How to learn to represent complicated relationship in Django model? -


consider train ticket booking app. there many cities, stations , trains.

each city has one/more stations. obvious station can not in more 1 city. each station receive one/more train(s). every train visits 1 or more station , stops @ fixed (common) destination.

want make form user able select city, stations in same city , train (which station of city receives) , book train.
have done till now.

class city(models.model):     name = models.charfield(max_length=50, help_text="your city name")  class train(models.model):     number = models.integerfield(primary_key=true)     name = models.charfield(max_length=50, help_text="train")     city = models.foreignkey(city)    class station(models.model):    city = models.foreignkey(city)    name = models.charfield(max_length=50, help_text="all available stations in city")  class bookedticket(models.model):    city = models.foreignkey(city)    station = models.foreignkey(station)    train = models.foreignkey(train)

please suggest on how establish relationships because not able display correct stations chosen city , similarly, train chosen city , station.

you use _set find stations in city

my_city = city.objects.get(name="my hometown")  stations_in_city = my_city.station_set.all()

also see documentation here , here examples.


Comments

Post a Comment

Popular posts from this blog

inversion of control - Autofac named registration constructor injection -

does autofac support specifying registration name in components' constructors? example: ninject's namedattribute . you need use autofac.extras.attributed package on top achieve this so let's have 1 interface , 2 classes: public interface ihello { string sayhello(); } public class englishhello : ihello { public string sayhello() { return "hello"; } } public class frenchhello : ihello { public string sayhello() { return "bonjour"; } } then have consumer class, in want select instance injected: public class helloconsumer { private readonly ihello helloservice; public helloconsumer([withkey("en")] ihello helloservice) { if (helloservice == null) { throw new argumentnullexception("helloservice"); } this.helloservice = helloservice; } public string sayhello() { return this.helloservice.sayhello()...
Read more

verilog - Systemverilog dynamic casting issues -

i've code snippet following in testbench function void write_to_port( my_data_type_base data ); my_data_type_extended data_ext; if(!$cast(data_ext, data)); `uvm_error(get_type_name(), "failed cast"); `uvm_info(get_name(), $psprintf("data_ext :\n%s", data_ext.sprint()), uvm_medium) // write data_ext out port.... endfunction when run it, i'm getting uvm_error "failed cast." i'm not quire sure why $cast not returning 1. can see, i'm printing out extended class data item after casting uvm_info. can see it's being cast properly. if don't use $cast if condition, don't runtime error. isn't coding practice use if dynamic cast check if $cast returning 1 ? what might reason behind cast not returning 1 in above case? i think semicolon on line 'if' not belong? i think consumes if statement, , uvm_error executes regardless of how if evaluates: if(!$cast(data_ext, data)); <- no semico...
Read more

ios - Change Storyboard View using Seague -

i have following code checks connection server, , depending on want change views if no connection found. nsstring *connect = [nsstring stringwithcontentsofurl:[nsurl urlwithstring:@"http://myserver.com"] encoding:nsutf8stringencoding error:nil]; if (connect == null) { [self performseguewithidentifier:@"network_failure" sender:self]; } else { // other code here } my problem not change views. have added storyboard segue between 2 views identifier of network_failure . not have navigation controller or that, problem? thanks help! no not problem. first of all, in objectivec exists nil object oriented null . must use that. so: if(connect == nil) or better: if(!connect) so due fact nil not same of null , probably code does't enter in if scope . you have been able discover breakpoint. anyway: be sure set trigger segue (line) 2 view controller , , name network_failure (that not best name. should instead view1toview2 ) as, m...
Read more