SQLAlchemy 计算列和排序

Question

I want to calculate the distance from the input zip code and the zip code stored in the database and sort them in order of distance.

I have a 'getdistance' function that calculates the distance from two zip codes using pgeocode. I would like to implement the following

neighbor = database.query(DataBase).order_by(getdistance(input_zipcode, Database.zipcode))

Is this possible using sqlalchemy?

Answer 1

It is not possible if you are using a db engine like MySQL or PostgreSQL, as the order_by feature is used to build a SQL statement run by the database engine which would have no ability to use the pgeocode python library.

You do have some options though. If you are always querying all results, you can do this, which loads all of the rows and then sorts them using Python:

neighbor = list(sorted(
  database.query(DataBase).all(), 
  key=lambda d: getdistance(input_zipcode, d.zipcode)
)

My guess is this would be performant enough for your needs after maybe 10,000 records or so.

Otherwise, you will need to find a way for your database engine to calculate the distance-based-on-zip-code (stored procedures, table lookups, GIS extensions, etc).

If you do happen to be using SQLite, then you COULD actually register a custom function for SQLite to call, allowing an order_by clause to work (but the performance should not be drastically different than the above solution).