Drill down filtering query in linq c#

Question

I've been having a problem involving filtering down a list based on 3 different types of list sources.

Suppose I have a very large list encompassing every hospital in the US. So I have 3 tables, a State table showing all hospitals for each state, a Cities table where I show all hosptials in Cities of each state, and a ZipCode table where I show all hospitals within a zipcode.

Here are a few scenarios of my search:

• If I search on 2 states, NY and CA, I get a list of all the hospitals in those states.
• If I add a a few cities, New York and Las Angeles, then the filter is zoomed down to those hospitals.
• If I include a zipcode regardless of states or cities, like a zipcode in Alaska, then I show those (it still shows the hospitals selected for NYC, NY and Las Angeles, CA).

here's what I have so far:

(from hospitals in context.Hospitals)
 where HospitalIDsByState.Contains(hospitals.state) &&
       HospitalIDsByCity.Contains(hosptials.city) ||
       HospitalIDsByZipcodes(hospitals.zipcode)
 select hospitals)

• HospitalIDsByState a list of IDs from a previous query filtered on selected states
• HospitalIDsByCity is a list of IDs from a query filtered on selected cities
• HospitalIDsByZipcodes is a list of IDs from a query filtered on selected zipcodes

the problem I have here is that if I selected States but my Cities is empty, I don't get any results, I need it to be filtered where if only States are selected, I can get a list, if Cities are selected, the list for that state is filtered, if zipcodes are selected, it includes that list of hospitals in the search results.

Answer 1

Due to deferred execution, you can piece your query together more dynamically:

var query = context.Hospitals;
if (HospitalIDsByState.Any())
  query = query.Where(h => HospitalIDsByState.Contains(h.state));
if (HospitalIDsByCity.Any())
  query = query.Where(h => HospitalIDsByCity.Contains(h.city));
if (HospitalIDsByZipcodes.Any())
  query = query.Where(h => HospitalIDsByZipcodes(h.zipcode));

return query;

The advantage here is that only the relevant query parts are pushed to your database and you don't end up checking things that you don't need to.