | ........ |
| 33 | us | NY | New York |
| .. | .......... | .... | ........ |
+----+------------+------+----------+
Based on your information a user belongs to exactly one city. In the example data Bob is associated with New York City. By joining tables you can very easily find that Bob is in New York state and the country of United States.
users
id unsigned int(P)
username varchar(255)
city_id unsigned int(F cities.id)
...
+----+----------+---------+-----+
| id | username | city_id | ... |
+----+----------+---------+-----+
| 1 | bob | 1 | ... |
| .. | ........ | ....... | ... |
+----+----------+---------+-----+
Users can belong to any number of districts. In the example data Bob belongs to The Bronx and Brooklyn. user_id and district_id form the Primary Key which insures a user cannot be associated with the same district more than once.
users_districts
user_id unsigned int(F users.id) \_(P)
district_id unsigned int(F districts.id) /
+---------+-------------+
| user_id | district_id |
+---------+-------------+
| 1 | 1 |
| 1 | 2 |
| ....... | ........... |
+---------+-------------+
My database model does NOT enforce the rule that the districts a user belongs to must be in the city that user belongs to - in my opinion that logic should be done at the application level. If Bob moves from New York City to Baltimore I think all of his records should be deleted from the users_districts table and then add any new ones for his new city.
As for the user interface, I would have the user:
Select a country - this will auto-populate a drop down list of associated states.
Select a state - this will auto-populate a drop down list of associated cities.
Select a city - this will auto-populate a list of associated districts.
Allow the user to select any number of districts.

Answer 2

You will need some combination of database and application-level logic.
Here is how I would build the database fields:
users = id, <other user fields>, city_id
districts = id, <other district fields>, city_id
cities = id, name, state_id
states = id, name
And then in the application, set it up so that the user can type in one city and multiple districts, and can not edit the state (view only):
When the user types in a city - maybe through a autocomplete field - it automatically updates the read-only state field with the state of the city
When the user types in a district, list only the districts that have district.city_id == cities.id
If you don't want to restrict the district selection in the UI, you will need to enforce the district.city_id == cities.id check in your application, though I personally think that's less intuitive than doing it right in the front-end UI.

Answer 3

Indian States AND UT MySQL QUERY
INSERT INTO `states`
VALUES
(1,'Andhra Pradesh'),
(2,'Telangana'),
(3,'Arunachal Pradesh'),
(4,'Assam'),
(5,'Bihar'),
(6,'Chhattisgarh'),
(7,'Chandigarh'),
(8,'Dadra and Nagar Haveli'),
(9,'Daman and Diu'),
(10,'Delhi'),
(11'Goa'),
(12,'Gujarat'),
(13,'Haryana'),
(14,'Himachal Pradesh'),
(15,'Jammu and Kashmir'),
(16,'Jharkhand'),
(17,'Karnataka'),
(18,'Kerala'),
(19,'Madhya Pradesh'),
(20,'Maharashtra'),
(21,'Manipur'),
(22,'Meghalaya'),
(23,'Mizoram'),
(24,'Nagaland'),
(25,'Orissa'),
(26,'Punjab'),
(27,'Pondicherry'),
(28,'Rajasthan'),
(29,'Sikkim'),
(30,'Tamil Nadu'),
(31,'Tripura'),
(32,'Uttar Pradesh'),
(33,'Uttarakhand'),
(34,'West Bengal'),
(35,'Lakshadweep'),
(36,'Ladakh ');